StandardMaterial Light Transmission (#8015)

# Objective

<img width="1920" alt="Screenshot 2023-04-26 at 01 07 34"
src="https://user-images.githubusercontent.com/418473/234467578-0f34187b-5863-4ea1-88e9-7a6bb8ce8da3.png">

This PR adds both diffuse and specular light transmission capabilities
to the `StandardMaterial`, with support for screen space refractions.
This enables realistically representing a wide range of real-world
materials, such as:

  - Glass; (Including frosted glass)
  - Transparent and translucent plastics;
  - Various liquids and gels;
  - Gemstones;
  - Marble;
  - Wax;
  - Paper;
  - Leaves;
  - Porcelain.

Unlike existing support for transparency, light transmission does not
rely on fixed function alpha blending, and therefore works with both
`AlphaMode::Opaque` and `AlphaMode::Mask` materials.

## Solution

- Introduces a number of transmission related fields in the
`StandardMaterial`;
- For specular transmission:
- Adds logic to take a view main texture snapshot after the opaque
phase; (in order to perform screen space refractions)
- Introduces a new `Transmissive3d` phase to the renderer, to which all
meshes with `transmission > 0.0` materials are sent.
- Calculates a light exit point (of the approximate mesh volume) using
`ior` and `thickness` properties
- Samples the snapshot texture with an adaptive number of taps across a
`roughness`-controlled radius enabling “blurry” refractions
- For diffuse transmission:
- Approximates transmitted diffuse light by using a second, flipped +
displaced, diffuse-only Lambertian lobe for each light source.

## To Do

- [x] Figure out where `fresnel_mix()` is taking place, if at all, and
where `dielectric_specular` is being calculated, if at all, and update
them to use the `ior` value (Not a blocker, just a nice-to-have for more
correct BSDF)
- To the _best of my knowledge, this is now taking place, after
964340cdd. The fresnel mix is actually "split" into two parts in our
implementation, one `(1 - fresnel(...))` in the transmission, and
`fresnel()` in the light implementations. A surface with more
reflectance now will produce slightly dimmer transmission towards the
grazing angle, as more of the light gets reflected.
- [x] Add `transmission_texture`
- [x] Add `diffuse_transmission_texture`
- [x] Add `thickness_texture`
- [x] Add `attenuation_distance` and `attenuation_color`
- [x] Connect values to glTF loader
  - [x] `transmission` and `transmission_texture`
  - [x] `thickness` and `thickness_texture`
  - [x] `ior`
- [ ] `diffuse_transmission` and `diffuse_transmission_texture` (needs
upstream support in `gltf` crate, not a blocker)
- [x] Add support for multiple screen space refraction “steps”
- [x] Conditionally create no transmission snapshot texture at all if
`steps == 0`
- [x] Conditionally enable/disable screen space refraction transmission
snapshots
- [x] Read from depth pre-pass to prevent refracting pixels in front of
the light exit point
- [x] Use `interleaved_gradient_noise()` function for sampling blur in a
way that benefits from TAA
- [x] Drill down a TAA `#define`, tweak some aspects of the effect
conditionally based on it
- [x] Remove const array that's crashing under HLSL (unless a new `naga`
release with https://github.com/gfx-rs/naga/pull/2496 comes out before
we merge this)
- [ ] Look into alternatives to the `switch` hack for dynamically
indexing the const array (might not be needed, compilers seem to be
decent at expanding it)
- [ ] Add pipeline keys for gating transmission (do we really want/need
this?)
- [x] Tweak some material field/function names?

## A Note on Texture Packing

_This was originally added as a comment to the
`specular_transmission_texture`, `thickness_texture` and
`diffuse_transmission_texture` documentation, I removed it since it was
more confusing than helpful, and will likely be made redundant/will need
to be updated once we have a better infrastructure for preprocessing
assets_

Due to how channels are mapped, you can more efficiently use a single
shared texture image
for configuring the following:

- R - `specular_transmission_texture`
- G - `thickness_texture`
- B - _unused_
- A - `diffuse_transmission_texture`

The `KHR_materials_diffuse_transmission` glTF extension also defines a
`diffuseTransmissionColorTexture`,
that _we don't currently support_. One might choose to pack the
intensity and color textures together,
using RGB for the color and A for the intensity, in which case this
packing advice doesn't really apply.

---

## Changelog

- Added a new `Transmissive3d` render phase for rendering specular
transmissive materials with screen space refractions
- Added rendering support for transmitted environment map light on the
`StandardMaterial` as a fallback for screen space refractions
- Added `diffuse_transmission`, `specular_transmission`, `thickness`,
`ior`, `attenuation_distance` and `attenuation_color` to the
`StandardMaterial`
- Added `diffuse_transmission_texture`, `specular_transmission_texture`,
`thickness_texture` to the `StandardMaterial`, gated behind a new
`pbr_transmission_textures` cargo feature (off by default, for maximum
hardware compatibility)
- Added `Camera3d::screen_space_specular_transmission_steps` for
controlling the number of “layers of transparency” rendered for
transmissive objects
- Added a `TransmittedShadowReceiver` component for enabling shadows in
(diffusely) transmitted light. (disabled by default, as it requires
carefully setting up the `thickness` to avoid self-shadow artifacts)
- Added support for the `KHR_materials_transmission`,
`KHR_materials_ior` and `KHR_materials_volume` glTF extensions
- Renamed items related to temporal jitter for greater consistency

## Migration Guide

- `SsaoPipelineKey::temporal_noise` has been renamed to
`SsaoPipelineKey::temporal_jitter`
- The `TAA` shader def (controlled by the presence of the
`TemporalAntiAliasSettings` component in the camera) has been replaced
with the `TEMPORAL_JITTER` shader def (controlled by the presence of the
`TemporalJitter` component in the camera)
- `MeshPipelineKey::TAA` has been replaced by
`MeshPipelineKey::TEMPORAL_JITTER`
- The `TEMPORAL_NOISE` shader def has been consolidated with
`TEMPORAL_JITTER`

Cargo.toml

@@ -260,6 +260,9 @@ shader_format_glsl = ["bevy_internal/shader_format_glsl"]
 # Enable support for shaders in SPIR-V
 shader_format_spirv = ["bevy_internal/shader_format_spirv"]
 
+# Enable support for transmission-related textures in the `StandardMaterial`, at the risk of blowing past the global, per-shader texture limit on older/lower-end GPUs
+pbr_transmission_textures = ["bevy_internal/pbr_transmission_textures"]
+
 # Enable some limitations to be able to use WebGL2. If not enabled, it will default to WebGPU in Wasm. Please refer to the [WebGL2 and WebGPU](https://github.com/bevyengine/bevy/tree/latest/examples#webgl2-and-webgpu) section of the examples README for more information on how to run Wasm builds with WebGPU.
 webgl2 = ["bevy_internal/webgl"]
 
@@ -800,6 +803,16 @@ description = "Demonstrates transparency in 3d"
 category = "3D Rendering"
 wasm = true
 
+[[example]]
+name = "transmission"
+path = "examples/3d/transmission.rs"
+
+[package.metadata.example.transmission]
+name = "Transmission"
+description = "Showcases light transmission in the PBR material"
+category = "3D Rendering"
+wasm = true
+
 [[example]]
 name = "two_passes"
 path = "examples/3d/two_passes.rs"

crates/bevy_core_pipeline/src/core_3d/camera_3d.rs

@@ -25,6 +25,31 @@ pub struct Camera3d {
     pub depth_load_op: Camera3dDepthLoadOp,
     /// The texture usages for the depth texture created for the main 3d pass.
     pub depth_texture_usages: Camera3dDepthTextureUsage,
+    /// How many individual steps should be performed in the [`Transmissive3d`](crate::core_3d::Transmissive3d) pass.
+    ///
+    /// Roughly corresponds to how many “layers of transparency” are rendered for screen space
+    /// specular transmissive objects. Each step requires making one additional
+    /// texture copy, so it's recommended to keep this number to a resonably low value. Defaults to `1`.
+    ///
+    /// ### Notes
+    ///
+    /// - No copies will be performed if there are no transmissive materials currently being rendered,
+    ///   regardless of this setting.
+    /// - Setting this to `0` disables the screen-space refraction effect entirely, and falls
+    ///   back to refracting only the environment map light's texture.
+    /// - If set to more than `0`, any opaque [`clear_color`](Camera3d::clear_color) will obscure the environment
+    ///   map light's texture, preventing it from being visible “through” transmissive materials. If you'd like
+    ///   to still have the environment map show up in your refractions, you can set the clear color's alpha to `0.0`.
+    ///   Keep in mind that depending on the platform and your window settings, this may cause the window to become
+    ///   transparent.
+    pub screen_space_specular_transmission_steps: usize,
+    /// The quality of the screen space specular transmission blur effect, applied to whatever's “behind” transmissive
+    /// objects when their `roughness` is greater than `0.0`.
+    ///
+    /// Higher qualities are more GPU-intensive.
+    ///
+    /// **Note:** You can get better-looking results at any quality level by enabling TAA. See: [`TemporalAntiAliasPlugin`](crate::experimental::taa::TemporalAntiAliasPlugin).
+    pub screen_space_specular_transmission_quality: ScreenSpaceTransmissionQuality,
 }
 
 impl Default for Camera3d {
@@ -33,6 +58,8 @@ impl Default for Camera3d {
             clear_color: ClearColorConfig::Default,
             depth_load_op: Default::default(),
             depth_texture_usages: TextureUsages::RENDER_ATTACHMENT.into(),
+            screen_space_specular_transmission_steps: 1,
+            screen_space_specular_transmission_quality: Default::default(),
         }
     }
 }
@@ -77,6 +104,37 @@ impl From<Camera3dDepthLoadOp> for LoadOp<f32> {
     }
 }
 
+/// The quality of the screen space transmission blur effect, applied to whatever's “behind” transmissive
+/// objects when their `roughness` is greater than `0.0`.
+///
+/// Higher qualities are more GPU-intensive.
+///
+/// **Note:** You can get better-looking results at any quality level by enabling TAA. See: [`TemporalAntiAliasPlugin`](crate::experimental::taa::TemporalAntiAliasPlugin).
+#[derive(Resource, Default, Clone, Copy, Reflect, PartialEq, PartialOrd, Debug)]
+#[reflect(Resource)]
+pub enum ScreenSpaceTransmissionQuality {
+    /// Best performance at the cost of quality. Suitable for lower end GPUs. (e.g. Mobile)
+    ///
+    /// `num_taps` = 4
+    Low,
+
+    /// A balanced option between quality and performance.
+    ///
+    /// `num_taps` = 8
+    #[default]
+    Medium,
+
+    /// Better quality. Suitable for high end GPUs. (e.g. Desktop)
+    ///
+    /// `num_taps` = 16
+    High,
+
+    /// The highest quality, suitable for non-realtime rendering. (e.g. Pre-rendered cinematics and photo mode)
+    ///
+    /// `num_taps` = 32
+    Ultra,
+}
+
 #[derive(Bundle)]
 pub struct Camera3dBundle {
     pub camera: Camera,

crates/bevy_core_pipeline/src/core_3d/main_transmissive_pass_3d_node.rs

@@ -0,0 +1,148 @@
+use super::{Camera3d, ViewTransmissionTexture};
+use crate::core_3d::Transmissive3d;
+use bevy_ecs::{prelude::*, query::QueryItem};
+use bevy_render::{
+    camera::ExtractedCamera,
+    render_graph::{NodeRunError, RenderGraphContext, ViewNode},
+    render_phase::RenderPhase,
+    render_resource::{
+        Extent3d, LoadOp, Operations, RenderPassDepthStencilAttachment, RenderPassDescriptor,
+    },
+    renderer::RenderContext,
+    view::{ViewDepthTexture, ViewTarget},
+};
+#[cfg(feature = "trace")]
+use bevy_utils::tracing::info_span;
+use std::ops::Range;
+
+/// A [`bevy_render::render_graph::Node`] that runs the [`Transmissive3d`] [`RenderPhase`].
+#[derive(Default)]
+pub struct MainTransmissivePass3dNode;
+
+impl ViewNode for MainTransmissivePass3dNode {
+    type ViewQuery = (
+        &'static ExtractedCamera,
+        &'static Camera3d,
+        &'static RenderPhase<Transmissive3d>,
+        &'static ViewTarget,
+        Option<&'static ViewTransmissionTexture>,
+        &'static ViewDepthTexture,
+    );
+
+    fn run(
+        &self,
+        graph: &mut RenderGraphContext,
+        render_context: &mut RenderContext,
+        (camera, camera_3d, transmissive_phase, target, transmission, depth): QueryItem<
+            Self::ViewQuery,
+        >,
+        world: &World,
+    ) -> Result<(), NodeRunError> {
+        let view_entity = graph.view_entity();
+
+        let physical_target_size = camera.physical_target_size.unwrap();
+
+        let render_pass_descriptor = RenderPassDescriptor {
+            label: Some("main_transmissive_pass_3d"),
+            // NOTE: The transmissive pass loads the color buffer as well as overwriting it where appropriate.
+            color_attachments: &[Some(target.get_color_attachment(Operations {
+                load: LoadOp::Load,
+                store: true,
+            }))],
+            depth_stencil_attachment: Some(RenderPassDepthStencilAttachment {
+                view: &depth.view,
+                // NOTE: The transmissive main pass loads the depth buffer and possibly overwrites it
+                depth_ops: Some(Operations {
+                    load: LoadOp::Load,
+                    store: true,
+                }),
+                stencil_ops: None,
+            }),
+        };
+
+        // Run the transmissive pass, sorted back-to-front
+        // NOTE: Scoped to drop the mutable borrow of render_context
+        #[cfg(feature = "trace")]
+        let _main_transmissive_pass_3d_span = info_span!("main_transmissive_pass_3d").entered();
+
+        if !transmissive_phase.items.is_empty() {
+            let screen_space_specular_transmission_steps =
+                camera_3d.screen_space_specular_transmission_steps;
+            if screen_space_specular_transmission_steps > 0 {
+                let transmission =
+                    transmission.expect("`ViewTransmissionTexture` should exist at this point");
+
+                // `transmissive_phase.items` are depth sorted, so we split them into N = `screen_space_specular_transmission_steps`
+                // ranges, rendering them back-to-front in multiple steps, allowing multiple levels of transparency.
+                //
+                // Note: For the sake of simplicity, we currently split items evenly among steps. In the future, we
+                // might want to use a more sophisticated heuristic (e.g. based on view bounds, or with an exponential
+                // falloff so that nearby objects have more levels of transparency available to them)
+                for range in split_range(
+                    0..transmissive_phase.items.len(),
+                    screen_space_specular_transmission_steps,
+                ) {
+                    // Copy the main texture to the transmission texture, allowing to use the color output of the
+                    // previous step (or of the `Opaque3d` phase, for the first step) as a transmissive color input
+                    render_context.command_encoder().copy_texture_to_texture(
+                        target.main_texture().as_image_copy(),
+                        transmission.texture.as_image_copy(),
+                        Extent3d {
+                            width: physical_target_size.x,
+                            height: physical_target_size.y,
+                            depth_or_array_layers: 1,
+                        },
+                    );
+
+                    let mut render_pass =
+                        render_context.begin_tracked_render_pass(render_pass_descriptor.clone());
+
+                    if let Some(viewport) = camera.viewport.as_ref() {
+                        render_pass.set_camera_viewport(viewport);
+                    }
+
+                    // render items in range
+                    transmissive_phase.render_range(&mut render_pass, world, view_entity, range);
+                }
+            } else {
+                let mut render_pass =
+                    render_context.begin_tracked_render_pass(render_pass_descriptor);
+
+                if let Some(viewport) = camera.viewport.as_ref() {
+                    render_pass.set_camera_viewport(viewport);
+                }
+
+                transmissive_phase.render(&mut render_pass, world, view_entity);
+            }
+        }
+
+        Ok(())
+    }
+}
+
+/// Splits a [`Range`] into at most `max_num_splits` sub-ranges without overlaps
+///
+/// Properly takes into account remainders of inexact divisions (by adding extra
+/// elements to the initial sub-ranges as needed)
+fn split_range(range: Range<usize>, max_num_splits: usize) -> impl Iterator<Item = Range<usize>> {
+    let len = range.end - range.start;
+    assert!(len > 0, "to be split, a range must not be empty");
+    assert!(max_num_splits > 0, "max_num_splits must be at least 1");
+    let num_splits = max_num_splits.min(len);
+    let step = len / num_splits;
+    let mut rem = len % num_splits;
+    let mut start = range.start;
+
+    (0..num_splits).map(move |_| {
+        let extra = if rem > 0 {
+            rem -= 1;
+            1
+        } else {
+            0
+        };
+        let end = (start + step + extra).min(range.end);
+        let result = start..end;
+        start = end;
+        result
+    })
+}

crates/bevy_core_pipeline/src/core_3d/mod.rs

@@ -1,5 +1,6 @@
 mod camera_3d;
 mod main_opaque_pass_3d_node;
+mod main_transmissive_pass_3d_node;
 mod main_transparent_pass_3d_node;
 
