Make PCSS experimental (#16382)

# Objective

PCSS still has some fundamental issues (#16155). We should resolve them
before "releasing" the feature.

## Solution

1. Rename the already-optional `pbr_pcss` cargo feature to
`experimental_pbr_pcss` to better communicate its state to developers.
2. Adjust the description of the `experimental_pbr_pcss` cargo feature
to better communicate its state to developers.
3. Gate PCSS-related light component fields behind that cargo feature,
to prevent surfacing them to developers by default.

Cargo.toml

@@ -405,7 +405,7 @@ pbr_multi_layer_material_textures = [
 pbr_anisotropy_texture = ["bevy_internal/pbr_anisotropy_texture"]
 
 # Enable support for PCSS, at the risk of blowing past the global, per-shader sampler limit on older/lower-end GPUs
-pbr_pcss = ["bevy_internal/pbr_pcss"]
+experimental_pbr_pcss = ["bevy_internal/experimental_pbr_pcss"]
 
 # Enable some limitations to be able to use WebGL2. 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"]
@@ -3792,7 +3792,7 @@ wasm = true
 name = "pcss"
 path = "examples/3d/pcss.rs"
 doc-scrape-examples = true
-required-features = ["pbr_pcss"]
+required-features = ["experimental_pbr_pcss"]
 
 [package.metadata.example.pcss]
 name = "Percentage-closer soft shadows"

crates/bevy_internal/Cargo.toml

@@ -135,7 +135,7 @@ pbr_anisotropy_texture = [
 ]
 
 # Percentage-closer soft shadows
-pbr_pcss = ["bevy_pbr?/pbr_pcss"]
+experimental_pbr_pcss = ["bevy_pbr?/experimental_pbr_pcss"]
 
 # Optimise for WebGL2
 webgl = [

crates/bevy_pbr/Cargo.toml

@@ -14,7 +14,7 @@ webgpu = []
 pbr_transmission_textures = []
 pbr_multi_layer_material_textures = []
 pbr_anisotropy_texture = []
-pbr_pcss = []
+experimental_pbr_pcss = []
 shader_format_glsl = ["bevy_render/shader_format_glsl"]
 trace = ["bevy_render/trace"]
 ios_simulator = ["bevy_render/ios_simulator"]

crates/bevy_pbr/src/light/directional_light.rs

@@ -95,6 +95,7 @@ pub struct DirectionalLight {
     ///
     /// Note that soft shadows are significantly more expensive to render than
     /// hard shadows.
+    #[cfg(feature = "experimental_pbr_pcss")]
     pub soft_shadow_size: Option<f32>,
 
     /// A value that adjusts the tradeoff between self-shadowing artifacts and
@@ -120,9 +121,10 @@ impl Default for DirectionalLight {
             color: Color::WHITE,
             illuminance: light_consts::lux::AMBIENT_DAYLIGHT,
             shadows_enabled: false,
-            soft_shadow_size: None,
             shadow_depth_bias: Self::DEFAULT_SHADOW_DEPTH_BIAS,
             shadow_normal_bias: Self::DEFAULT_SHADOW_NORMAL_BIAS,
+            #[cfg(feature = "experimental_pbr_pcss")]
+            soft_shadow_size: None,
         }
     }
 }

crates/bevy_pbr/src/light/point_light.rs

@@ -61,6 +61,7 @@ pub struct PointLight {
     ///
     /// Note that soft shadows are significantly more expensive to render than
     /// hard shadows.
+    #[cfg(feature = "experimental_pbr_pcss")]
     pub soft_shadows_enabled: bool,
 
