Split Transmissive3d into a separate pass

crates/bevy_core_pipeline/src/core_3d/main_transmissive_pass_3d_node.rs

@@ -0,0 +1,106 @@
+use super::ViewTransmissionTexture;
+use crate::core_3d::Transmissive3d;
+use bevy_ecs::prelude::*;
+use bevy_render::{
+    camera::ExtractedCamera,
+    render_graph::{Node, NodeRunError, RenderGraphContext},
+    render_phase::RenderPhase,
+    render_resource::{
+        Extent3d, LoadOp, Operations, RenderPassDepthStencilAttachment, RenderPassDescriptor,
+    },
+    renderer::RenderContext,
+    view::{ExtractedView, ViewDepthTexture, ViewTarget},
+};
+#[cfg(feature = "trace")]
+use bevy_utils::tracing::info_span;
+
+/// A [`Node`] that runs the [`Transmissive3d`] [`RenderPhase`].
+pub struct MainTransmissivePass3dNode {
+    query: QueryState<
+        (
+            &'static ExtractedCamera,
+            &'static RenderPhase<Transmissive3d>,
+            &'static ViewTarget,
+            &'static ViewTransmissionTexture,
+            &'static ViewDepthTexture,
+        ),
+        With<ExtractedView>,
+    >,
+}
+
+impl FromWorld for MainTransmissivePass3dNode {
+    fn from_world(world: &mut World) -> Self {
+        Self {
+            query: world.query_filtered(),
+        }
+    }
+}
+
+impl Node for MainTransmissivePass3dNode {
+    fn update(&mut self, world: &mut World) {
+        self.query.update_archetypes(world);
+    }
+
+    fn run(
+        &self,
+        graph: &mut RenderGraphContext,
+        render_context: &mut RenderContext,
+        world: &World,
+    ) -> Result<(), NodeRunError> {
+        let view_entity = graph.view_entity();
+        let Ok((
+            camera,
+            transmissive_phase,
+            target,
+            transmission,
+            depth,
+        )) = self.query.get_manual(world, view_entity) else {
+            // No window
+            return Ok(());
+        };
+
+        let physical_target_size = camera.physical_target_size.unwrap();
+        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,
+            },
+        );
+
+        if !transmissive_phase.items.is_empty() {
+            // 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();
+
+            let mut render_pass = render_context.begin_tracked_render_pass(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,
+                }),
+            });
+
+            if let Some(viewport) = camera.viewport.as_ref() {
+                render_pass.set_camera_viewport(viewport);
+            }
+
+            transmissive_phase.render(&mut render_pass, world, view_entity);
+        }
+
+        Ok(())
+    }
+}

crates/bevy_core_pipeline/src/core_3d/main_transparent_pass_3d_node.rs

@@ -1,13 +1,10 @@
-use super::ViewTransmissionTexture;
 use crate::core_3d::Transparent3d;
 use bevy_ecs::prelude::*;
 use bevy_render::{
     camera::ExtractedCamera,
     render_graph::{Node, NodeRunError, RenderGraphContext},
     render_phase::RenderPhase,
-    render_resource::{
+    render_resource::{LoadOp, Operations, RenderPassDepthStencilAttachment, RenderPassDescriptor},
-        Extent3d, LoadOp, Operations, RenderPassDepthStencilAttachment, RenderPassDescriptor,
-    },
     renderer::RenderContext,
     view::{ExtractedView, ViewDepthTexture, ViewTarget},
 };
@@ -21,7 +18,6 @@ pub struct MainTransparentPass3dNode {
             &'static ExtractedCamera,
             &'static RenderPhase<Transparent3d>,
             &'static ViewTarget,
-            &'static ViewTransmissionTexture,
             &'static ViewDepthTexture,
         ),
         With<ExtractedView>,
@@ -52,24 +48,12 @@ impl Node for MainTransparentPass3dNode {
             camera,
             transparent_phase,
             target,
-            transmission,
             depth,
         )) = self.query.get_manual(world, view_entity) else {
             // No window
             return Ok(());
         };
 