 pub mod graph {
@@ -15,6 +16,7 @@ pub mod graph {
         pub const END_PREPASSES: &str = "end_prepasses";
         pub const START_MAIN_PASS: &str = "start_main_pass";
         pub const MAIN_OPAQUE_PASS: &str = "main_opaque_pass";
+        pub const MAIN_TRANSMISSIVE_PASS: &str = "main_transmissive_pass";
         pub const MAIN_TRANSPARENT_PASS: &str = "main_transparent_pass";
         pub const END_MAIN_PASS: &str = "end_main_pass";
         pub const BLOOM: &str = "bloom";
@@ -48,17 +50,18 @@ use bevy_render::{
         RenderPhase,
     },
     render_resource::{
-        CachedRenderPipelineId, Extent3d, TextureDescriptor, TextureDimension, TextureFormat,
-        TextureUsages,
+        CachedRenderPipelineId, Extent3d, FilterMode, Sampler, SamplerDescriptor, Texture,
+        TextureDescriptor, TextureDimension, TextureFormat, TextureUsages, TextureView,
     },
     renderer::RenderDevice,
-    texture::TextureCache,
-    view::ViewDepthTexture,
+    texture::{BevyDefault, TextureCache},
+    view::{ExtractedView, ViewDepthTexture, ViewTarget},
     Extract, ExtractSchedule, Render, RenderApp, RenderSet,
 };
 use bevy_utils::{nonmax::NonMaxU32, tracing::warn, FloatOrd, HashMap};
 
 use crate::{
+    core_3d::main_transmissive_pass_3d_node::MainTransmissivePass3dNode,
     deferred::{
         copy_lighting_id::CopyDeferredLightingIdNode, node::DeferredGBufferPrepassNode,
         AlphaMask3dDeferred, Opaque3dDeferred, DEFERRED_LIGHTING_PASS_ID_FORMAT,
@@ -91,6 +94,7 @@ impl Plugin for Core3dPlugin {
         render_app
             .init_resource::<DrawFunctions<Opaque3d>>()
             .init_resource::<DrawFunctions<AlphaMask3d>>()
+            .init_resource::<DrawFunctions<Transmissive3d>>()
             .init_resource::<DrawFunctions<Transparent3d>>()
             .init_resource::<DrawFunctions<Opaque3dPrepass>>()
             .init_resource::<DrawFunctions<AlphaMask3dPrepass>>()
@@ -103,12 +107,14 @@ impl Plugin for Core3dPlugin {
                 (
                     sort_phase_system::<Opaque3d>.in_set(RenderSet::PhaseSort),
                     sort_phase_system::<AlphaMask3d>.in_set(RenderSet::PhaseSort),
+                    sort_phase_system::<Transmissive3d>.in_set(RenderSet::PhaseSort),
                     sort_phase_system::<Transparent3d>.in_set(RenderSet::PhaseSort),
                     sort_phase_system::<Opaque3dPrepass>.in_set(RenderSet::PhaseSort),
                     sort_phase_system::<AlphaMask3dPrepass>.in_set(RenderSet::PhaseSort),
                     sort_phase_system::<Opaque3dDeferred>.in_set(RenderSet::PhaseSort),
                     sort_phase_system::<AlphaMask3dDeferred>.in_set(RenderSet::PhaseSort),
                     prepare_core_3d_depth_textures.in_set(RenderSet::PrepareResources),
+                    prepare_core_3d_transmission_textures.in_set(RenderSet::PrepareResources),
                     prepare_prepass_textures.in_set(RenderSet::PrepareResources),
                 ),
             );
@@ -131,6 +137,10 @@ impl Plugin for Core3dPlugin {
                 CORE_3D,
                 MAIN_OPAQUE_PASS,
             )
+            .add_render_graph_node::<ViewNodeRunner<MainTransmissivePass3dNode>>(
+                CORE_3D,
+                MAIN_TRANSMISSIVE_PASS,
+            )
             .add_render_graph_node::<ViewNodeRunner<MainTransparentPass3dNode>>(
                 CORE_3D,
                 MAIN_TRANSPARENT_PASS,
@@ -148,6 +158,7 @@ impl Plugin for Core3dPlugin {
                     END_PREPASSES,
                     START_MAIN_PASS,
                     MAIN_OPAQUE_PASS,
+                    MAIN_TRANSMISSIVE_PASS,
                     MAIN_TRANSPARENT_PASS,
                     END_MAIN_PASS,
                     TONEMAPPING,
@@ -282,6 +293,78 @@ impl CachedRenderPipelinePhaseItem for AlphaMask3d {
     }
 }
 
+pub struct Transmissive3d {
+    pub distance: f32,
+    pub pipeline: CachedRenderPipelineId,
+    pub entity: Entity,
+    pub draw_function: DrawFunctionId,
+    pub batch_range: Range<u32>,
+    pub dynamic_offset: Option<NonMaxU32>,
+}
+
+impl PhaseItem for Transmissive3d {
+    // NOTE: Values increase towards the camera. Back-to-front ordering for transmissive means we need an ascending sort.
+    type SortKey = FloatOrd;
+
+    /// For now, automatic batching is disabled for transmissive items because their rendering is
+    /// split into multiple steps depending on [`Camera3d::screen_space_specular_transmission_steps`],
+    /// which the batching system doesn't currently know about.
+    ///
+    /// Having batching enabled would cause the same item to be drawn multiple times across different
+    /// steps, whenever the batching range crossed a step boundary.
+    ///
+    /// Eventually, we could add support for this by having the batching system break up the batch ranges
+    /// using the same logic as the transmissive pass, but for now it's simpler to just disable batching.
+    const AUTOMATIC_BATCHING: bool = false;
+
+    #[inline]
+    fn entity(&self) -> Entity {
+        self.entity
+    }
+
+    #[inline]
+    fn sort_key(&self) -> Self::SortKey {
+        FloatOrd(self.distance)
+    }
+
+    #[inline]
+    fn draw_function(&self) -> DrawFunctionId {
+        self.draw_function
+    }
+
+    #[inline]
+    fn sort(items: &mut [Self]) {
+        radsort::sort_by_key(items, |item| item.distance);
+    }
+
+    #[inline]
+    fn batch_range(&self) -> &Range<u32> {
+        &self.batch_range
+    }
+
+    #[inline]
+    fn batch_range_mut(&mut self) -> &mut Range<u32> {
+        &mut self.batch_range
+    }
+
+    #[inline]
+    fn dynamic_offset(&self) -> Option<NonMaxU32> {
+        self.dynamic_offset
+    }
+
+    #[inline]
+    fn dynamic_offset_mut(&mut self) -> &mut Option<NonMaxU32> {
+        &mut self.dynamic_offset
+    }
+}
+
+impl CachedRenderPipelinePhaseItem for Transmissive3d {
+    #[inline]
+    fn cached_pipeline(&self) -> CachedRenderPipelineId {
+        self.pipeline
+    }
+}
+
 pub struct Transparent3d {
     pub distance: f32,
     pub pipeline: CachedRenderPipelineId,
@@ -352,6 +435,7 @@ pub fn extract_core_3d_camera_phases(
             commands.get_or_spawn(entity).insert((
                 RenderPhase::<Opaque3d>::default(),
                 RenderPhase::<AlphaMask3d>::default(),
+                RenderPhase::<Transmissive3d>::default(),
                 RenderPhase::<Transparent3d>::default(),
             ));
         }
@@ -424,6 +508,7 @@ pub fn prepare_core_3d_depth_textures(
         (
             With<RenderPhase<Opaque3d>>,
             With<RenderPhase<AlphaMask3d>>,
+            With<RenderPhase<Transmissive3d>>,
             With<RenderPhase<Transparent3d>>,
         ),
     >,
@@ -484,6 +569,96 @@ pub fn prepare_core_3d_depth_textures(
     }
 }
 
+#[derive(Component)]
+pub struct ViewTransmissionTexture {
+    pub texture: Texture,
+    pub view: TextureView,
+    pub sampler: Sampler,
+}
+
+pub fn prepare_core_3d_transmission_textures(
+    mut commands: Commands,
+    mut texture_cache: ResMut<TextureCache>,
+    render_device: Res<RenderDevice>,
+    views_3d: Query<
+        (
+            Entity,
+            &ExtractedCamera,
+            &Camera3d,
+            &ExtractedView,
+            &RenderPhase<Transmissive3d>,
+        ),
+        (
+            With<RenderPhase<Opaque3d>>,
+            With<RenderPhase<AlphaMask3d>>,
+            With<RenderPhase<Transparent3d>>,
+        ),
+    >,
+) {
+    let mut textures = HashMap::default();
+    for (entity, camera, camera_3d, view, transmissive_3d_phase) in &views_3d {
+        let Some(physical_target_size) = camera.physical_target_size else {
+            continue;
+        };
+
+        // Don't prepare a transmission texture if the number of steps is set to 0
+        if camera_3d.screen_space_specular_transmission_steps == 0 {
+            continue;
+        }
+
+        // Don't prepare a transmission texture if there are no transmissive items to render
+        if transmissive_3d_phase.items.is_empty() {
+            continue;
+        }
+
+        let cached_texture = textures
+            .entry(camera.target.clone())
+            .or_insert_with(|| {
+                let usage = TextureUsages::TEXTURE_BINDING | TextureUsages::COPY_DST;
+
+                // The size of the transmission texture
+                let size = Extent3d {
+                    depth_or_array_layers: 1,
+                    width: physical_target_size.x,
+                    height: physical_target_size.y,
+                };
+
+                let format = if view.hdr {
+                    ViewTarget::TEXTURE_FORMAT_HDR
+                } else {
+                    TextureFormat::bevy_default()
+                };
+
+                let descriptor = TextureDescriptor {
+                    label: Some("view_transmission_texture"),
+                    size,
+                    mip_level_count: 1,
+                    sample_count: 1, // No need for MSAA, as we'll only copy the main texture here
+                    dimension: TextureDimension::D2,
+                    format,
+                    usage,
+                    view_formats: &[],
+                };
+
+                texture_cache.get(&render_device, descriptor)
+            })
+            .clone();
+
+        let sampler = render_device.create_sampler(&SamplerDescriptor {
+            label: Some("view_transmission_sampler"),
+            mag_filter: FilterMode::Linear,
+            min_filter: FilterMode::Linear,
+            ..Default::default()
+        });
+
+        commands.entity(entity).insert(ViewTransmissionTexture {
+            texture: cached_texture.texture,
+            view: cached_texture.default_view,
+            sampler,
+        });
+    }
+}
+
 // Disable MSAA and warn if using deferred rendering
 pub fn check_msaa(
     mut msaa: ResMut<Msaa>,

crates/bevy_core_pipeline/src/tonemapping/tonemapping_shared.wgsl

@@ -316,3 +316,12 @@ fn tone_mapping(in: vec4<f32>, color_grading: ColorGrading) -> vec4<f32> {
     return vec4(color, in.a);
 }
 
+// This is an **incredibly crude** approximation of the inverse of the tone mapping function.
+// We assume here that there's a simple linear relationship between the input and output
+// which is not true at all, but useful to at least preserve the overall luminance of colors
+// when sampling from an already tonemapped image. (e.g. for transmissive materials when HDR is off)
+fn approximate_inverse_tone_mapping(in: vec4<f32>, color_grading: ColorGrading) -> vec4<f32> {
+    let out = tone_mapping(in, color_grading);
+    let approximate_ratio = length(in.rgb) / length(out.rgb);
+    return vec4(in.rgb * approximate_ratio, in.a);
+}

crates/bevy_gltf/Cargo.toml

@@ -8,6 +8,9 @@ repository = "https://github.com/bevyengine/bevy"
 license = "MIT OR Apache-2.0"
 keywords = ["bevy"]
 
+[features]
+pbr_transmission_textures = []
+
 [dependencies]
 # bevy
 bevy_animation = { path = "../bevy_animation", version = "0.12.0-dev", optional = true }
@@ -30,6 +33,9 @@ bevy_utils = { path = "../bevy_utils", version = "0.12.0-dev" }
 # other
 gltf = { version = "1.3.0", default-features = false, features = [
     "KHR_lights_punctual",
+    "KHR_materials_transmission",
+    "KHR_materials_ior",
+    "KHR_materials_volume",
     "KHR_materials_unlit",
     "KHR_materials_emissive_strength",
     "extras",

crates/bevy_gltf/src/loader.rs

@@ -763,6 +763,56 @@ fn load_material(
             texture_handle(load_context, &info.texture())
         });
 
+        #[cfg(feature = "pbr_transmission_textures")]
+        let (specular_transmission, specular_transmission_texture) =
+            material.transmission().map_or((0.0, None), |transmission| {
+                let transmission_texture: Option<Handle<Image>> = transmission
+                    .transmission_texture()
+                    .map(|transmission_texture| {
+                        // TODO: handle transmission_texture.tex_coord() (the *set* index for the right texcoords)
+                        texture_handle(load_context, &transmission_texture.texture())
+                    });
+
+                (transmission.transmission_factor(), transmission_texture)
+            });
+
+        #[cfg(not(feature = "pbr_transmission_textures"))]
+        let specular_transmission = material
+            .transmission()
+            .map_or(0.0, |transmission| transmission.transmission_factor());
+
+        #[cfg(feature = "pbr_transmission_textures")]
+        let (thickness, thickness_texture, attenuation_distance, attenuation_color) = material
+            .volume()
+            .map_or((0.0, None, f32::INFINITY, [1.0, 1.0, 1.0]), |volume| {
+                let thickness_texture: Option<Handle<Image>> =
+                    volume.thickness_texture().map(|thickness_texture| {
+                        // TODO: handle thickness_texture.tex_coord() (the *set* index for the right texcoords)
+                        texture_handle(load_context, &thickness_texture.texture())
+                    });
+
+                (
+                    volume.thickness_factor(),
+                    thickness_texture,
+                    volume.attenuation_distance(),
+                    volume.attenuation_color(),
+                )
+            });
+
+        #[cfg(not(feature = "pbr_transmission_textures"))]
+        let (thickness, attenuation_distance, attenuation_color) =
+            material
+                .volume()
+                .map_or((0.0, f32::INFINITY, [1.0, 1.0, 1.0]), |volume| {
+                    (
+                        volume.thickness_factor(),
+                        volume.attenuation_distance(),
+                        volume.attenuation_color(),
+                    )
+                });
+
+        let ior = material.ior().unwrap_or(1.5);
+
         StandardMaterial {
             base_color: Color::rgba_linear(color[0], color[1], color[2], color[3]),
             base_color_texture,
@@ -782,6 +832,19 @@ fn load_material(
             emissive: Color::rgb_linear(emissive[0], emissive[1], emissive[2])
                 * material.emissive_strength().unwrap_or(1.0),
             emissive_texture,
+            specular_transmission,
+            #[cfg(feature = "pbr_transmission_textures")]
+            specular_transmission_texture,
+            thickness,
+            #[cfg(feature = "pbr_transmission_textures")]
+            thickness_texture,
+            ior,
+            attenuation_distance,
+            attenuation_color: Color::rgb_linear(
+                attenuation_color[0],
+                attenuation_color[1],
+                attenuation_color[2],
+            ),
             unlit: material.unlit(),
             alpha_mode: alpha_mode(material),
             ..Default::default()

crates/bevy_internal/Cargo.toml

@@ -72,6 +72,9 @@ x11 = ["bevy_winit/x11"]
 # enable rendering of font glyphs using subpixel accuracy
 subpixel_glyph_atlas = ["bevy_text/subpixel_glyph_atlas"]
 
+# Transmission textures in `StandardMaterial`:
+pbr_transmission_textures = ["bevy_pbr?/pbr_transmission_textures", "bevy_gltf?/pbr_transmission_textures"]
+
 # Optimise for WebGL2
 webgl = ["bevy_core_pipeline?/webgl", "bevy_pbr?/webgl", "bevy_render?/webgl", "bevy_gizmos?/webgl", "bevy_sprite?/webgl"]
 

crates/bevy_pbr/Cargo.toml

@@ -10,6 +10,7 @@ keywords = ["bevy"]
 
 [features]
 webgl = []
+pbr_transmission_textures = []
 
 [dependencies]
 # bevy

crates/bevy_pbr/src/extended_material.rs

@@ -199,6 +199,10 @@ impl<B: Material, E: MaterialExtension> Material for ExtendedMaterial<B, E> {
         B::depth_bias(&self.base)
     }
 