     /// A bias used when sampling shadow maps to avoid "shadow-acne", or false shadow occlusions
@@ -95,10 +96,11 @@ impl Default for PointLight {
             range: 20.0,
             radius: 0.0,
             shadows_enabled: false,
-            soft_shadows_enabled: false,
             shadow_depth_bias: Self::DEFAULT_SHADOW_DEPTH_BIAS,
             shadow_normal_bias: Self::DEFAULT_SHADOW_NORMAL_BIAS,
             shadow_map_near_z: Self::DEFAULT_SHADOW_MAP_NEAR_Z,
+            #[cfg(feature = "experimental_pbr_pcss")]
+            soft_shadows_enabled: false,
         }
     }
 }

crates/bevy_pbr/src/light/spot_light.rs

@@ -57,6 +57,7 @@ pub struct SpotLight {
     ///
     /// Note that soft shadows are significantly more expensive to render than
     /// hard shadows.
+    #[cfg(feature = "experimental_pbr_pcss")]
     pub soft_shadows_enabled: bool,
 
     /// A value that adjusts the tradeoff between self-shadowing artifacts and
@@ -115,12 +116,13 @@ impl Default for SpotLight {
             range: 20.0,
             radius: 0.0,
             shadows_enabled: false,
-            soft_shadows_enabled: false,
             shadow_depth_bias: Self::DEFAULT_SHADOW_DEPTH_BIAS,
             shadow_normal_bias: Self::DEFAULT_SHADOW_NORMAL_BIAS,
             shadow_map_near_z: Self::DEFAULT_SHADOW_MAP_NEAR_Z,
             inner_angle: 0.0,
             outer_angle: core::f32::consts::FRAC_PI_4,
+            #[cfg(feature = "experimental_pbr_pcss")]
+            soft_shadows_enabled: false,
         }
     }
 }

crates/bevy_pbr/src/render/light.rs

@@ -43,12 +43,12 @@ pub struct ExtractedPointLight {
     pub radius: f32,
     pub transform: GlobalTransform,
     pub shadows_enabled: bool,
-    pub soft_shadows_enabled: bool,
     pub shadow_depth_bias: f32,
     pub shadow_normal_bias: f32,
     pub shadow_map_near_z: f32,
     pub spot_light_angles: Option<(f32, f32)>,
     pub volumetric: bool,
+    pub soft_shadows_enabled: bool,
 }
 
 #[derive(Component, Debug)]
@@ -58,13 +58,13 @@ pub struct ExtractedDirectionalLight {
     pub transform: GlobalTransform,
     pub shadows_enabled: bool,
     pub volumetric: bool,
-    pub soft_shadow_size: Option<f32>,
     pub shadow_depth_bias: f32,
     pub shadow_normal_bias: f32,
     pub cascade_shadow_config: CascadeShadowConfig,
     pub cascades: EntityHashMap<Vec<Cascade>>,
     pub frusta: EntityHashMap<Vec<Frustum>>,
     pub render_layers: RenderLayers,
+    pub soft_shadow_size: Option<f32>,
 }
 
 // NOTE: These must match the bit flags in bevy_pbr/src/render/mesh_view_types.wgsl!
@@ -149,10 +149,10 @@ pub const MAX_CASCADES_PER_LIGHT: usize = 1;
 #[derive(Resource, Clone)]
 pub struct ShadowSamplers {
     pub point_light_comparison_sampler: Sampler,
-    #[cfg(feature = "pbr_pcss")]
+    #[cfg(feature = "experimental_pbr_pcss")]
     pub point_light_linear_sampler: Sampler,
     pub directional_light_comparison_sampler: Sampler,
-    #[cfg(feature = "pbr_pcss")]
+    #[cfg(feature = "experimental_pbr_pcss")]
     pub directional_light_linear_sampler: Sampler,
 }
 