-        let physical_target_size = camera.physical_target_size.unwrap();
-        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,
-            },
-        );
-
         if !transparent_phase.items.is_empty() {
             // Run the transparent pass, sorted back-to-front
             // NOTE: Scoped to drop the mutable borrow of render_context

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 {
@@ -12,6 +13,7 @@ pub mod graph {
         pub const PREPASS: &str = "prepass";
         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";
@@ -53,6 +55,7 @@ use bevy_render::{
 use bevy_utils::{FloatOrd, HashMap};
 
 use crate::{
+    core_3d::main_transmissive_pass_3d_node::MainTransmissivePass3dNode,
     prepass::{node::PrepassNode, DepthPrepass},
     skybox::SkyboxPlugin,
     tonemapping::TonemappingNode,
@@ -76,6 +79,7 @@ impl Plugin for Core3dPlugin {
         render_app
             .init_resource::<DrawFunctions<Opaque3d>>()
             .init_resource::<DrawFunctions<AlphaMask3d>>()
+            .init_resource::<DrawFunctions<Transmissive3d>>()
             .init_resource::<DrawFunctions<Transparent3d>>()
             .add_systems(ExtractSchedule, extract_core_3d_camera_phases)
             .add_systems(
@@ -89,6 +93,7 @@ impl Plugin for Core3dPlugin {
                         .after(bevy_render::view::prepare_windows),
                     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),
                 ),
             );
@@ -99,6 +104,7 @@ impl Plugin for Core3dPlugin {
             .add_render_graph_node::<PrepassNode>(CORE_3D, PREPASS)
             .add_render_graph_node::<EmptyNode>(CORE_3D, START_MAIN_PASS)
             .add_render_graph_node::<MainOpaquePass3dNode>(CORE_3D, MAIN_OPAQUE_PASS)
+            .add_render_graph_node::<MainTransmissivePass3dNode>(CORE_3D, MAIN_TRANSMISSIVE_PASS)
             .add_render_graph_node::<MainTransparentPass3dNode>(CORE_3D, MAIN_TRANSPARENT_PASS)
             .add_render_graph_node::<EmptyNode>(CORE_3D, END_MAIN_PASS)
             .add_render_graph_node::<TonemappingNode>(CORE_3D, TONEMAPPING)
@@ -110,6 +116,7 @@ impl Plugin for Core3dPlugin {
                     PREPASS,
                     START_MAIN_PASS,
                     MAIN_OPAQUE_PASS,
+                    MAIN_TRANSMISSIVE_PASS,
                     MAIN_TRANSPARENT_PASS,
                     END_MAIN_PASS,
                     TONEMAPPING,
@@ -200,6 +207,45 @@ impl CachedRenderPipelinePhaseItem for AlphaMask3d {
     }
 }
 
+pub struct Transmissive3d {
+    pub distance: f32,
+    pub pipeline: CachedRenderPipelineId,
+    pub entity: Entity,
+    pub draw_function: DrawFunctionId,
+}
+
+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;
+
+    #[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);
+    }
+}
+
+impl CachedRenderPipelinePhaseItem for Transmissive3d {
+    #[inline]
+    fn cached_pipeline(&self) -> CachedRenderPipelineId {
+        self.pipeline
+    }
+}
+
 pub struct Transparent3d {
     pub distance: f32,
     pub pipeline: CachedRenderPipelineId,
@@ -248,6 +294,7 @@ 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(),
             ));
         }
@@ -264,6 +311,7 @@ pub fn prepare_core_3d_depth_textures(
         (
             With<RenderPhase<Opaque3d>>,
             With<RenderPhase<AlphaMask3d>>,
+            With<RenderPhase<Transmissive3d>>,
             With<RenderPhase<Transparent3d>>,
         ),
     >,
@@ -330,6 +378,7 @@ pub fn prepare_core_3d_transmission_textures(
         (
             With<RenderPhase<Opaque3d>>,
             With<RenderPhase<AlphaMask3d>>,
+            With<RenderPhase<Transmissive3d>>,
             With<RenderPhase<Transparent3d>>,
         ),
     >,