+    fn reads_view_transmission_texture(&self) -> bool {
+        B::reads_view_transmission_texture(&self.base)
+    }
+
     fn opaque_render_method(&self) -> crate::OpaqueRendererMethod {
         B::opaque_render_method(&self.base)
     }

crates/bevy_pbr/src/lib.rs

@@ -73,6 +73,7 @@ pub const PBR_BINDINGS_SHADER_HANDLE: Handle<Shader> = Handle::weak_from_u128(56
 pub const UTILS_HANDLE: Handle<Shader> = Handle::weak_from_u128(1900548483293416725);
 pub const CLUSTERED_FORWARD_HANDLE: Handle<Shader> = Handle::weak_from_u128(166852093121196815);
 pub const PBR_LIGHTING_HANDLE: Handle<Shader> = Handle::weak_from_u128(14170772752254856967);
+pub const PBR_TRANSMISSION_HANDLE: Handle<Shader> = Handle::weak_from_u128(77319684653223658032);
 pub const SHADOWS_HANDLE: Handle<Shader> = Handle::weak_from_u128(11350275143789590502);
 pub const SHADOW_SAMPLING_HANDLE: Handle<Shader> = Handle::weak_from_u128(3145627513789590502);
 pub const PBR_FRAGMENT_HANDLE: Handle<Shader> = Handle::weak_from_u128(2295049283805286543);
@@ -135,6 +136,12 @@ impl Plugin for PbrPlugin {
             "render/pbr_lighting.wgsl",
             Shader::from_wgsl
         );
+        load_internal_asset!(
+            app,
+            PBR_TRANSMISSION_HANDLE,
+            "render/pbr_transmission.wgsl",
+            Shader::from_wgsl
+        );
         load_internal_asset!(
             app,
             SHADOWS_HANDLE,

crates/bevy_pbr/src/light.rs

@@ -598,9 +598,23 @@ impl Default for AmbientLight {
 #[reflect(Component, Default)]
 pub struct NotShadowCaster;
 /// Add this component to make a [`Mesh`](bevy_render::mesh::Mesh) not receive shadows.
+///
+/// **Note:** If you're using diffuse transmission, setting [`NotShadowReceiver`] will
+/// cause both “regular” shadows as well as diffusely transmitted shadows to be disabled,
+/// even when [`TransmittedShadowReceiver`] is being used.
 #[derive(Component, Reflect, Default)]
 #[reflect(Component, Default)]
 pub struct NotShadowReceiver;
+/// Add this component to make a [`Mesh`](bevy_render::mesh::Mesh) using a PBR material with [`diffuse_transmission`](crate::pbr_material::StandardMaterial::diffuse_transmission)`> 0.0`
+/// receive shadows on its diffuse transmission lobe. (i.e. its “backside”)
+///
+/// Not enabled by default, as it requires carefully setting up [`thickness`](crate::pbr_material::StandardMaterial::thickness)
+/// (and potentially even baking a thickness texture!) to match the geometry of the mesh, in order to avoid self-shadow artifacts.
+///
+/// **Note:** Using [`NotShadowReceiver`] overrides this component.
+#[derive(Component, Reflect, Default)]
+#[reflect(Component, Default)]
+pub struct TransmittedShadowReceiver;
 
 /// Add this component to a [`Camera3d`](bevy_core_pipeline::core_3d::Camera3d)
 /// to control how to anti-alias shadow edges.

crates/bevy_pbr/src/material.rs

@@ -2,8 +2,10 @@ use crate::*;
 use bevy_app::{App, Plugin};
 use bevy_asset::{Asset, AssetApp, AssetEvent, AssetId, AssetServer, Assets, Handle};
 use bevy_core_pipeline::{
-    core_3d::{AlphaMask3d, Opaque3d, Transparent3d},
-    experimental::taa::TemporalAntiAliasSettings,
+    core_3d::{
+        AlphaMask3d, Camera3d, Opaque3d, ScreenSpaceTransmissionQuality, Transmissive3d,
+        Transparent3d,
+    },
     prepass::{DeferredPrepass, DepthPrepass, MotionVectorPrepass, NormalPrepass},
     tonemapping::{DebandDither, Tonemapping},
 };
@@ -15,6 +17,7 @@ use bevy_ecs::{
 use bevy_reflect::Reflect;
 use bevy_render::{
     camera::Projection,
+    camera::TemporalJitter,
     extract_instances::{ExtractInstancesPlugin, ExtractedInstances},
     extract_resource::ExtractResource,
     mesh::{Mesh, MeshVertexBufferLayout},
@@ -124,6 +127,15 @@ pub trait Material: Asset + AsBindGroup + Clone + Sized {
         0.0
     }
 
+    #[inline]
+    /// Returns whether the material would like to read from [`ViewTransmissionTexture`](bevy_core_pipeline::core_3d::ViewTransmissionTexture).
+    ///
+    /// This allows taking color output from the [`Opaque3d`] pass as an input, (for screen-space transmission) but requires
+    /// rendering to take place in a separate [`Transmissive3d`] pass.
+    fn reads_view_transmission_texture(&self) -> bool {
+        false
+    }
+
     /// Returns this material's prepass vertex shader. If [`ShaderRef::Default`] is returned, the default prepass vertex shader
     /// will be used.
     ///
@@ -203,6 +215,7 @@ where
             render_app
                 .init_resource::<DrawFunctions<Shadow>>()
                 .add_render_command::<Shadow, DrawPrepass<M>>()
+                .add_render_command::<Transmissive3d, DrawMaterial<M>>()
                 .add_render_command::<Transparent3d, DrawMaterial<M>>()
                 .add_render_command::<Opaque3d, DrawMaterial<M>>()
                 .add_render_command::<AlphaMask3d, DrawMaterial<M>>()
@@ -418,10 +431,30 @@ const fn tonemapping_pipeline_key(tonemapping: Tonemapping) -> MeshPipelineKey {
     }
 }
 
+const fn screen_space_specular_transmission_pipeline_key(
+    screen_space_transmissive_blur_quality: ScreenSpaceTransmissionQuality,
+) -> MeshPipelineKey {
+    match screen_space_transmissive_blur_quality {
+        ScreenSpaceTransmissionQuality::Low => {
+            MeshPipelineKey::SCREEN_SPACE_SPECULAR_TRANSMISSION_LOW
+        }
+        ScreenSpaceTransmissionQuality::Medium => {
+            MeshPipelineKey::SCREEN_SPACE_SPECULAR_TRANSMISSION_MEDIUM
+        }
+        ScreenSpaceTransmissionQuality::High => {
+            MeshPipelineKey::SCREEN_SPACE_SPECULAR_TRANSMISSION_HIGH
+        }
+        ScreenSpaceTransmissionQuality::Ultra => {
+            MeshPipelineKey::SCREEN_SPACE_SPECULAR_TRANSMISSION_ULTRA
+        }
+    }
+}
+
 #[allow(clippy::too_many_arguments)]
 pub fn queue_material_meshes<M: Material>(
     opaque_draw_functions: Res<DrawFunctions<Opaque3d>>,
     alpha_mask_draw_functions: Res<DrawFunctions<AlphaMask3d>>,
+    transmissive_draw_functions: Res<DrawFunctions<Transmissive3d>>,
     transparent_draw_functions: Res<DrawFunctions<Transparent3d>>,
     material_pipeline: Res<MaterialPipeline<M>>,
     mut pipelines: ResMut<SpecializedMeshPipelines<MaterialPipeline<M>>>,
@@ -446,10 +479,12 @@ pub fn queue_material_meshes<M: Material>(
             Has<MotionVectorPrepass>,
             Has<DeferredPrepass>,
         ),
-        Option<&TemporalAntiAliasSettings>,
+        Option<&Camera3d>,
+        Option<&TemporalJitter>,
         Option<&Projection>,
         &mut RenderPhase<Opaque3d>,
         &mut RenderPhase<AlphaMask3d>,
+        &mut RenderPhase<Transmissive3d>,
         &mut RenderPhase<Transparent3d>,
     )>,
 ) where
@@ -464,15 +499,18 @@ pub fn queue_material_meshes<M: Material>(
         shadow_filter_method,
         ssao,
         (normal_prepass, depth_prepass, motion_vector_prepass, deferred_prepass),
-        taa_settings,
+        camera_3d,
+        temporal_jitter,
         projection,
         mut opaque_phase,
         mut alpha_mask_phase,
+        mut transmissive_phase,
         mut transparent_phase,
     ) in &mut views
     {
         let draw_opaque_pbr = opaque_draw_functions.read().id::<DrawMaterial<M>>();
         let draw_alpha_mask_pbr = alpha_mask_draw_functions.read().id::<DrawMaterial<M>>();
+        let draw_transmissive_pbr = transmissive_draw_functions.read().id::<DrawMaterial<M>>();
         let draw_transparent_pbr = transparent_draw_functions.read().id::<DrawMaterial<M>>();
 
         let mut view_key = MeshPipelineKey::from_msaa_samples(msaa.samples())
@@ -494,9 +532,10 @@ pub fn queue_material_meshes<M: Material>(
             view_key |= MeshPipelineKey::DEFERRED_PREPASS;
         }
 
-        if taa_settings.is_some() {
-            view_key |= MeshPipelineKey::TAA;
+        if temporal_jitter.is_some() {
+            view_key |= MeshPipelineKey::TEMPORAL_JITTER;
         }
+
         let environment_map_loaded = environment_map.is_some_and(|map| map.is_loaded(&images));
 
         if environment_map_loaded {
@@ -534,6 +573,11 @@ pub fn queue_material_meshes<M: Material>(
         if ssao.is_some() {
             view_key |= MeshPipelineKey::SCREEN_SPACE_AMBIENT_OCCLUSION;
         }
+        if let Some(camera_3d) = camera_3d {
+            view_key |= screen_space_specular_transmission_pipeline_key(
+                camera_3d.screen_space_specular_transmission_quality,
+            );
+        }
         let rangefinder = view.rangefinder3d();
         for visible_entity in &visible_entities.entities {
             let Some(material_asset_id) = render_material_instances.get(visible_entity) else {
@@ -588,7 +632,16 @@ pub fn queue_material_meshes<M: Material>(
                 + material.properties.depth_bias;
             match material.properties.alpha_mode {
                 AlphaMode::Opaque => {
-                    if forward {
+                    if material.properties.reads_view_transmission_texture {
+                        transmissive_phase.add(Transmissive3d {
+                            entity: *visible_entity,
+                            draw_function: draw_transmissive_pbr,
+                            pipeline: pipeline_id,
+                            distance,
+                            batch_range: 0..1,
+                            dynamic_offset: None,
+                        });
+                    } else if forward {
                         opaque_phase.add(Opaque3d {
                             entity: *visible_entity,
                             draw_function: draw_opaque_pbr,
@@ -600,7 +653,16 @@ pub fn queue_material_meshes<M: Material>(
                     }
                 }
                 AlphaMode::Mask(_) => {
-                    if forward {
+                    if material.properties.reads_view_transmission_texture {
+                        transmissive_phase.add(Transmissive3d {
+                            entity: *visible_entity,
+                            draw_function: draw_transmissive_pbr,
+                            pipeline: pipeline_id,
+                            distance,
+                            batch_range: 0..1,
+                            dynamic_offset: None,
+                        });
+                    } else if forward {
                         alpha_mask_phase.add(AlphaMask3d {
                             entity: *visible_entity,
                             draw_function: draw_alpha_mask_pbr,
@@ -688,6 +750,11 @@ pub struct MaterialProperties {
     /// for meshes with equal depth, to avoid z-fighting.
     /// The bias is in depth-texture units so large values may be needed to overcome small depth differences.
     pub depth_bias: f32,
+    /// Whether the material would like to read from [`ViewTransmissionTexture`](bevy_core_pipeline::core_3d::ViewTransmissionTexture).
+    ///
+    /// This allows taking color output from the [`Opaque3d`] pass as an input, (for screen-space transmission) but requires
+    /// rendering to take place in a separate [`Transmissive3d`] pass.
+    pub reads_view_transmission_texture: bool,
 }
 
 /// Data prepared for a [`Material`] instance.
@@ -863,6 +930,7 @@ fn prepare_material<M: Material>(
         properties: MaterialProperties {
             alpha_mode: material.alpha_mode(),
             depth_bias: material.depth_bias(),
+            reads_view_transmission_texture: material.reads_view_transmission_texture(),
             render_method: method,
         },
     })

crates/bevy_pbr/src/pbr_material.rs

@@ -138,6 +138,152 @@ pub struct StandardMaterial {
     #[doc(alias = "specular_intensity")]
     pub reflectance: f32,
 