@@ -176,7 +176,7 @@ impl FromWorld for ShadowSamplers {
                 compare: Some(CompareFunction::GreaterEqual),
                 ..base_sampler_descriptor
             }),
-            #[cfg(feature = "pbr_pcss")]
+            #[cfg(feature = "experimental_pbr_pcss")]
             point_light_linear_sampler: render_device.create_sampler(&base_sampler_descriptor),
             directional_light_comparison_sampler: render_device.create_sampler(
                 &SamplerDescriptor {
@@ -184,7 +184,7 @@ impl FromWorld for ShadowSamplers {
                     ..base_sampler_descriptor
                 },
             ),
-            #[cfg(feature = "pbr_pcss")]
+            #[cfg(feature = "experimental_pbr_pcss")]
             directional_light_linear_sampler: render_device
                 .create_sampler(&base_sampler_descriptor),
         }
@@ -293,7 +293,6 @@ pub fn extract_lights(
             radius: point_light.radius,
             transform: *transform,
             shadows_enabled: point_light.shadows_enabled,
-            soft_shadows_enabled: point_light.soft_shadows_enabled,
             shadow_depth_bias: point_light.shadow_depth_bias,
             // The factor of SQRT_2 is for the worst-case diagonal offset
             shadow_normal_bias: point_light.shadow_normal_bias
@@ -302,6 +301,10 @@ pub fn extract_lights(
             shadow_map_near_z: point_light.shadow_map_near_z,
             spot_light_angles: None,
             volumetric: volumetric_light.is_some(),
+            #[cfg(feature = "experimental_pbr_pcss")]
+            soft_shadows_enabled: point_light.soft_shadows_enabled,
+            #[cfg(not(feature = "experimental_pbr_pcss"))]
+            soft_shadows_enabled: false,
         };
         point_lights_values.push((
             render_entity,
@@ -352,7 +355,6 @@ pub fn extract_lights(
                         radius: spot_light.radius,
                         transform: *transform,
                         shadows_enabled: spot_light.shadows_enabled,
-                        soft_shadows_enabled: spot_light.soft_shadows_enabled,
                         shadow_depth_bias: spot_light.shadow_depth_bias,
                         // The factor of SQRT_2 is for the worst-case diagonal offset
                         shadow_normal_bias: spot_light.shadow_normal_bias
@@ -361,6 +363,10 @@ pub fn extract_lights(
                         shadow_map_near_z: spot_light.shadow_map_near_z,
                         spot_light_angles: Some((spot_light.inner_angle, spot_light.outer_angle)),
                         volumetric: volumetric_light.is_some(),
+                        #[cfg(feature = "experimental_pbr_pcss")]
+                        soft_shadows_enabled: spot_light.soft_shadows_enabled,
+                        #[cfg(not(feature = "experimental_pbr_pcss"))]
+                        soft_shadows_enabled: false,
                     },
                     render_visible_entities,
                     *frustum,
@@ -432,7 +438,10 @@ pub fn extract_lights(
                     illuminance: directional_light.illuminance,
                     transform: *transform,
                     volumetric: volumetric_light.is_some(),
+                    #[cfg(feature = "experimental_pbr_pcss")]
                     soft_shadow_size: directional_light.soft_shadow_size,
+                    #[cfg(not(feature = "experimental_pbr_pcss"))]
+                    soft_shadow_size: None,
                     shadows_enabled: directional_light.shadows_enabled,
                     shadow_depth_bias: directional_light.shadow_depth_bias,
                     // The factor of SQRT_2 is for the worst-case diagonal offset
@@ -914,17 +923,17 @@ pub fn prepare_lights(
                 .extend(1.0 / (light.range * light.range)),
             position_radius: light.transform.translation().extend(light.radius),
             flags: flags.bits(),
-            soft_shadow_size: if light.soft_shadows_enabled {
-                light.radius
-            } else {
-                0.0
-            },
             shadow_depth_bias: light.shadow_depth_bias,
             shadow_normal_bias: light.shadow_normal_bias,
             shadow_map_near_z: light.shadow_map_near_z,
             spot_light_tan_angle,
             pad_a: 0.0,
             pad_b: 0.0,
+            soft_shadow_size: if light.soft_shadows_enabled {
+                light.radius
+            } else {
+                0.0
+            },
         });
         global_light_meta.entity_to_index.insert(entity, index);
     }

crates/bevy_pbr/src/render/mesh.rs

@@ -1859,7 +1859,7 @@ impl SpecializedMeshPipeline for MeshPipeline {
         #[cfg(all(feature = "webgl", target_arch = "wasm32", not(feature = "webgpu")))]
         shader_defs.push("WEBGL2".into());
 