crates/bevy_pbr/src/material.rs

@@ -6,7 +6,7 @@ use crate::{
 use bevy_app::{App, Plugin};
 use bevy_asset::{AddAsset, AssetEvent, AssetServer, Assets, Handle};
 use bevy_core_pipeline::{
-    core_3d::{AlphaMask3d, Opaque3d, Transparent3d},
+    core_3d::{AlphaMask3d, Opaque3d, Transmissive3d, Transparent3d},
     prepass::NormalPrepass,
     tonemapping::{DebandDither, Tonemapping},
 };
@@ -133,6 +133,13 @@ pub trait Material: AsBindGroup + Send + Sync + Clone + TypeUuid + Sized + 'stat
         0.0
     }
 
+    #[inline]
+    /// Returns whether or not the material has light transmission properties. Transmissive materials use the color
+    /// output from the [`Opaque3d`] pass as an input and therefore must run in a separate [`Transmissive3d`] pass.
+    fn transmissive(&self) -> bool {
+        false
+    }
+
     /// Returns this material's prepass vertex shader. If [`ShaderRef::Default`] is returned, the default prepass vertex shader
     /// will be used.
     fn prepass_vertex_shader() -> ShaderRef {
@@ -193,6 +200,7 @@ 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>>()
@@ -366,6 +374,7 @@ impl<P: PhaseItem, M: Material, const I: usize> RenderCommand<P> for SetMaterial
 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>>>,
@@ -384,6 +393,7 @@ pub fn queue_material_meshes<M: Material>(
         Option<&NormalPrepass>,
         &mut RenderPhase<Opaque3d>,
         &mut RenderPhase<AlphaMask3d>,
+        &mut RenderPhase<Transmissive3d>,
         &mut RenderPhase<Transparent3d>,
     )>,
 ) where
@@ -398,11 +408,13 @@ pub fn queue_material_meshes<M: Material>(
         normal_prepass,
         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())
@@ -491,6 +503,14 @@ pub fn queue_material_meshes<M: Material>(
                         + material.properties.depth_bias;
                     match material.properties.alpha_mode {
                         AlphaMode::Opaque => {
+                            if material.properties.transmissive {
+                                transmissive_phase.add(Transmissive3d {
+                                    entity: *visible_entity,
+                                    draw_function: draw_transmissive_pbr,
+                                    pipeline: pipeline_id,
+                                    distance,
+                                });
+                            } else {
                                 opaque_phase.add(Opaque3d {
                                     entity: *visible_entity,
                                     draw_function: draw_opaque_pbr,
@@ -498,6 +518,7 @@ pub fn queue_material_meshes<M: Material>(
                                     distance,
                                 });
                             }
+                        }
                         AlphaMode::Mask(_) => {
                             alpha_mask_phase.add(AlphaMask3d {
                                 entity: *visible_entity,
@@ -532,6 +553,9 @@ 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 or not the material has light transmission properties. Transmissive materials use the color
+    /// output from the [`Opaque3d`] pass as an input and therefore must run in a separate [`Transmissive3d`] pass.
+    pub transmissive: bool,
 }
 
 /// Data prepared for a [`Material`] instance.
@@ -685,6 +709,7 @@ fn prepare_material<M: Material>(
         properties: MaterialProperties {
             alpha_mode: material.alpha_mode(),
             depth_bias: material.depth_bias(),
+            transmissive: material.transmissive(),
         },
     })
 }

crates/bevy_pbr/src/pbr_material.rs

@@ -530,4 +530,9 @@ impl Material for StandardMaterial {
     fn depth_bias(&self) -> f32 {
         self.depth_bias
     }
+
+    #[inline]
+    fn transmissive(&self) -> bool {
+        self.transmission > 0.0
+    }
 }

examples/3d/transmission.rs

@@ -74,7 +74,6 @@ fn setup(
                 thickness: 1.0,
                 ior: 1.5,
                 perceptual_roughness: 0.12,
-                alpha_mode: AlphaMode::Blend,
                 ..default()
             }),
             transform: Transform::from_xyz(1.0, 0.0, 0.0),