+    /// The amount of light transmitted _diffusely_ through the material (i.e. “translucency”)
+    ///
+    /// Implemented as a second, flipped [Lambertian diffuse](https://en.wikipedia.org/wiki/Lambertian_reflectance) lobe,
+    /// which provides an inexpensive but plausible approximation of translucency for thin dieletric objects (e.g. paper,
+    /// leaves, some fabrics) or thicker volumetric materials with short scattering distances (e.g. porcelain, wax).
+    ///
+    /// For specular transmission usecases with refraction (e.g. glass) use the [`StandardMaterial::specular_transmission`] and
+    /// [`StandardMaterial::ior`] properties instead.
+    ///
+    /// - When set to `0.0` (the default) no diffuse light is transmitted;
+    /// - When set to `1.0` all diffuse light is transmitted through the material;
+    /// - Values higher than `0.5` will cause more diffuse light to be transmitted than reflected, resulting in a “darker”
+    ///   appearance on the side facing the light than the opposite side. (e.g. plant leaves)
+    ///
+    /// ## Notes
+    ///
+    /// - The material's [`StandardMaterial::base_color`] also modulates the transmitted light;
+    /// - To receive transmitted shadows on the diffuse transmission lobe (i.e. the “backside”) of the material,
+    ///   use the [`TransmittedShadowReceiver`] component.
+    #[doc(alias = "translucency")]
+    pub diffuse_transmission: f32,
+
+    /// A map that modulates diffuse transmission via its alpha channel. Multiplied by [`StandardMaterial::diffuse_transmission`]
+    /// to obtain the final result.
+    ///
+    /// **Important:** The [`StandardMaterial::diffuse_transmission`] property must be set to a value higher than 0.0,
+    /// or this texture won't have any effect.
+    #[texture(17)]
+    #[sampler(18)]
+    #[cfg(feature = "pbr_transmission_textures")]
+    pub diffuse_transmission_texture: Option<Handle<Image>>,
+
+    /// The amount of light transmitted _specularly_ through the material (i.e. via refraction)
+    ///
+    /// - When set to `0.0` (the default) no light is transmitted.
+    /// - When set to `1.0` all light is transmitted through the material.
+    ///
+    /// The material's [`StandardMaterial::base_color`] also modulates the transmitted light.
+    ///
+    /// **Note:** Typically used in conjunction with [`StandardMaterial::thickness`], [`StandardMaterial::ior`] and [`StandardMaterial::perceptual_roughness`].
+    ///
+    /// ## Performance
+    ///
+    /// Specular transmission is implemented as a relatively expensive screen-space effect that allows ocluded objects to be seen through the material,
+    /// with distortion and blur effects.
+    ///
+    /// - [`Camera3d::screen_space_specular_transmission_steps`](bevy_core_pipeline::core_3d::Camera3d::screen_space_specular_transmission_steps) can be used to enable transmissive objects
+    /// to be seen through other transmissive objects, at the cost of additional draw calls and texture copies; (Use with caution!)
+    ///     - If a simplified approximation of specular transmission using only environment map lighting is sufficient, consider setting
+    /// [`Camera3d::screen_space_specular_transmission_steps`](bevy_core_pipeline::core_3d::Camera3d::screen_space_specular_transmission_steps) to `0`.
+    /// - If purely diffuse light transmission is needed, (i.e. “translucency”) consider using [`StandardMaterial::diffuse_transmission`] instead,
+    /// for a much less expensive effect.
+    /// - Specular transmission is rendered before alpha blending, so any material with [`AlphaMode::Blend`], [`AlphaMode::Premultiplied`], [`AlphaMode::Add`] or [`AlphaMode::Multiply`]
+    ///   won't be visible through specular transmissive materials.
+    #[doc(alias = "refraction")]
+    pub specular_transmission: f32,
+
+    /// A map that modulates specular transmission via its red channel. Multiplied by [`StandardMaterial::specular_transmission`]
+    /// to obtain the final result.
+    ///
+    /// **Important:** The [`StandardMaterial::specular_transmission`] property must be set to a value higher than 0.0,
+    /// or this texture won't have any effect.
+    #[texture(13)]
+    #[sampler(14)]
+    #[cfg(feature = "pbr_transmission_textures")]
+    pub specular_transmission_texture: Option<Handle<Image>>,
+
+    /// Thickness of the volume beneath the material surface.
+    ///
+    /// When set to `0.0` (the default) the material appears as an infinitely-thin film,
+    /// transmitting light without distorting it.
+    ///
+    /// When set to any other value, the material distorts light like a thick lens.
+    ///
+    /// **Note:** Typically used in conjunction with [`StandardMaterial::specular_transmission`] and [`StandardMaterial::ior`], or with
+    /// [`StandardMaterial::diffuse_transmission`].
+    #[doc(alias = "volume")]
+    #[doc(alias = "thin_walled")]
+    pub thickness: f32,
+
+    /// A map that modulates thickness via its green channel. Multiplied by [`StandardMaterial::thickness`]
+    /// to obtain the final result.
+    ///
+    /// **Important:** The [`StandardMaterial::thickness`] property must be set to a value higher than 0.0,
+    /// or this texture won't have any effect.
+    #[texture(15)]
+    #[sampler(16)]
+    #[cfg(feature = "pbr_transmission_textures")]
+    pub thickness_texture: Option<Handle<Image>>,
+
+    /// The [index of refraction](https://en.wikipedia.org/wiki/Refractive_index) of the material.
+    ///
+    /// Defaults to 1.5.
+    ///
+    /// | Material        | Index of Refraction  |
+    /// |:----------------|:---------------------|
+    /// | Vacuum          | 1                    |
+    /// | Air             | 1.00                 |
+    /// | Ice             | 1.31                 |
+    /// | Water           | 1.33                 |
+    /// | Eyes            | 1.38                 |
+    /// | Quartz          | 1.46                 |
+    /// | Olive Oil       | 1.47                 |
+    /// | Honey           | 1.49                 |
+    /// | Acrylic         | 1.49                 |
+    /// | Window Glass    | 1.52                 |
+    /// | Polycarbonate   | 1.58                 |
+    /// | Flint Glass     | 1.69                 |
+    /// | Ruby            | 1.71                 |
+    /// | Glycerine       | 1.74                 |
+    /// | Saphire         | 1.77                 |
+    /// | Cubic Zirconia  | 2.15                 |
+    /// | Diamond         | 2.42                 |
+    /// | Moissanite      | 2.65                 |
+    ///
+    /// **Note:** Typically used in conjunction with [`StandardMaterial::specular_transmission`] and [`StandardMaterial::thickness`].
+    #[doc(alias = "index_of_refraction")]
+    #[doc(alias = "refraction_index")]
+    #[doc(alias = "refractive_index")]
+    pub ior: f32,
+
+    /// How far, on average, light travels through the volume beneath the material's
+    /// surface before being absorbed.
+    ///
+    /// Defaults to [`f32::INFINITY`], i.e. light is never absorbed.
+    ///
+    /// **Note:** To have any effect, must be used in conjunction with:
+    /// - [`StandardMaterial::attenuation_color`];
+    /// - [`StandardMaterial::thickness`];
+    /// - [`StandardMaterial::diffuse_transmission`] or [`StandardMaterial::specular_transmission`].
+    #[doc(alias = "absorption_distance")]
+    #[doc(alias = "extinction_distance")]
+    pub attenuation_distance: f32,
+
+    /// The resulting (non-absorbed) color after white light travels through the attenuation distance.
+    ///
+    /// Defaults to [`Color::WHITE`], i.e. no change.
+    ///
+    /// **Note:** To have any effect, must be used in conjunction with:
+    /// - [`StandardMaterial::attenuation_distance`];
+    /// - [`StandardMaterial::thickness`];
+    /// - [`StandardMaterial::diffuse_transmission`] or [`StandardMaterial::specular_transmission`].
+    #[doc(alias = "absorption_color")]
+    #[doc(alias = "extinction_color")]
+    pub attenuation_color: Color,
+
     /// Used to fake the lighting of bumps and dents on a material.
     ///
     /// A typical usage would be faking cobblestones on a flat plane mesh in 3D.
@@ -343,6 +489,18 @@ impl Default for StandardMaterial {
             // Expressed in a linear scale and equivalent to 4% reflectance see
             // <https://google.github.io/filament/Material%20Properties.pdf>
             reflectance: 0.5,
+            diffuse_transmission: 0.0,
+            #[cfg(feature = "pbr_transmission_textures")]
+            diffuse_transmission_texture: None,
+            specular_transmission: 0.0,
+            #[cfg(feature = "pbr_transmission_textures")]
+            specular_transmission_texture: None,
+            thickness: 0.0,
+            #[cfg(feature = "pbr_transmission_textures")]
+            thickness_texture: None,
+            ior: 1.5,
+            attenuation_color: Color::WHITE,
+            attenuation_distance: f32::INFINITY,
             occlusion_texture: None,
             normal_map_texture: None,
             flip_normal_map_y: false,
@@ -401,6 +559,10 @@ bitflags::bitflags! {
         const FLIP_NORMAL_MAP_Y          = (1 << 7);
         const FOG_ENABLED                = (1 << 8);
         const DEPTH_MAP                  = (1 << 9); // Used for parallax mapping
+        const SPECULAR_TRANSMISSION_TEXTURE = (1 << 10);
+        const THICKNESS_TEXTURE          = (1 << 11);
+        const DIFFUSE_TRANSMISSION_TEXTURE = (1 << 12);
+        const ATTENUATION_ENABLED        = (1 << 13);
         const ALPHA_MODE_RESERVED_BITS   = (Self::ALPHA_MODE_MASK_BITS << Self::ALPHA_MODE_SHIFT_BITS); // ← Bitmask reserving bits for the `AlphaMode`
         const ALPHA_MODE_OPAQUE          = (0 << Self::ALPHA_MODE_SHIFT_BITS);                          // ← Values are just sequential values bitshifted into
         const ALPHA_MODE_MASK            = (1 << Self::ALPHA_MODE_SHIFT_BITS);                          //   the bitmask, and can range from 0 to 7.
@@ -435,6 +597,18 @@ pub struct StandardMaterialUniform {
     /// Specular intensity for non-metals on a linear scale of [0.0, 1.0]
     /// defaults to 0.5 which is mapped to 4% reflectance in the shader
     pub reflectance: f32,
+    /// Amount of diffuse light transmitted through the material
+    pub diffuse_transmission: f32,
+    /// Amount of specular light transmitted through the material
+    pub specular_transmission: f32,
+    /// Thickness of the volume underneath the material surface
+    pub thickness: f32,
+    /// Index of Refraction
+    pub ior: f32,
+    /// How far light travels through the volume underneath the material surface before being absorbed
+    pub attenuation_distance: f32,
+    /// Color white light takes after travelling through the attenuation distance underneath the material surface
+    pub attenuation_color: Vec4,
     /// The [`StandardMaterialFlags`] accessible in the `wgsl` shader.
     pub flags: u32,
     /// When the alpha mode mask flag is set, any base color alpha above this cutoff means fully opaque,
@@ -481,6 +655,18 @@ impl AsBindGroupShaderType<StandardMaterialUniform> for StandardMaterial {
         if self.depth_map.is_some() {
             flags |= StandardMaterialFlags::DEPTH_MAP;
         }
+        #[cfg(feature = "pbr_transmission_textures")]
+        {
+            if self.specular_transmission_texture.is_some() {
+                flags |= StandardMaterialFlags::SPECULAR_TRANSMISSION_TEXTURE;
+            }
+            if self.thickness_texture.is_some() {
+                flags |= StandardMaterialFlags::THICKNESS_TEXTURE;
+            }
+            if self.diffuse_transmission_texture.is_some() {
+                flags |= StandardMaterialFlags::DIFFUSE_TRANSMISSION_TEXTURE;
+            }
+        }
         let has_normal_map = self.normal_map_texture.is_some();
         if has_normal_map {
             let normal_map_id = self.normal_map_texture.as_ref().map(|h| h.id()).unwrap();
@@ -514,12 +700,22 @@ impl AsBindGroupShaderType<StandardMaterialUniform> for StandardMaterial {
             AlphaMode::Multiply => flags |= StandardMaterialFlags::ALPHA_MODE_MULTIPLY,
         };
 
+        if self.attenuation_distance.is_finite() {
+            flags |= StandardMaterialFlags::ATTENUATION_ENABLED;
+        }
+
         StandardMaterialUniform {
             base_color: self.base_color.as_linear_rgba_f32().into(),
             emissive: self.emissive.as_linear_rgba_f32().into(),
             roughness: self.perceptual_roughness,
             metallic: self.metallic,
             reflectance: self.reflectance,
+            diffuse_transmission: self.diffuse_transmission,
+            specular_transmission: self.specular_transmission,
+            thickness: self.thickness,
+            ior: self.ior,
+            attenuation_distance: self.attenuation_distance,
+            attenuation_color: self.attenuation_color.as_linear_rgba_f32().into(),
             flags: flags.bits(),
             alpha_cutoff,
             parallax_depth_scale: self.parallax_depth_scale,
@@ -602,8 +798,25 @@ impl Material for StandardMaterial {
         self.depth_bias
     }
 
+    #[inline]
+    fn reads_view_transmission_texture(&self) -> bool {
+        self.specular_transmission > 0.0
+    }
+
     #[inline]
     fn opaque_render_method(&self) -> OpaqueRendererMethod {
-        self.opaque_render_method
+        match self.opaque_render_method {
+            // For now, diffuse transmission doesn't work under deferred rendering as we don't pack
+            // the required data into the GBuffer. If this material is set to `Auto`, we report it as
+            // `Forward` so that it's rendered correctly, even when the `DefaultOpaqueRendererMethod`
+            // is set to `Deferred`.
+            //
+            // If the developer explicitly sets the `OpaqueRendererMethod` to `Deferred`, we assume
+            // they know what they're doing and don't override it.
+            OpaqueRendererMethod::Auto if self.diffuse_transmission > 0.0 => {
+                OpaqueRendererMethod::Forward
+            }
+            other => other,
+        }
     }
 }

crates/bevy_pbr/src/prepass/mod.rs

@@ -818,6 +818,12 @@ pub fn queue_prepass_material_meshes<M: Material>(
                 | AlphaMode::Multiply => continue,
             }
 
+            if material.properties.reads_view_transmission_texture {
+                // No-op: Materials reading from `ViewTransmissionTexture` are not rendered in the `Opaque3d`
+                // phase, and are therefore also excluded from the prepass much like alpha-blended materials.
+                continue;
+            }
+
             let forward = match material.properties.render_method {
                 OpaqueRendererMethod::Forward => true,
                 OpaqueRendererMethod::Deferred => false,

crates/bevy_pbr/src/prepass/prepass_utils.wgsl

@@ -5,11 +5,10 @@
 #ifdef DEPTH_PREPASS
 fn prepass_depth(frag_coord: vec4<f32>, sample_index: u32) -> f32 {
 #ifdef MULTISAMPLED
-    let depth_sample = textureLoad(view_bindings::depth_prepass_texture, vec2<i32>(frag_coord.xy), i32(sample_index));
-#else
-    let depth_sample = textureLoad(view_bindings::depth_prepass_texture, vec2<i32>(frag_coord.xy), 0);
-#endif
-    return depth_sample;
+    return textureLoad(view_bindings::depth_prepass_texture, vec2<i32>(frag_coord.xy), i32(sample_index));
+#else // MULTISAMPLED
+    return textureLoad(view_bindings::depth_prepass_texture, vec2<i32>(frag_coord.xy), 0);
+#endif // MULTISAMPLED
 }
 #endif // DEPTH_PREPASS
 

crates/bevy_pbr/src/render/mesh.rs

@@ -1,7 +1,7 @@
 use bevy_app::{Plugin, PostUpdate};
 use bevy_asset::{load_internal_asset, AssetId, Handle};
 use bevy_core_pipeline::{
-    core_3d::{AlphaMask3d, Opaque3d, Transparent3d, CORE_3D_DEPTH_FORMAT},
+    core_3d::{AlphaMask3d, Opaque3d, Transmissive3d, Transparent3d, CORE_3D_DEPTH_FORMAT},
     deferred::{AlphaMask3dDeferred, Opaque3dDeferred},
 };
 use bevy_derive::{Deref, DerefMut};
@@ -132,6 +132,7 @@ impl Plugin for MeshRenderPlugin {
                     (
                         (
                             batch_and_prepare_render_phase::<Opaque3d, MeshPipeline>,
+                            batch_and_prepare_render_phase::<Transmissive3d, MeshPipeline>,
                             batch_and_prepare_render_phase::<Transparent3d, MeshPipeline>,
                             batch_and_prepare_render_phase::<AlphaMask3d, MeshPipeline>,
                             batch_and_prepare_render_phase::<Shadow, MeshPipeline>,
@@ -221,12 +222,13 @@ impl From<&MeshTransforms> for MeshUniform {
 bitflags::bitflags! {
     #[repr(transparent)]
     pub struct MeshFlags: u32 {
-        const SHADOW_RECEIVER            = (1 << 0);
+        const SHADOW_RECEIVER             = (1 << 0);
+        const TRANSMITTED_SHADOW_RECEIVER = (1 << 1);
         // Indicates the sign of the determinant of the 3x3 model matrix. If the sign is positive,
         // then the flag should be set, else it should not be set.
-        const SIGN_DETERMINANT_MODEL_3X3 = (1 << 31);
-        const NONE                       = 0;
-        const UNINITIALIZED              = 0xFFFF;
+        const SIGN_DETERMINANT_MODEL_3X3  = (1 << 31);
+        const NONE                        = 0;
+        const UNINITIALIZED               = 0xFFFF;
     }
 }
 
@@ -257,6 +259,7 @@ pub fn extract_meshes(
             Option<&PreviousGlobalTransform>,
             &Handle<Mesh>,
             Has<NotShadowReceiver>,
+            Has<TransmittedShadowReceiver>,
             Has<NotShadowCaster>,
             Has<NoAutomaticBatching>,
         )>,
@@ -270,6 +273,7 @@ pub fn extract_meshes(
             previous_transform,
             handle,
             not_receiver,
+            transmitted_receiver,
             not_caster,
             no_automatic_batching,
         )| {
@@ -283,6 +287,9 @@ pub fn extract_meshes(
             } else {
                 MeshFlags::SHADOW_RECEIVER
             };
+            if transmitted_receiver {
+                flags |= MeshFlags::TRANSMITTED_SHADOW_RECEIVER;
+            }
             if transform.matrix3.determinant().is_sign_positive() {
                 flags |= MeshFlags::SIGN_DETERMINANT_MODEL_3X3;
             }
@@ -487,7 +494,7 @@ bitflags::bitflags! {
         const ENVIRONMENT_MAP                   = (1 << 8);
         const SCREEN_SPACE_AMBIENT_OCCLUSION    = (1 << 9);
         const DEPTH_CLAMP_ORTHO                 = (1 << 10);
-        const TAA                               = (1 << 11);
+        const TEMPORAL_JITTER                   = (1 << 11);
         const MORPH_TARGETS                     = (1 << 12);
         const BLEND_RESERVED_BITS               = Self::BLEND_MASK_BITS << Self::BLEND_SHIFT_BITS; // ← Bitmask reserving bits for the blend state
         const BLEND_OPAQUE                      = (0 << Self::BLEND_SHIFT_BITS);                   // ← Values are just sequential within the mask, and can range from 0 to 3
@@ -514,6 +521,11 @@ bitflags::bitflags! {
         const VIEW_PROJECTION_PERSPECTIVE       = 1 << Self::VIEW_PROJECTION_SHIFT_BITS;
         const VIEW_PROJECTION_ORTHOGRAPHIC      = 2 << Self::VIEW_PROJECTION_SHIFT_BITS;
         const VIEW_PROJECTION_RESERVED          = 3 << Self::VIEW_PROJECTION_SHIFT_BITS;
+        const SCREEN_SPACE_SPECULAR_TRANSMISSION_RESERVED_BITS = Self::SCREEN_SPACE_SPECULAR_TRANSMISSION_MASK_BITS << Self::SCREEN_SPACE_SPECULAR_TRANSMISSION_SHIFT_BITS;
+        const SCREEN_SPACE_SPECULAR_TRANSMISSION_LOW = 0 << Self::SCREEN_SPACE_SPECULAR_TRANSMISSION_SHIFT_BITS;
+        const SCREEN_SPACE_SPECULAR_TRANSMISSION_MEDIUM = 1 << Self::SCREEN_SPACE_SPECULAR_TRANSMISSION_SHIFT_BITS;
+        const SCREEN_SPACE_SPECULAR_TRANSMISSION_HIGH = 2 << Self::SCREEN_SPACE_SPECULAR_TRANSMISSION_SHIFT_BITS;
+        const SCREEN_SPACE_SPECULAR_TRANSMISSION_ULTRA = 3 << Self::SCREEN_SPACE_SPECULAR_TRANSMISSION_SHIFT_BITS;
     }
 }
 
@@ -541,6 +553,10 @@ impl MeshPipelineKey {
     const VIEW_PROJECTION_SHIFT_BITS: u32 =
         Self::SHADOW_FILTER_METHOD_SHIFT_BITS - Self::VIEW_PROJECTION_MASK_BITS.count_ones();
 
+    const SCREEN_SPACE_SPECULAR_TRANSMISSION_MASK_BITS: u32 = 0b11;
+    const SCREEN_SPACE_SPECULAR_TRANSMISSION_SHIFT_BITS: u32 = Self::VIEW_PROJECTION_SHIFT_BITS
+        - Self::SCREEN_SPACE_SPECULAR_TRANSMISSION_MASK_BITS.count_ones();
+
     pub fn from_msaa_samples(msaa_samples: u32) -> Self {
         let msaa_bits =
             (msaa_samples.trailing_zeros() & Self::MSAA_MASK_BITS) << Self::MSAA_SHIFT_BITS;
@@ -661,6 +677,10 @@ impl SpecializedMeshPipeline for MeshPipeline {
             vertex_attributes.push(Mesh::ATTRIBUTE_COLOR.at_shader_location(5));
         }
 
+        if cfg!(feature = "pbr_transmission_textures") {
+            shader_defs.push("PBR_TRANSMISSION_TEXTURES_SUPPORTED".into());
+        }
+
         let mut bind_group_layout = vec![self.get_view_layout(key.into()).clone()];
 
         if key.msaa_samples() > 1 {
@@ -794,8 +814,8 @@ impl SpecializedMeshPipeline for MeshPipeline {
             shader_defs.push("ENVIRONMENT_MAP".into());
         }
 
-        if key.contains(MeshPipelineKey::TAA) {
-            shader_defs.push("TAA".into());
+        if key.contains(MeshPipelineKey::TEMPORAL_JITTER) {
+            shader_defs.push("TEMPORAL_JITTER".into());
         }
 
         let shadow_filter_method =
@@ -808,6 +828,20 @@ impl SpecializedMeshPipeline for MeshPipeline {
             shader_defs.push("SHADOW_FILTER_METHOD_JIMENEZ_14".into());
         }
 