-        #[cfg(feature = "pbr_pcss")]
+        #[cfg(feature = "experimental_pbr_pcss")]
         shader_defs.push("PCSS_SAMPLERS_AVAILABLE".into());
 
         if key.contains(MeshPipelineKey::TONEMAP_IN_SHADER) {

crates/bevy_pbr/src/render/mesh_view_bindings.rs

@@ -228,7 +228,7 @@ fn layout_entries(
             // Point Shadow Texture Array Comparison Sampler
             (3, sampler(SamplerBindingType::Comparison)),
             // Point Shadow Texture Array Linear Sampler
-            #[cfg(feature = "pbr_pcss")]
+            #[cfg(feature = "experimental_pbr_pcss")]
             (4, sampler(SamplerBindingType::Filtering)),
             // Directional Shadow Texture Array
             (
@@ -245,7 +245,7 @@ fn layout_entries(
             // Directional Shadow Texture Array Comparison Sampler
             (6, sampler(SamplerBindingType::Comparison)),
             // Directional Shadow Texture Array Linear Sampler
-            #[cfg(feature = "pbr_pcss")]
+            #[cfg(feature = "experimental_pbr_pcss")]
             (7, sampler(SamplerBindingType::Filtering)),
             // PointLights
             (
@@ -580,11 +580,11 @@ pub fn prepare_mesh_view_bind_groups(
                 (1, light_binding.clone()),
                 (2, &shadow_bindings.point_light_depth_texture_view),
                 (3, &shadow_samplers.point_light_comparison_sampler),
-                #[cfg(feature = "pbr_pcss")]
+                #[cfg(feature = "experimental_pbr_pcss")]
                 (4, &shadow_samplers.point_light_linear_sampler),
                 (5, &shadow_bindings.directional_light_depth_texture_view),
                 (6, &shadow_samplers.directional_light_comparison_sampler),
-                #[cfg(feature = "pbr_pcss")]
+                #[cfg(feature = "experimental_pbr_pcss")]
                 (7, &shadow_samplers.directional_light_linear_sampler),
                 (8, clusterable_objects_binding.clone()),
                 (

docs/cargo_features.md

@@ -67,6 +67,7 @@ The default feature set enables most of the expected features of a game engine,
 |detailed_trace|Enable detailed trace event logging. These trace events are expensive even when off, thus they require compile time opt-in|
 |dynamic_linking|Force dynamic linking, which improves iterative compile times|
 |embedded_watcher|Enables watching in memory asset providers for Bevy Asset hot-reloading|
+|experimental_pbr_pcss|Enable support for PCSS, at the risk of blowing past the global, per-shader sampler limit on older/lower-end GPUs|
 |exr|EXR image format support|
 |ff|Farbfeld image format support|
 |file_watcher|Enables watching the filesystem for Bevy Asset hot-reloading|
@@ -83,7 +84,6 @@ The default feature set enables most of the expected features of a game engine,
 |mp3|MP3 audio format support|
 |pbr_anisotropy_texture|Enable support for anisotropy texture in the `StandardMaterial`, at the risk of blowing past the global, per-shader texture limit on older/lower-end GPUs|
 |pbr_multi_layer_material_textures|Enable support for multi-layer material textures in the `StandardMaterial`, at the risk of blowing past the global, per-shader texture limit on older/lower-end GPUs|
-|pbr_pcss|Enable support for PCSS, at the risk of blowing past the global, per-shader sampler limit on older/lower-end GPUs|
 |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|
 |qoi|QOI image format support|