+        let blur_quality =
+            key.intersection(MeshPipelineKey::SCREEN_SPACE_SPECULAR_TRANSMISSION_RESERVED_BITS);
+
+        shader_defs.push(ShaderDefVal::Int(
+            "SCREEN_SPACE_SPECULAR_TRANSMISSION_BLUR_TAPS".into(),
+            match blur_quality {
+                MeshPipelineKey::SCREEN_SPACE_SPECULAR_TRANSMISSION_LOW => 4,
+                MeshPipelineKey::SCREEN_SPACE_SPECULAR_TRANSMISSION_MEDIUM => 8,
+                MeshPipelineKey::SCREEN_SPACE_SPECULAR_TRANSMISSION_HIGH => 16,
+                MeshPipelineKey::SCREEN_SPACE_SPECULAR_TRANSMISSION_ULTRA => 32,
+                _ => unreachable!(), // Not possible, since the mask is 2 bits, and we've covered all 4 cases
+            },
+        ));
+
         let format = if key.contains(MeshPipelineKey::HDR) {
             ViewTarget::TEXTURE_FORMAT_HDR
         } else {

crates/bevy_pbr/src/render/mesh_types.wgsl

@@ -29,5 +29,6 @@ struct MorphWeights {
 #endif
 
 const MESH_FLAGS_SHADOW_RECEIVER_BIT: u32 = 1u;
+const MESH_FLAGS_TRANSMITTED_SHADOW_RECEIVER_BIT: u32 = 2u;
 // 2^31 - if the flag is set, the sign is positive, else it is negative
 const MESH_FLAGS_SIGN_DETERMINANT_MODEL_3X3_BIT: u32 = 2147483648u;

crates/bevy_pbr/src/render/mesh_view_bindings.rs

@@ -1,6 +1,7 @@
 use std::array;
 
 use bevy_core_pipeline::{
+    core_3d::ViewTransmissionTexture,
     prepass::ViewPrepassTextures,
     tonemapping::{
         get_lut_bind_group_layout_entries, get_lut_bindings, Tonemapping, TonemappingLuts,
@@ -20,7 +21,7 @@ use bevy_render::{
         TextureFormat, TextureSampleType, TextureViewDimension,
     },
     renderer::RenderDevice,
-    texture::{BevyDefault, FallbackImageCubemap, FallbackImageMsaa, Image},
+    texture::{BevyDefault, FallbackImageCubemap, FallbackImageMsaa, FallbackImageZero, Image},
     view::{Msaa, ViewUniform, ViewUniforms},
 };
 
@@ -295,6 +296,7 @@ fn layout_entries(
     let tonemapping_lut_entries = get_lut_bind_group_layout_entries([15, 16]);
     entries.extend_from_slice(&tonemapping_lut_entries);
 
+    // Prepass
     if cfg!(any(not(feature = "webgl"), not(target_arch = "wasm32")))
         || (cfg!(all(feature = "webgl", target_arch = "wasm32"))
             && !layout_key.contains(MeshPipelineViewLayoutKey::MULTISAMPLED))
@@ -305,6 +307,26 @@ fn layout_entries(
         ));
     }
 
+    // View Transmission Texture
+    entries.extend_from_slice(&[
+        BindGroupLayoutEntry {
+            binding: 21,
+            visibility: ShaderStages::FRAGMENT,
+            ty: BindingType::Texture {
+                sample_type: TextureSampleType::Float { filterable: true },
+                multisampled: false,
+                view_dimension: TextureViewDimension::D2,
+            },
+            count: None,
+        },
+        BindGroupLayoutEntry {
+            binding: 22,
+            visibility: ShaderStages::FRAGMENT,
+            ty: BindingType::Sampler(SamplerBindingType::Filtering),
+            count: None,
+        },
+    ]);
+
     entries
 }
 
@@ -356,13 +378,15 @@ pub fn prepare_mesh_view_bind_groups(
         &ViewClusterBindings,
         Option<&ScreenSpaceAmbientOcclusionTextures>,
         Option<&ViewPrepassTextures>,
+        Option<&ViewTransmissionTexture>,
         Option<&EnvironmentMapLight>,
         &Tonemapping,
     )>,
-    (images, mut fallback_images, fallback_cubemap): (
+    (images, mut fallback_images, fallback_cubemap, fallback_image_zero): (
         Res<RenderAssets<Image>>,
         FallbackImageMsaa,
         Res<FallbackImageCubemap>,
+        Res<FallbackImageZero>,
     ),
     msaa: Res<Msaa>,
     globals_buffer: Res<GlobalsBuffer>,
@@ -387,6 +411,7 @@ pub fn prepare_mesh_view_bind_groups(
             cluster_bindings,
             ssao_textures,
             prepass_textures,
+            transmission_texture,
             environment_map,
             tonemapping,
         ) in &views
@@ -443,7 +468,18 @@ pub fn prepare_mesh_view_bind_groups(
                 {
                     entries = entries.extend_with_indices(((index, binding),));
                 }
-            }
+            };
+
+            let transmission_view = transmission_texture
+                .map(|transmission| &transmission.view)
+                .unwrap_or(&fallback_image_zero.texture_view);
+
+            let transmission_sampler = transmission_texture
+                .map(|transmission| &transmission.sampler)
+                .unwrap_or(&fallback_image_zero.sampler);
+
+            entries =
+                entries.extend_with_indices(((21, transmission_view), (22, transmission_sampler)));
 
             commands.entity(entity).insert(MeshViewBindGroup {
                 value: render_device.create_bind_group("mesh_view_bind_group", layout, &entries),

crates/bevy_pbr/src/render/mesh_view_bindings.wgsl

@@ -44,7 +44,6 @@
 @group(0) @binding(16) var dt_lut_sampler: sampler;
 
 #ifdef MULTISAMPLED
-
 #ifdef DEPTH_PREPASS
 @group(0) @binding(17) var depth_prepass_texture: texture_depth_multisampled_2d;
 #endif // DEPTH_PREPASS
@@ -72,3 +71,6 @@
 #ifdef DEFERRED_PREPASS
 @group(0) @binding(20) var deferred_prepass_texture: texture_2d<u32>;
 #endif // DEFERRED_PREPASS
+
+@group(0) @binding(21) var view_transmission_texture: texture_2d<f32>;
+@group(0) @binding(22) var view_transmission_sampler: sampler;

crates/bevy_pbr/src/render/pbr_bindings.wgsl

@@ -15,3 +15,11 @@
 @group(1) @binding(10) var normal_map_sampler: sampler;
 @group(1) @binding(11) var depth_map_texture: texture_2d<f32>;
 @group(1) @binding(12) var depth_map_sampler: sampler;
+#ifdef PBR_TRANSMISSION_TEXTURES_SUPPORTED
+@group(1) @binding(13) var specular_transmission_texture: texture_2d<f32>;
+@group(1) @binding(14) var specular_transmission_sampler: sampler;
+@group(1) @binding(15) var thickness_texture: texture_2d<f32>;
+@group(1) @binding(16) var thickness_sampler: sampler;
+@group(1) @binding(17) var diffuse_transmission_texture: texture_2d<f32>;
+@group(1) @binding(18) var diffuse_transmission_sampler: sampler;
+#endif

crates/bevy_pbr/src/render/pbr_fragment.wgsl

@@ -100,11 +100,13 @@ fn pbr_input_from_standard_material(
 
     // NOTE: Unlit bit not set means == 0 is true, so the true case is if lit
     if ((pbr_bindings::material.flags & pbr_types::STANDARD_MATERIAL_FLAGS_UNLIT_BIT) == 0u) {
-
         pbr_input.material.reflectance = pbr_bindings::material.reflectance;
+        pbr_input.material.ior = pbr_bindings::material.ior;
+        pbr_input.material.attenuation_color = pbr_bindings::material.attenuation_color;
+        pbr_input.material.attenuation_distance = pbr_bindings::material.attenuation_distance;
         pbr_input.material.alpha_cutoff = pbr_bindings::material.alpha_cutoff;
 
-        // emissive       
+        // emissive
         // TODO use .a for exposure compensation in HDR
         var emissive: vec4<f32> = pbr_bindings::material.emissive;
 #ifdef VERTEX_UVS
@@ -128,6 +130,34 @@ fn pbr_input_from_standard_material(
         pbr_input.material.metallic = metallic;
         pbr_input.material.perceptual_roughness = perceptual_roughness;
 
+        var specular_transmission: f32 = pbr_bindings::material.specular_transmission;
+#ifdef PBR_TRANSMISSION_TEXTURES_SUPPORTED
+        if ((pbr_bindings::material.flags & pbr_types::STANDARD_MATERIAL_FLAGS_SPECULAR_TRANSMISSION_TEXTURE_BIT) != 0u) {
+            specular_transmission *= textureSample(pbr_bindings::specular_transmission_texture, pbr_bindings::specular_transmission_sampler, uv).r;
+        }
+#endif
+        pbr_input.material.specular_transmission = specular_transmission;
+
+        var thickness: f32 = pbr_bindings::material.thickness;
+#ifdef PBR_TRANSMISSION_TEXTURES_SUPPORTED
+        if ((pbr_bindings::material.flags & pbr_types::STANDARD_MATERIAL_FLAGS_THICKNESS_TEXTURE_BIT) != 0u) {
+            thickness *= textureSample(pbr_bindings::thickness_texture, pbr_bindings::thickness_sampler, uv).g;
+        }
+#endif
+        // scale thickness, accounting for non-uniform scaling (e.g. a “squished” mesh)
+        thickness *= length(
+            (transpose(mesh[in.instance_index].model) * vec4(pbr_input.N, 0.0)).xyz
+        );
+        pbr_input.material.thickness = thickness;
+
+        var diffuse_transmission = pbr_bindings::material.diffuse_transmission;
+#ifdef PBR_TRANSMISSION_TEXTURES_SUPPORTED
+        if ((pbr_bindings::material.flags & pbr_types::STANDARD_MATERIAL_FLAGS_DIFFUSE_TRANSMISSION_TEXTURE_BIT) != 0u) {
+            diffuse_transmission *= textureSample(pbr_bindings::diffuse_transmission_texture, pbr_bindings::diffuse_transmission_sampler, uv).a;
+        }
+#endif
+        pbr_input.material.diffuse_transmission = diffuse_transmission;
+
         // occlusion
         // TODO: Split into diffuse/specular occlusion?
         var occlusion: vec3<f32> = vec3(1.0);

crates/bevy_pbr/src/render/pbr_functions.wgsl

@@ -6,10 +6,12 @@
     mesh_view_bindings as view_bindings,
     mesh_view_types,
     lighting,
+    transmission,
     clustered_forward as clustering,
     shadows,
     ambient,
-    mesh_types::MESH_FLAGS_SHADOW_RECEIVER_BIT,
+    mesh_types::{MESH_FLAGS_SHADOW_RECEIVER_BIT, MESH_FLAGS_TRANSMITTED_SHADOW_RECEIVER_BIT},
+    utils::E,
 }
 
 #ifdef ENVIRONMENT_MAP
@@ -18,7 +20,6 @@
 
 #import bevy_core_pipeline::tonemapping::{screen_space_dither, powsafe, tone_mapping}
 
-
 fn alpha_discard(material: pbr_types::StandardMaterial, output_color: vec4<f32>) -> vec4<f32> {
     var color = output_color;
     let alpha_mode = material.flags & pbr_types::STANDARD_MATERIAL_FLAGS_ALPHA_MODE_RESERVED_BITS;
@@ -156,6 +157,12 @@ fn apply_pbr_lighting(
     let metallic = in.material.metallic;
     let perceptual_roughness = in.material.perceptual_roughness;
     let roughness = lighting::perceptualRoughnessToRoughness(perceptual_roughness);
+    let ior = in.material.ior;
+    let thickness = in.material.thickness;
+    let diffuse_transmission = in.material.diffuse_transmission;
+    let specular_transmission = in.material.specular_transmission;
+
+    let specular_transmissive_color = specular_transmission * in.material.base_color.rgb;
 
     let occlusion = in.occlusion;
 
@@ -167,8 +174,14 @@ fn apply_pbr_lighting(
     let reflectance = in.material.reflectance;
     let F0 = 0.16 * reflectance * reflectance * (1.0 - metallic) + output_color.rgb * metallic;
 
-    // Diffuse strength inversely related to metallicity
-    let diffuse_color = output_color.rgb * (1.0 - metallic);
+    // Diffuse strength is inversely related to metallicity, specular and diffuse transmission
+    let diffuse_color = output_color.rgb * (1.0 - metallic) * (1.0 - specular_transmission) * (1.0 - diffuse_transmission);
+
+    // Diffuse transmissive strength is inversely related to metallicity and specular transmission, but directly related to diffuse transmission
+    let diffuse_transmissive_color = output_color.rgb * (1.0 - metallic) * (1.0 - specular_transmission) * diffuse_transmission;
+
+    // Calculate the world position of the second Lambertian lobe used for diffuse transmission, by subtracting material thickness
+    let diffuse_transmissive_lobe_world_position = in.world_position - vec4<f32>(in.world_normal, 0.0) * thickness;
 
     let R = reflect(-in.V, in.N);
 
@@ -176,6 +189,9 @@ fn apply_pbr_lighting(
 
     var direct_light: vec3<f32> = vec3<f32>(0.0);
 
+    // Transmitted Light (Specular and Diffuse)
+    var transmitted_light: vec3<f32> = vec3<f32>(0.0);
+
     let view_z = dot(vec4<f32>(
         view_bindings::view.inverse_view[0].z,
         view_bindings::view.inverse_view[1].z,
@@ -195,6 +211,25 @@ fn apply_pbr_lighting(
         }
         let light_contrib = lighting::point_light(in.world_position.xyz, light_id, roughness, NdotV, in.N, in.V, R, F0, f_ab, diffuse_color);
         direct_light += light_contrib * shadow;
+
+        if diffuse_transmission > 0.0 {
+            // NOTE: We use the diffuse transmissive color, the second Lambertian lobe's calculated
+            // world position, inverted normal and view vectors, and the following simplified
+            // values for a fully diffuse transmitted light contribution approximation:
+            //
+            // roughness = 1.0;
+            // NdotV = 1.0;
+            // R = vec3<f32>(0.0) // doesn't really matter
+            // f_ab = vec2<f32>(0.1)
+            // F0 = vec3<f32>(0.0)
+            var transmitted_shadow: f32 = 1.0;
+            if ((in.flags & (MESH_FLAGS_SHADOW_RECEIVER_BIT | MESH_FLAGS_TRANSMITTED_SHADOW_RECEIVER_BIT)) == (MESH_FLAGS_SHADOW_RECEIVER_BIT | MESH_FLAGS_TRANSMITTED_SHADOW_RECEIVER_BIT)
+                    && (view_bindings::point_lights.data[light_id].flags & mesh_view_types::POINT_LIGHT_FLAGS_SHADOWS_ENABLED_BIT) != 0u) {
+                transmitted_shadow = shadows::fetch_point_shadow(light_id, diffuse_transmissive_lobe_world_position, -in.world_normal);
+            }
+            let light_contrib = lighting::point_light(diffuse_transmissive_lobe_world_position.xyz, light_id, 1.0, 1.0, -in.N, -in.V, vec3<f32>(0.0), vec3<f32>(0.0), vec2<f32>(0.1), diffuse_transmissive_color);
+            transmitted_light += light_contrib * transmitted_shadow;
+        }
     }
 
     // Spot lights (direct)
@@ -208,6 +243,25 @@ fn apply_pbr_lighting(
         }
         let light_contrib = lighting::spot_light(in.world_position.xyz, light_id, roughness, NdotV, in.N, in.V, R, F0, f_ab, diffuse_color);
         direct_light += light_contrib * shadow;
+
+        if diffuse_transmission > 0.0 {
+            // NOTE: We use the diffuse transmissive color, the second Lambertian lobe's calculated
+            // world position, inverted normal and view vectors, and the following simplified
+            // values for a fully diffuse transmitted light contribution approximation:
+            //
+            // roughness = 1.0;
+            // NdotV = 1.0;
+            // R = vec3<f32>(0.0) // doesn't really matter
+            // f_ab = vec2<f32>(0.1)
+            // F0 = vec3<f32>(0.0)
+            var transmitted_shadow: f32 = 1.0;
+            if ((in.flags & (MESH_FLAGS_SHADOW_RECEIVER_BIT | MESH_FLAGS_TRANSMITTED_SHADOW_RECEIVER_BIT)) == (MESH_FLAGS_SHADOW_RECEIVER_BIT | MESH_FLAGS_TRANSMITTED_SHADOW_RECEIVER_BIT)
+                    && (view_bindings::point_lights.data[light_id].flags & mesh_view_types::POINT_LIGHT_FLAGS_SHADOWS_ENABLED_BIT) != 0u) {
+                transmitted_shadow = shadows::fetch_spot_shadow(light_id, diffuse_transmissive_lobe_world_position, -in.world_normal);
+            }
+            let light_contrib = lighting::spot_light(diffuse_transmissive_lobe_world_position.xyz, light_id, 1.0, 1.0, -in.N, -in.V, vec3<f32>(0.0), vec3<f32>(0.0), vec2<f32>(0.1), diffuse_transmissive_color);
+            transmitted_light += light_contrib * transmitted_shadow;
+        }
     }
 
     // directional lights (direct)
@@ -223,22 +277,104 @@ fn apply_pbr_lighting(
         light_contrib = shadows::cascade_debug_visualization(light_contrib, i, view_z);
 #endif
         direct_light += light_contrib * shadow;
+
+        if diffuse_transmission > 0.0 {
+            // NOTE: We use the diffuse transmissive color, the second Lambertian lobe's calculated
+            // world position, inverted normal and view vectors, and the following simplified
+            // values for a fully diffuse transmitted light contribution approximation:
+            //
+            // roughness = 1.0;
+            // NdotV = 1.0;
+            // R = vec3<f32>(0.0) // doesn't really matter
+            // f_ab = vec2<f32>(0.1)
+            // F0 = vec3<f32>(0.0)
+            var transmitted_shadow: f32 = 1.0;
+            if ((in.flags & (MESH_FLAGS_SHADOW_RECEIVER_BIT | MESH_FLAGS_TRANSMITTED_SHADOW_RECEIVER_BIT)) == (MESH_FLAGS_SHADOW_RECEIVER_BIT | MESH_FLAGS_TRANSMITTED_SHADOW_RECEIVER_BIT)
+                    && (view_bindings::lights.directional_lights[i].flags & mesh_view_types::DIRECTIONAL_LIGHT_FLAGS_SHADOWS_ENABLED_BIT) != 0u) {
+                transmitted_shadow = shadows::fetch_directional_shadow(i, diffuse_transmissive_lobe_world_position, -in.world_normal, view_z);
+            }
+            let light_contrib = lighting::directional_light(i, 1.0, 1.0, -in.N, -in.V, vec3<f32>(0.0), vec3<f32>(0.0), vec2<f32>(0.1), diffuse_transmissive_color);
+            transmitted_light += light_contrib * transmitted_shadow;
+        }
     }
 
     // Ambient light (indirect)
     var indirect_light = ambient::ambient_light(in.world_position, in.N, in.V, NdotV, diffuse_color, F0, perceptual_roughness, occlusion);
 
+    if diffuse_transmission > 0.0 {
+        // NOTE: We use the diffuse transmissive color, the second Lambertian lobe's calculated
+        // world position, inverted normal and view vectors, and the following simplified
+        // values for a fully diffuse transmitted light contribution approximation:
+        //
+        // perceptual_roughness = 1.0;
+        // NdotV = 1.0;
+        // F0 = vec3<f32>(0.0)
+        // occlusion = vec3<f32>(1.0)
+        transmitted_light += ambient::ambient_light(diffuse_transmissive_lobe_world_position, -in.N, -in.V, 1.0, diffuse_transmissive_color, vec3<f32>(0.0), 1.0, vec3<f32>(1.0));
+    }
+
     // Environment map light (indirect)
 #ifdef ENVIRONMENT_MAP
     let environment_light = environment_map::environment_map_light(perceptual_roughness, roughness, diffuse_color, NdotV, f_ab, in.N, R, F0);
     indirect_light += (environment_light.diffuse * occlusion) + environment_light.specular;
+
+    // we'll use the specular component of the transmitted environment
+    // light in the call to `specular_transmissive_light()` below
+    var specular_transmitted_environment_light = vec3<f32>(0.0);
+
+    if diffuse_transmission > 0.0 || specular_transmission > 0.0 {
+        // NOTE: We use the diffuse transmissive color, inverted normal and view vectors,
+        // and the following simplified values for the transmitted environment light contribution
+        // approximation:
+        //
+        // diffuse_color = vec3<f32>(1.0) // later we use `diffuse_transmissive_color` and `specular_transmissive_color`
+        // NdotV = 1.0;
+        // R = T // see definition below
+        // F0 = vec3<f32>(1.0)
+        // occlusion = 1.0
+        //
+        // (This one is slightly different from the other light types above, because the environment
+        // map light returns both diffuse and specular components separately, and we want to use both)
+
+        let T = -normalize(
+            in.V + // start with view vector at entry point
+            refract(in.V, -in.N, 1.0 / ior) * thickness // add refracted vector scaled by thickness, towards exit point
+        ); // normalize to find exit point view vector
+
+        let transmitted_environment_light = bevy_pbr::environment_map::environment_map_light(perceptual_roughness, roughness, vec3<f32>(1.0), 1.0, f_ab, -in.N, T, vec3<f32>(1.0));
+        transmitted_light += transmitted_environment_light.diffuse * diffuse_transmissive_color;
+        specular_transmitted_environment_light = transmitted_environment_light.specular * specular_transmissive_color;
+    }
+#else
+    // If there's no environment map light, there's no transmitted environment
+    // light specular component, so we can just hardcode it to zero.
+    let specular_transmitted_environment_light = vec3<f32>(0.0);
 #endif
 
     let emissive_light = emissive.rgb * output_color.a;
 
+    if specular_transmission > 0.0 {
+        transmitted_light += transmission::specular_transmissive_light(in.world_position, in.frag_coord.xyz, view_z, in.N, in.V, F0, ior, thickness, perceptual_roughness, specular_transmissive_color, specular_transmitted_environment_light).rgb;
+    }
+
+    if (in.material.flags & pbr_types::STANDARD_MATERIAL_FLAGS_ATTENUATION_ENABLED_BIT) != 0u {
+        // We reuse the `atmospheric_fog()` function here, as it's fundamentally
+        // equivalent to the attenuation that takes place inside the material volume,
+        // and will allow us to eventually hook up subsurface scattering more easily
+        var attenuation_fog: mesh_view_types::Fog;
+        attenuation_fog.base_color.a = 1.0;
+        attenuation_fog.be = pow(1.0 - in.material.attenuation_color.rgb, vec3<f32>(E)) / in.material.attenuation_distance;
+        // TODO: Add the subsurface scattering factor below
+        // attenuation_fog.bi = /* ... */
+        transmitted_light = bevy_pbr::fog::atmospheric_fog(
+            attenuation_fog, vec4<f32>(transmitted_light, 1.0), thickness,
+            vec3<f32>(0.0) // TODO: Pass in (pre-attenuated) scattered light contribution here
+        ).rgb;
+    }
+
     // Total light
     output_color = vec4<f32>(
-        direct_light + indirect_light + emissive_light,
+        transmitted_light + direct_light + indirect_light + emissive_light,
         output_color.a
     );
 

crates/bevy_pbr/src/render/pbr_transmission.wgsl

@@ -0,0 +1,181 @@
+#define_import_path bevy_pbr::transmission
+
+#import bevy_pbr::{
+    lighting,
+    prepass_utils,
+    utils::{PI, interleaved_gradient_noise},
+    utils,
+    mesh_view_bindings as view_bindings,
+};
+
+#import bevy_core_pipeline::tonemapping::{
+    approximate_inverse_tone_mapping
+};
+
+fn specular_transmissive_light(world_position: vec4<f32>, frag_coord: vec3<f32>, view_z: f32, N: vec3<f32>, V: vec3<f32>, F0: vec3<f32>, ior: f32, thickness: f32, perceptual_roughness: f32, specular_transmissive_color: vec3<f32>, transmitted_environment_light_specular: vec3<f32>) -> vec3<f32> {
+    // Calculate the ratio between refaction indexes. Assume air/vacuum for the space outside the mesh
+    let eta = 1.0 / ior;
+
+    // Calculate incidence vector (opposite to view vector) and its dot product with the mesh normal
+    let I = -V;
+    let NdotI = dot(N, I);
+
+    // Calculate refracted direction using Snell's law
+    let k = 1.0 - eta * eta * (1.0 - NdotI * NdotI);
+    let T = eta * I - (eta * NdotI + sqrt(k)) * N;
+
+    // Calculate the exit position of the refracted ray, by propagating refacted direction through thickness
+    let exit_position = world_position.xyz + T * thickness;
+
+    // Transform exit_position into clip space
+    let clip_exit_position = view_bindings::view.view_proj * vec4<f32>(exit_position, 1.0);
+
+    // Scale / offset position so that coordinate is in right space for sampling transmissive background texture
+    let offset_position = (clip_exit_position.xy / clip_exit_position.w) * vec2<f32>(0.5, -0.5) + 0.5;
+
+    // Fetch background color
+    var background_color: vec4<f32>;
+    if perceptual_roughness == 0.0 {
+        // If the material has zero roughness, we can use a faster approach without the blur
+        background_color = fetch_transmissive_background_non_rough(offset_position, frag_coord);
+    } else {
+        background_color = fetch_transmissive_background(offset_position, frag_coord, view_z, perceptual_roughness);
+    }
+
+    // Dot product of the refracted direction with the exit normal (Note: We assume the exit normal is the entry normal but inverted)
+    let MinusNdotT = dot(-N, T);
+
+    // Calculate 1.0 - fresnel factor (how much light is _NOT_ reflected, i.e. how much is transmitted)
+    let F = vec3(1.0) - lighting::fresnel(F0, MinusNdotT);
+
+    // Calculate final color by applying fresnel multiplied specular transmissive color to a mix of background color and transmitted specular environment light
+    return F * specular_transmissive_color * mix(transmitted_environment_light_specular, background_color.rgb, background_color.a);
+}
+
+fn fetch_transmissive_background_non_rough(offset_position: vec2<f32>, frag_coord: vec3<f32>) -> vec4<f32> {
+    var background_color = textureSample(
+        view_bindings::view_transmission_texture,
+        view_bindings::view_transmission_sampler,
+        offset_position,
+    );
+
+#ifdef DEPTH_PREPASS
+    // Use depth prepass data to reject values that are in front of the current fragment
+    if prepass_utils::prepass_depth(vec4<f32>(offset_position * view_bindings::view.viewport.zw, 0.0, 0.0), 0u) > frag_coord.z {
+        background_color.a = 0.0;
+    }
+#endif
+
+#ifdef TONEMAP_IN_SHADER
+    background_color = approximate_inverse_tone_mapping(background_color, view_bindings::view.color_grading);
+#endif
+
+    return background_color;
+}
+
+fn fetch_transmissive_background(offset_position: vec2<f32>, frag_coord: vec3<f32>, view_z: f32, perceptual_roughness: f32) -> vec4<f32> {
+    // Calculate view aspect ratio, used to scale offset so that it's proportionate
+    let aspect = view_bindings::view.viewport.z / view_bindings::view.viewport.w;
+
+    // Calculate how “blurry” the transmission should be.
+    // Blur is more or less eyeballed to look approximately “right”, since the “correct”
+    // approach would involve projecting many scattered rays and figuring out their individual
+    // exit positions. IRL, light rays can be scattered when entering/exiting a material (due to
+    // roughness) or inside the material (due to subsurface scattering). Here, we only consider
+    // the first scenario.
+    //
+    // Blur intensity is:
+    // - proportional to the square of `perceptual_roughness`
+    // - proportional to the inverse of view z
+    let blur_intensity = (perceptual_roughness * perceptual_roughness) / view_z;
+
+#ifdef SCREEN_SPACE_SPECULAR_TRANSMISSION_BLUR_TAPS
+    let num_taps = #{SCREEN_SPACE_SPECULAR_TRANSMISSION_BLUR_TAPS}; // Controlled by the `Camera3d::screen_space_specular_transmission_quality` property
+#else
+    let num_taps = 8; // Fallback to 8 taps, if not specified
+#endif
+    let num_spirals = i32(ceil(f32(num_taps) / 8.0));
+#ifdef TEMPORAL_JITTER
+    let random_angle = interleaved_gradient_noise(frag_coord.xy, view_bindings::globals.frame_count);
+#else
+    let random_angle = interleaved_gradient_noise(frag_coord.xy, 0u);
+#endif
+    // Pixel checkerboard pattern (helps make the interleaved gradient noise pattern less visible)
+    let pixel_checkboard = (
+#ifdef TEMPORAL_JITTER
+        // 0 or 1 on even/odd pixels, alternates every frame
+        (i32(frag_coord.x) + i32(frag_coord.y) + i32(view_bindings::globals.frame_count)) % 2
+#else
+        // 0 or 1 on even/odd pixels
+        (i32(frag_coord.x) + i32(frag_coord.y)) % 2
+#endif
+    );
+
+    var result = vec4<f32>(0.0);
+    for (var i: i32 = 0; i < num_taps; i = i + 1) {
+        let current_spiral = (i >> 3u);
+        let angle = (random_angle + f32(current_spiral) / f32(num_spirals)) * 2.0 * PI;
+        let m = vec2(sin(angle), cos(angle));
+        let rotation_matrix = mat2x2(
+            m.y, -m.x,
+            m.x, m.y
+        );
+
+        // Get spiral offset
+        var spiral_offset: vec2<f32>;
+        switch i & 7 {
+            // https://www.iryoku.com/next-generation-post-processing-in-call-of-duty-advanced-warfare (slides 120-135)
+            // TODO: Figure out a more reasonable way of doing this, as WGSL
+            // seems to only allow constant indexes into constant arrays at the moment.
+            // The downstream shader compiler should be able to optimize this into a single
+            // constant when unrolling the for loop, but it's still not ideal.
+            case 0: { spiral_offset = utils::SPIRAL_OFFSET_0_; } // Note: We go even first and then odd, so that the lowest
+            case 1: { spiral_offset = utils::SPIRAL_OFFSET_2_; } // quality possible (which does 4 taps) still does a full spiral
+            case 2: { spiral_offset = utils::SPIRAL_OFFSET_4_; } // instead of just the first half of it
+            case 3: { spiral_offset = utils::SPIRAL_OFFSET_6_; }
+            case 4: { spiral_offset = utils::SPIRAL_OFFSET_1_; }
+            case 5: { spiral_offset = utils::SPIRAL_OFFSET_3_; }
+            case 6: { spiral_offset = utils::SPIRAL_OFFSET_5_; }
+            case 7: { spiral_offset = utils::SPIRAL_OFFSET_7_; }
+            default: {}
+        }
+
+        // Make each consecutive spiral slightly smaller than the previous one
+        spiral_offset *= 1.0 - (0.5 * f32(current_spiral + 1) / f32(num_spirals));
+
+        // Rotate and correct for aspect ratio
+        let rotated_spiral_offset = (rotation_matrix * spiral_offset) * vec2(1.0, aspect);
+
+        // Calculate final offset position, with blur and spiral offset
+        let modified_offset_position = offset_position + rotated_spiral_offset * blur_intensity * (1.0 - f32(pixel_checkboard) * 0.1);
+
+        // Sample the view transmission texture at the offset position + noise offset, to get the background color
+        var sample = textureSample(
+            view_bindings::view_transmission_texture,
+            view_bindings::view_transmission_sampler,
+            modified_offset_position,
+        );
+
+#ifdef DEPTH_PREPASS
+        // Use depth prepass data to reject values that are in front of the current fragment
+        if prepass_utils::prepass_depth(vec4<f32>(modified_offset_position * view_bindings::view.viewport.zw, 0.0, 0.0), 0u) > frag_coord.z {
+            sample = vec4<f32>(0.0);
+        }
+#endif
+
+        // As blur intensity grows higher, gradually limit *very bright* color RGB values towards a
+        // maximum length of 1.0 to prevent stray “firefly” pixel artifacts. This can potentially make
+        // very strong emissive meshes appear much dimmer, but the artifacts are noticeable enough to
+        // warrant this treatment.
+        let normalized_rgb = normalize(sample.rgb);
+        result += vec4(min(sample.rgb, normalized_rgb / saturate(blur_intensity / 2.0)), sample.a);
+    }
+
+    result /= f32(num_taps);
+
+#ifdef TONEMAP_IN_SHADER
+    result = approximate_inverse_tone_mapping(result, view_bindings::view.color_grading);
+#endif
+
+    return result;
+}

crates/bevy_pbr/src/render/pbr_types.wgsl

@@ -6,6 +6,12 @@ struct StandardMaterial {
     perceptual_roughness: f32,
     metallic: f32,
     reflectance: f32,
+    diffuse_transmission: f32,
+    specular_transmission: f32,
+    thickness: f32,
+    ior: f32,
+    attenuation_distance: f32,
+    attenuation_color: vec4<f32>,
     // 'flags' is a bit field indicating various options. u32 is 32 bits so we have up to 32 options.
     flags: u32,
     alpha_cutoff: f32,
@@ -30,6 +36,10 @@ const STANDARD_MATERIAL_FLAGS_TWO_COMPONENT_NORMAL_MAP: u32       = 64u;
 const STANDARD_MATERIAL_FLAGS_FLIP_NORMAL_MAP_Y: u32              = 128u;
 const STANDARD_MATERIAL_FLAGS_FOG_ENABLED_BIT: u32                = 256u;
 const STANDARD_MATERIAL_FLAGS_DEPTH_MAP_BIT: u32                  = 512u;
+const STANDARD_MATERIAL_FLAGS_SPECULAR_TRANSMISSION_TEXTURE_BIT: u32 = 1024u;
+const STANDARD_MATERIAL_FLAGS_THICKNESS_TEXTURE_BIT: u32          = 2048u;
+const STANDARD_MATERIAL_FLAGS_DIFFUSE_TRANSMISSION_TEXTURE_BIT: u32 = 4096u;
+const STANDARD_MATERIAL_FLAGS_ATTENUATION_ENABLED_BIT: u32        = 8192u;
 const STANDARD_MATERIAL_FLAGS_ALPHA_MODE_RESERVED_BITS: u32       = 3758096384u; // (0b111u32 << 29)
 const STANDARD_MATERIAL_FLAGS_ALPHA_MODE_OPAQUE: u32              = 0u;          // (0u32 << 29)
 const STANDARD_MATERIAL_FLAGS_ALPHA_MODE_MASK: u32                = 536870912u;  // (1u32 << 29)
@@ -51,6 +61,12 @@ fn standard_material_new() -> StandardMaterial {
     material.perceptual_roughness = 0.5;
     material.metallic = 0.00;
     material.reflectance = 0.5;
+    material.diffuse_transmission = 0.0;
+    material.specular_transmission = 0.0;
+    material.thickness = 0.0;
+    material.ior = 1.5;
+    material.attenuation_distance = 1.0;
+    material.attenuation_color = vec4<f32>(1.0, 1.0, 1.0, 1.0);
     material.flags = STANDARD_MATERIAL_FLAGS_ALPHA_MODE_OPAQUE;
     material.alpha_cutoff = 0.5;
     material.parallax_depth_scale = 0.1;

crates/bevy_pbr/src/render/shadow_sampling.wgsl

@@ -2,7 +2,8 @@
 
 #import bevy_pbr::{
     mesh_view_bindings as view_bindings,
-    utils::PI,
+    utils::{PI, interleaved_gradient_noise},
+    utils,
 }
 
 // Do the lookup, using HW 2x2 PCF and comparison
@@ -70,13 +71,6 @@ fn sample_shadow_map_castano_thirteen(light_local: vec2<f32>, depth: f32, array_
     return sum * (1.0 / 144.0);
 }
 
-// https://blog.demofox.org/2022/01/01/interleaved-gradient-noise-a-different-kind-of-low-discrepancy-sequence
-fn interleaved_gradient_noise(pixel_coordinates: vec2<f32>) -> f32 {
-    let frame = f32(view_bindings::globals.frame_count % 64u);
-    let xy = pixel_coordinates + 5.588238 * frame;
-    return fract(52.9829189 * fract(0.06711056 * xy.x + 0.00583715 * xy.y));
-}
-
 fn map(min1: f32, max1: f32, min2: f32, max2: f32, value: f32) -> f32 {
     return min2 + (value - min1) * (max2 - min2) / (max1 - min1);
 }
@@ -84,7 +78,7 @@ fn map(min1: f32, max1: f32, min2: f32, max2: f32, value: f32) -> f32 {
 fn sample_shadow_map_jimenez_fourteen(light_local: vec2<f32>, depth: f32, array_index: i32, texel_size: f32) -> f32 {
     let shadow_map_size = vec2<f32>(textureDimensions(view_bindings::directional_shadow_textures));
 
-    let random_angle = 2.0 * PI * interleaved_gradient_noise(light_local * shadow_map_size);
+    let random_angle = 2.0 * PI * interleaved_gradient_noise(light_local * shadow_map_size, view_bindings::globals.frame_count);
     let m = vec2(sin(random_angle), cos(random_angle));
     let rotation_matrix = mat2x2(
         m.y, -m.x,
@@ -96,14 +90,14 @@ fn sample_shadow_map_jimenez_fourteen(light_local: vec2<f32>, depth: f32, array_
     let uv_offset_scale = f / (texel_size * shadow_map_size);
 
     // https://www.iryoku.com/next-generation-post-processing-in-call-of-duty-advanced-warfare (slides 120-135)
-    let sample_offset1 = (rotation_matrix * vec2(-0.7071,  0.7071)) * uv_offset_scale;
-    let sample_offset2 = (rotation_matrix * vec2(-0.0000, -0.8750)) * uv_offset_scale;
-    let sample_offset3 = (rotation_matrix * vec2( 0.5303,  0.5303)) * uv_offset_scale;
-    let sample_offset4 = (rotation_matrix * vec2(-0.6250, -0.0000)) * uv_offset_scale;
-    let sample_offset5 = (rotation_matrix * vec2( 0.3536, -0.3536)) * uv_offset_scale;
-    let sample_offset6 = (rotation_matrix * vec2(-0.0000,  0.3750)) * uv_offset_scale;
-    let sample_offset7 = (rotation_matrix * vec2(-0.1768, -0.1768)) * uv_offset_scale;
-    let sample_offset8 = (rotation_matrix * vec2( 0.1250,  0.0000)) * uv_offset_scale;
+    let sample_offset1 = (rotation_matrix * utils::SPIRAL_OFFSET_0_) * uv_offset_scale;
+    let sample_offset2 = (rotation_matrix * utils::SPIRAL_OFFSET_1_) * uv_offset_scale;
+    let sample_offset3 = (rotation_matrix * utils::SPIRAL_OFFSET_2_) * uv_offset_scale;
+    let sample_offset4 = (rotation_matrix * utils::SPIRAL_OFFSET_3_) * uv_offset_scale;
+    let sample_offset5 = (rotation_matrix * utils::SPIRAL_OFFSET_4_) * uv_offset_scale;
+    let sample_offset6 = (rotation_matrix * utils::SPIRAL_OFFSET_5_) * uv_offset_scale;
+    let sample_offset7 = (rotation_matrix * utils::SPIRAL_OFFSET_6_) * uv_offset_scale;
+    let sample_offset8 = (rotation_matrix * utils::SPIRAL_OFFSET_7_) * uv_offset_scale;
 
     var sum = 0.0;
     sum += sample_shadow_map_hardware(light_local + sample_offset1, depth, array_index);

crates/bevy_pbr/src/render/utils.wgsl

@@ -48,3 +48,22 @@ fn octahedral_decode(v: vec2<f32>) -> vec3<f32> {
     n = vec3(n.xy + w, n.z);
     return normalize(n);
 }
+
+// https://blog.demofox.org/2022/01/01/interleaved-gradient-noise-a-different-kind-of-low-discrepancy-sequence
+fn interleaved_gradient_noise(pixel_coordinates: vec2<f32>, frame: u32) -> f32 {
+    let xy = pixel_coordinates + 5.588238 * f32(frame % 64u);
+    return fract(52.9829189 * fract(0.06711056 * xy.x + 0.00583715 * xy.y));
+}
+
+// https://www.iryoku.com/next-generation-post-processing-in-call-of-duty-advanced-warfare (slides 120-135)
+// TODO: Use an array here instead of a bunch of constants, once arrays work properly under DX12.
+// NOTE: The names have a final underscore to avoid the following error:
+// `Composable module identifiers must not require substitution according to naga writeback rules`
+const SPIRAL_OFFSET_0_ = vec2<f32>(-0.7071,  0.7071);
+const SPIRAL_OFFSET_1_ = vec2<f32>(-0.0000, -0.8750);
+const SPIRAL_OFFSET_2_ = vec2<f32>( 0.5303,  0.5303);
+const SPIRAL_OFFSET_3_ = vec2<f32>(-0.6250, -0.0000);
+const SPIRAL_OFFSET_4_ = vec2<f32>( 0.3536, -0.3536);
+const SPIRAL_OFFSET_5_ = vec2<f32>(-0.0000,  0.3750);
+const SPIRAL_OFFSET_6_ = vec2<f32>(-0.1768, -0.1768);
+const SPIRAL_OFFSET_7_ = vec2<f32>( 0.1250,  0.0000);

crates/bevy_pbr/src/ssao/gtao.wgsl

@@ -26,7 +26,7 @@
 fn load_noise(pixel_coordinates: vec2<i32>) -> vec2<f32> {
     var index = textureLoad(hilbert_index_lut, pixel_coordinates % 64, 0).r;
 
-#ifdef TEMPORAL_NOISE
+#ifdef TEMPORAL_JITTER
     index += 288u * (globals.frame_count % 64u);
 #endif
 

crates/bevy_pbr/src/ssao/mod.rs

@@ -560,7 +560,7 @@ impl FromWorld for SsaoPipelines {
 #[derive(PartialEq, Eq, Hash, Clone)]
 struct SsaoPipelineKey {
     ssao_settings: ScreenSpaceAmbientOcclusionSettings,
-    temporal_noise: bool,
+    temporal_jitter: bool,
 }
 
 impl SpecializedComputePipeline for SsaoPipelines {
@@ -577,8 +577,8 @@ impl SpecializedComputePipeline for SsaoPipelines {
             ),
         ];
 
-        if key.temporal_noise {
-            shader_defs.push("TEMPORAL_NOISE".into());
+        if key.temporal_jitter {
+            shader_defs.push("TEMPORAL_JITTER".into());
         }
 
         ComputePipelineDescriptor {
@@ -731,7 +731,7 @@ fn prepare_ssao_pipelines(
             &pipeline,
             SsaoPipelineKey {
                 ssao_settings: ssao_settings.clone(),
-                temporal_noise: temporal_jitter.is_some(),
+                temporal_jitter: temporal_jitter.is_some(),
             },
         );
 

crates/bevy_render/src/batching/mod.rs

@@ -97,7 +97,11 @@ pub fn batch_and_prepare_render_phase<I: CachedRenderPipelinePhaseItem, F: GetBa
         *item.batch_range_mut() = index..index + 1;
         *item.dynamic_offset_mut() = buffer_index.dynamic_offset;
 
-        compare_data.map(|compare_data| BatchMeta::new(item, compare_data))
+        if I::AUTOMATIC_BATCHING {
+            compare_data.map(|compare_data| BatchMeta::new(item, compare_data))
+        } else {
+            None
+        }
     };
 
     for mut phase in &mut views {

crates/bevy_render/src/render_phase/mod.rs

@@ -139,6 +139,9 @@ pub trait PhaseItem: Sized + Send + Sync + 'static {
     /// based on the view-space `Z` value of the corresponding view matrix.
     type SortKey: Ord;
 
+    /// Whether or not this `PhaseItem` should be subjected to automatic batching. (Default: `true`)
+    const AUTOMATIC_BATCHING: bool = true;
+
     /// The corresponding entity that will be drawn.
     ///
     /// This is used to fetch the render data of the entity, required by the draw function,

docs/cargo_features.md

@@ -61,6 +61,7 @@ The default feature set enables most of the expected features of a game engine,
 |jpeg|JPEG image format support|
 |minimp3|MP3 audio format support (through minimp3)|
 |mp3|MP3 audio format support|
+|pbr_transmission_textures|Enable support for transmission-related textures in the `StandardMaterial`, at the risk of blowing past the global, per-shader texture limit on older/lower-end GPUs|
 |pnm|PNM image format support, includes pam, pbm, pgm and ppm|
 |serialize|Enable serialization support through serde|
 |shader_format_glsl|Enable support for shaders in GLSL|

examples/3d/transmission.rs

@@ -0,0 +1,664 @@
+//! This example showcases light transmission
+//!
+//! ## Controls
+//!
+//! | Key Binding        | Action                                               |
+//! |:-------------------|:-----------------------------------------------------|
+//! | `J`/`K`/`L`/`;`    | Change Screen Space Transmission Quality             |
+//! | `O` / `P`          | Decrease / Increase Screen Space Transmission Steps  |
+//! | `1` / `2`          | Decrease / Increase Diffuse Transmission             |
+//! | `Q` / `W`          | Decrease / Increase Specular Transmission            |
+//! | `A` / `S`          | Decrease / Increase Thickness                        |
+//! | `Z` / `X`          | Decrease / Increase IOR                              |
+//! | `E` / `R`          | Decrease / Increase Perceptual Roughness             |
+//! | `U` / `I`          | Decrease / Increase Reflectance                      |
+//! | Arrow Keys         | Control Camera                                       |
+//! | `C`                | Randomize Colors                                     |
+//! | `H`                | Toggle HDR + Bloom                                   |
+//! | `D`                | Toggle Depth Prepass                                 |
+//! | `T`                | Toggle TAA                                           |
+
+// This lint usually gives bad advice in the context of Bevy -- hiding complex queries behind
+// type aliases tends to obfuscate code while offering no improvement in code cleanliness.
+#![allow(clippy::type_complexity)]
+
+use std::f32::consts::PI;
+
+use bevy::{
+    core_pipeline::{
+        bloom::BloomSettings, core_3d::ScreenSpaceTransmissionQuality, prepass::DepthPrepass,
+        tonemapping::Tonemapping,
+    },
+    pbr::{NotShadowCaster, PointLightShadowMap, TransmittedShadowReceiver},
+    prelude::*,
+    render::camera::TemporalJitter,
+    render::view::ColorGrading,
+};
+
+#[cfg(not(all(feature = "webgl2", target_arch = "wasm32")))]
+use bevy::core_pipeline::experimental::taa::{
+    TemporalAntiAliasBundle, TemporalAntiAliasPlugin, TemporalAntiAliasSettings,
+};
+
+use rand::random;
+
+fn main() {
+    let mut app = App::new();
+
+    app.add_plugins(DefaultPlugins)
+        .insert_resource(ClearColor(Color::BLACK))
+        .insert_resource(PointLightShadowMap { size: 2048 })
+        .insert_resource(AmbientLight {
+            brightness: 0.0,
+            ..default()
+        })
+        .add_systems(Startup, setup)
+        .add_systems(Update, (example_control_system, flicker_system));
+
+    // *Note:* TAA is not _required_ for specular transmission, but
+    // it _greatly enhances_ the look of the resulting blur effects.
+    // Sadly, it's not available under WebGL.
+    #[cfg(not(all(feature = "webgl2", target_arch = "wasm32")))]
+    app.insert_resource(Msaa::Off)
+        .add_plugins(TemporalAntiAliasPlugin);
+
+    app.run();
+}
+
+/// set up a simple 3D scene
+fn setup(
+    mut commands: Commands,
+    mut meshes: ResMut<Assets<Mesh>>,
+    mut materials: ResMut<Assets<StandardMaterial>>,
+    asset_server: Res<AssetServer>,
+) {
+    let icosphere_mesh = meshes.add(
+        Mesh::try_from(shape::Icosphere {
+            radius: 0.9,
+            subdivisions: 7,
+        })
+        .unwrap(),
+    );
+
+    let cube_mesh = meshes.add(Mesh::from(shape::Cube { size: 0.7 }));
+
+    let plane_mesh = meshes.add(shape::Plane::from_size(2.0).into());
+
+    let cylinder_mesh = meshes.add(
+        Mesh::try_from(shape::Cylinder {
+            radius: 0.5,
+            height: 2.0,
+            resolution: 50,
+            segments: 1,
+        })
+        .unwrap(),
+    );
+
+    // Cube #1
+    commands.spawn((
+        PbrBundle {
+            mesh: cube_mesh.clone(),
+            material: materials.add(StandardMaterial { ..default() }),
+            transform: Transform::from_xyz(0.25, 0.5, -2.0).with_rotation(Quat::from_euler(
+                EulerRot::XYZ,
+                1.4,
+                3.7,
+                21.3,
+            )),
+            ..default()
+        },
+        ExampleControls {
+            color: true,
+            specular_transmission: false,
+            diffuse_transmission: false,
+        },
+    ));
+
+    // Cube #2
+    commands.spawn((
+        PbrBundle {
+            mesh: cube_mesh,
+            material: materials.add(StandardMaterial { ..default() }),
+            transform: Transform::from_xyz(-0.75, 0.7, -2.0).with_rotation(Quat::from_euler(
+                EulerRot::XYZ,
+                0.4,
+                2.3,
+                4.7,
+            )),
+            ..default()
+        },
+        ExampleControls {
+            color: true,
+            specular_transmission: false,
+            diffuse_transmission: false,
+        },
+    ));
+
+    // Candle
+    commands.spawn((
+        PbrBundle {
+            mesh: cylinder_mesh,
+            material: materials.add(StandardMaterial {
+                base_color: Color::rgba(0.9, 0.2, 0.3, 1.0),
+                diffuse_transmission: 0.7,
+                perceptual_roughness: 0.32,
+                thickness: 0.2,
+                ..default()
+            }),
+            transform: Transform::from_xyz(-1.0, 0.0, 0.0),
+            ..default()
+        },
+        ExampleControls {
+            color: true,
+            specular_transmission: false,
+            diffuse_transmission: true,
+        },
+    ));
+
+    // Candle Flame
+    commands.spawn((
+        PbrBundle {
+            mesh: icosphere_mesh.clone(),
+            material: materials.add(StandardMaterial {
+                emissive: Color::ANTIQUE_WHITE * 20.0 + Color::ORANGE_RED * 4.0,
+                diffuse_transmission: 1.0,
+                ..default()
+            }),
+            transform: Transform::from_xyz(-1.0, 1.15, 0.0).with_scale(Vec3::new(0.1, 0.2, 0.1)),
+            ..default()
+        },
+        Flicker,
+        NotShadowCaster,
+    ));
+
+    // Glass Sphere
+    commands.spawn((
+        PbrBundle {
+            mesh: icosphere_mesh.clone(),
+            material: materials.add(StandardMaterial {
+                base_color: Color::WHITE,
+                specular_transmission: 0.9,
+                diffuse_transmission: 1.0,
+                thickness: 1.8,
+                ior: 1.5,
+                perceptual_roughness: 0.12,
+                ..default()
+            }),
+            transform: Transform::from_xyz(1.0, 0.0, 0.0),
+            ..default()
+        },
+        ExampleControls {
+            color: true,
+            specular_transmission: true,
+            diffuse_transmission: false,
+        },
+    ));
+
+    // R Sphere
+    commands.spawn((
+        PbrBundle {
+            mesh: icosphere_mesh.clone(),
+            material: materials.add(StandardMaterial {
+                base_color: Color::RED,
+                specular_transmission: 0.9,
+                diffuse_transmission: 1.0,
+                thickness: 1.8,
+                ior: 1.5,
+                perceptual_roughness: 0.12,
+                ..default()
+            }),
+            transform: Transform::from_xyz(1.0, -0.5, 2.0).with_scale(Vec3::splat(0.5)),
+            ..default()
+        },
+        ExampleControls {
+            color: true,
+            specular_transmission: true,
+            diffuse_transmission: false,
+        },
+    ));
+
+    // G Sphere
+    commands.spawn((
+        PbrBundle {
+            mesh: icosphere_mesh.clone(),
+            material: materials.add(StandardMaterial {
+                base_color: Color::GREEN,
+                specular_transmission: 0.9,
+                diffuse_transmission: 1.0,
+                thickness: 1.8,
+                ior: 1.5,
+                perceptual_roughness: 0.12,
+                ..default()
+            }),
+            transform: Transform::from_xyz(0.0, -0.5, 2.0).with_scale(Vec3::splat(0.5)),
+            ..default()
+        },
+        ExampleControls {
+            color: true,
+            specular_transmission: true,
+            diffuse_transmission: false,
+        },
+    ));
+
+    // B Sphere
+    commands.spawn((
+        PbrBundle {
+            mesh: icosphere_mesh,
+            material: materials.add(StandardMaterial {
+                base_color: Color::BLUE,
+                specular_transmission: 0.9,
+                diffuse_transmission: 1.0,
+                thickness: 1.8,
+                ior: 1.5,
+                perceptual_roughness: 0.12,
+                ..default()
+            }),
+            transform: Transform::from_xyz(-1.0, -0.5, 2.0).with_scale(Vec3::splat(0.5)),
+            ..default()
+        },
+        ExampleControls {
+            color: true,
+            specular_transmission: true,
+            diffuse_transmission: false,
+        },
+    ));
+
+    // Chessboard Plane
+    let black_material = materials.add(StandardMaterial {
+        base_color: Color::BLACK,
+        reflectance: 0.3,
+        perceptual_roughness: 0.8,
+        ..default()
+    });
+
+    let white_material = materials.add(StandardMaterial {
+        base_color: Color::WHITE,
+        reflectance: 0.3,
+        perceptual_roughness: 0.8,
+        ..default()
+    });
+
+    for x in -3..4 {
+        for z in -3..4 {
+            commands.spawn((
+                PbrBundle {
+                    mesh: plane_mesh.clone(),
+                    material: if (x + z) % 2 == 0 {
+                        black_material.clone()
+                    } else {
+                        white_material.clone()
+                    },
+                    transform: Transform::from_xyz(x as f32 * 2.0, -1.0, z as f32 * 2.0),
+                    ..default()
+                },
+                ExampleControls {
+                    color: true,
+                    specular_transmission: false,
+                    diffuse_transmission: false,
+                },
+            ));
+        }
+    }
+
+    // Paper
+    commands.spawn((
+        PbrBundle {
+            mesh: plane_mesh,
+            material: materials.add(StandardMaterial {
+                base_color: Color::WHITE,
+                diffuse_transmission: 0.6,
+                perceptual_roughness: 0.8,
+                reflectance: 1.0,
+                double_sided: true,
+                cull_mode: None,
+                ..default()
+            }),
+            transform: Transform::from_xyz(0.0, 0.5, -3.0)
+                .with_scale(Vec3::new(2.0, 1.0, 1.0))
+                .with_rotation(Quat::from_euler(EulerRot::XYZ, PI / 2.0, 0.0, 0.0)),
+            ..default()
+        },
+        TransmittedShadowReceiver,
+        ExampleControls {
+            specular_transmission: false,
+            color: false,
+            diffuse_transmission: true,
+        },
+    ));
+
+    // Candle Light
+    commands.spawn((
+        PointLightBundle {
+            transform: Transform::from_xyz(-1.0, 1.7, 0.0),
+            point_light: PointLight {
+                color: Color::ANTIQUE_WHITE * 0.8 + Color::ORANGE_RED * 0.2,
+                intensity: 1600.0,
+                radius: 0.2,
+                range: 5.0,
+                shadows_enabled: true,
+                ..default()
+            },
+            ..default()
+        },
+        Flicker,
+    ));
+
+    // Camera
+    commands.spawn((
+        Camera3dBundle {
+            camera: Camera {
+                hdr: true,
+                ..default()
+            },
+            transform: Transform::from_xyz(1.0, 1.8, 7.0).looking_at(Vec3::ZERO, Vec3::Y),
+            color_grading: ColorGrading {
+                exposure: -2.0,
+                post_saturation: 1.2,
+                ..default()
+            },
+            tonemapping: Tonemapping::TonyMcMapface,
+            ..default()
+        },
+        #[cfg(not(all(feature = "webgl2", target_arch = "wasm32")))]
+        TemporalAntiAliasBundle::default(),
+        EnvironmentMapLight {
+            diffuse_map: asset_server.load("environment_maps/pisa_diffuse_rgb9e5_zstd.ktx2"),
+            specular_map: asset_server.load("environment_maps/pisa_specular_rgb9e5_zstd.ktx2"),
+        },
+        BloomSettings::default(),
+    ));
+
+    // Controls Text
+    let text_style = TextStyle {
+        font_size: 18.0,
+        color: Color::WHITE,
+        ..Default::default()
+    };
+
+    commands.spawn((
+        TextBundle::from_section("", text_style).with_style(Style {
+            position_type: PositionType::Absolute,
+            top: Val::Px(10.0),
+            left: Val::Px(10.0),
+            ..default()
+        }),
+        ExampleDisplay,
+    ));
+}
+
+#[derive(Component)]
+struct Flicker;
+
+#[derive(Component)]
+struct ExampleControls {
+    diffuse_transmission: bool,
+    specular_transmission: bool,
+    color: bool,
+}
+
+struct ExampleState {
+    diffuse_transmission: f32,
+    specular_transmission: f32,
+    thickness: f32,
+    ior: f32,
+    perceptual_roughness: f32,
+    reflectance: f32,
+    auto_camera: bool,
+}
+
+#[derive(Component)]
+struct ExampleDisplay;
+
+impl Default for ExampleState {
+    fn default() -> Self {
+        ExampleState {
+            diffuse_transmission: 0.5,
+            specular_transmission: 0.9,
+            thickness: 1.8,
+            ior: 1.5,
+            perceptual_roughness: 0.12,
+            reflectance: 0.5,
+            auto_camera: true,
+        }
+    }
+}
+
+#[allow(clippy::too_many_arguments)]
+fn example_control_system(
+    mut commands: Commands,
+    mut materials: ResMut<Assets<StandardMaterial>>,
+    controllable: Query<(&Handle<StandardMaterial>, &ExampleControls)>,
+    mut camera: Query<
+        (
+            Entity,
+            &mut Camera,
+            &mut Camera3d,
+            &mut Transform,
+            Option<&DepthPrepass>,
+            Option<&TemporalJitter>,
+        ),
+        With<Camera3d>,
+    >,
+    mut display: Query<&mut Text, With<ExampleDisplay>>,
+    mut state: Local<ExampleState>,
+    time: Res<Time>,
+    input: Res<Input<KeyCode>>,
+) {
+    if input.pressed(KeyCode::Key2) {
+        state.diffuse_transmission = (state.diffuse_transmission + time.delta_seconds()).min(1.0);
+    } else if input.pressed(KeyCode::Key1) {
+        state.diffuse_transmission = (state.diffuse_transmission - time.delta_seconds()).max(0.0);
+    }
+
+    if input.pressed(KeyCode::W) {
+        state.specular_transmission = (state.specular_transmission + time.delta_seconds()).min(1.0);
+    } else if input.pressed(KeyCode::Q) {
+        state.specular_transmission = (state.specular_transmission - time.delta_seconds()).max(0.0);
+    }
+
+    if input.pressed(KeyCode::S) {
+        state.thickness = (state.thickness + time.delta_seconds()).min(5.0);
+    } else if input.pressed(KeyCode::A) {
+        state.thickness = (state.thickness - time.delta_seconds()).max(0.0);
+    }
+
+    if input.pressed(KeyCode::X) {
+        state.ior = (state.ior + time.delta_seconds()).min(3.0);
+    } else if input.pressed(KeyCode::Z) {
+        state.ior = (state.ior - time.delta_seconds()).max(1.0);
+    }
+
+    if input.pressed(KeyCode::I) {
+        state.reflectance = (state.reflectance + time.delta_seconds()).min(1.0);
+    } else if input.pressed(KeyCode::U) {
+        state.reflectance = (state.reflectance - time.delta_seconds()).max(0.0);
+    }
+
+    if input.pressed(KeyCode::R) {
+        state.perceptual_roughness = (state.perceptual_roughness + time.delta_seconds()).min(1.0);
+    } else if input.pressed(KeyCode::E) {
+        state.perceptual_roughness = (state.perceptual_roughness - time.delta_seconds()).max(0.0);
+    }
+
+    let randomize_colors = input.just_pressed(KeyCode::C);
+
+    for (material_handle, controls) in &controllable {
+        let material = materials.get_mut(material_handle).unwrap();
+        if controls.specular_transmission {
+            material.specular_transmission = state.specular_transmission;
+            material.thickness = state.thickness;
+            material.ior = state.ior;
+            material.perceptual_roughness = state.perceptual_roughness;
+            material.reflectance = state.reflectance;
+        }
+
+        if controls.diffuse_transmission {
+            material.diffuse_transmission = state.diffuse_transmission;
+        }
+
+        if controls.color && randomize_colors {
+            material.base_color.set_r(random());
+            material.base_color.set_g(random());
+            material.base_color.set_b(random());
+        }
+    }
+
+    let (
+        camera_entity,
+        mut camera,
+        mut camera_3d,
+        mut camera_transform,
+        depth_prepass,
+        temporal_jitter,
+    ) = camera.single_mut();
+
+    if input.just_pressed(KeyCode::H) {
+        camera.hdr = !camera.hdr;
+    }
+
+    #[cfg(not(all(feature = "webgl2", target_arch = "wasm32")))]
+    if input.just_pressed(KeyCode::D) {
+        if depth_prepass.is_none() {
+            commands.entity(camera_entity).insert(DepthPrepass);
+        } else {
+            commands.entity(camera_entity).remove::<DepthPrepass>();
+        }
+    }
+
+    #[cfg(not(all(feature = "webgl2", target_arch = "wasm32")))]
+    if input.just_pressed(KeyCode::T) {
+        if temporal_jitter.is_none() {
+            commands.entity(camera_entity).insert((
+                TemporalJitter::default(),
+                TemporalAntiAliasSettings::default(),
+            ));
+        } else {
+            commands
+                .entity(camera_entity)
+                .remove::<(TemporalJitter, TemporalAntiAliasSettings)>();
+        }
+    }
+
+    if input.just_pressed(KeyCode::O) && camera_3d.screen_space_specular_transmission_steps > 0 {
+        camera_3d.screen_space_specular_transmission_steps -= 1;
+    }
+
+    if input.just_pressed(KeyCode::P) && camera_3d.screen_space_specular_transmission_steps < 4 {
+        camera_3d.screen_space_specular_transmission_steps += 1;
+    }
+
+    if input.just_pressed(KeyCode::J) {
+        camera_3d.screen_space_specular_transmission_quality = ScreenSpaceTransmissionQuality::Low;
+    }
+
+    if input.just_pressed(KeyCode::K) {
+        camera_3d.screen_space_specular_transmission_quality =
+            ScreenSpaceTransmissionQuality::Medium;
+    }
+
+    if input.just_pressed(KeyCode::L) {
+        camera_3d.screen_space_specular_transmission_quality = ScreenSpaceTransmissionQuality::High;
+    }
+
+    if input.just_pressed(KeyCode::Semicolon) {
+        camera_3d.screen_space_specular_transmission_quality =
+            ScreenSpaceTransmissionQuality::Ultra;
+    }
+
+    let rotation = if input.pressed(KeyCode::Right) {
+        state.auto_camera = false;
+        time.delta_seconds()
+    } else if input.pressed(KeyCode::Left) {
+        state.auto_camera = false;
+        -time.delta_seconds()
+    } else if state.auto_camera {
+        time.delta_seconds() * 0.25
+    } else {
+        0.0
+    };
+
+    let distance_change =
+        if input.pressed(KeyCode::Down) && camera_transform.translation.length() < 25.0 {
+            time.delta_seconds()
+        } else if input.pressed(KeyCode::Up) && camera_transform.translation.length() > 2.0 {
+            -time.delta_seconds()
+        } else {
+            0.0
+        };
+
+    camera_transform.translation *= distance_change.exp();
+
+    camera_transform.rotate_around(
+        Vec3::ZERO,
+        Quat::from_euler(EulerRot::XYZ, 0.0, rotation, 0.0),
+    );
+
+    let mut display = display.single_mut();
+    display.sections[0].value = format!(
+        concat!(
+            " J / K / L / ;  Screen Space Specular Transmissive Quality: {:?}\n",
+            "         O / P  Screen Space Specular Transmissive Steps: {}\n",
+            "         1 / 2  Diffuse Transmission: {:.2}\n",
+            "         Q / W  Specular Transmission: {:.2}\n",
+            "         A / S  Thickness: {:.2}\n",
+            "         Z / X  IOR: {:.2}\n",
+            "         E / R  Perceptual Roughness: {:.2}\n",
+            "         U / I  Reflectance: {:.2}\n",
+            "    Arrow Keys  Control Camera\n",
+            "             C  Randomize Colors\n",
+            "             H  HDR + Bloom: {}\n",
+            "             D  Depth Prepass: {}\n",
+            "             T  TAA: {}\n",
+        ),
+        camera_3d.screen_space_specular_transmission_quality,
+        camera_3d.screen_space_specular_transmission_steps,
+        state.diffuse_transmission,
+        state.specular_transmission,
+        state.thickness,
+        state.ior,
+        state.perceptual_roughness,
+        state.reflectance,
+        if camera.hdr { "ON " } else { "OFF" },
+        if cfg!(any(not(feature = "webgl2"), not(target_arch = "wasm32"))) {
+            if depth_prepass.is_some() {
+                "ON "
+            } else {
+                "OFF"
+            }
+        } else {
+            "N/A (WebGL)"
+        },
+        if cfg!(any(not(feature = "webgl2"), not(target_arch = "wasm32"))) {
+            if temporal_jitter.is_some() {
+                if depth_prepass.is_some() {
+                    "ON "
+                } else {
+                    "N/A (Needs Depth Prepass)"
+                }
+            } else {
+                "OFF"
+            }
+        } else {
+            "N/A (WebGL)"
+        },
+    );
+}
+
+fn flicker_system(
+    mut flame: Query<&mut Transform, (With<Flicker>, With<Handle<Mesh>>)>,
+    mut light: Query<(&mut PointLight, &mut Transform), (With<Flicker>, Without<Handle<Mesh>>)>,
+    time: Res<Time>,
+) {
+    let s = time.elapsed_seconds();
+    let a = (s * 6.0).cos() * 0.0125 + (s * 4.0).cos() * 0.025;
+    let b = (s * 5.0).cos() * 0.0125 + (s * 3.0).cos() * 0.025;
+    let c = (s * 7.0).cos() * 0.0125 + (s * 2.0).cos() * 0.025;
+    let (mut light, mut light_transform) = light.single_mut();
+    let mut flame_transform = flame.single_mut();
+    light.intensity = 1600.0 + 3000.0 * (a + b + c);
+    flame_transform.translation = Vec3::new(-1.0, 1.23, 0.0);
+    flame_transform.look_at(Vec3::new(-1.0 - c, 1.7 - b, 0.0 - a), Vec3::X);
+    flame_transform.rotate(Quat::from_euler(EulerRot::XYZ, 0.0, 0.0, PI / 2.0));
+    light_transform.translation = Vec3::new(-1.0 - c, 1.7, 0.0 - a);
+    flame_transform.translation = Vec3::new(-1.0 - c, 1.23, 0.0 - a);
+}

examples/README.md

@@ -142,6 +142,7 @@ Example | Description
 [Spotlight](../examples/3d/spotlight.rs) | Illustrates spot lights
 [Texture](../examples/3d/texture.rs) | Shows configuration of texture materials
 [Tonemapping](../examples/3d/tonemapping.rs) | Compares tonemapping options
+[Transmission](../examples/3d/transmission.rs) | Showcases light transmission in the PBR material
 [Transparency in 3D](../examples/3d/transparency_3d.rs) | Demonstrates transparency in 3d
 [Two Passes](../examples/3d/two_passes.rs) | Renders two 3d passes to the same window from different perspectives
 [Update glTF Scene](../examples/3d/update_gltf_scene.rs) | Update a scene from a glTF file, either by spawning the scene as a child of another entity, or by accessing the entities of the scene