Gate LTC LUTs behind a feature and merge them to a texture array (#24065)

# Objective

Alternative to #24004.

https://github.com/bevyengine/bevy/pull/23288 adds ltc luts for rect
light support which implicitly requires `bevy_image/ktx2` and
`bevy_image/zstd` otherwise loading ltc luts will panic.

We either accept to always enable area light supoort (#24004), or add a
feature to opt out it (this PR).

## Solution

Gate ltc luts behind a feature and merge them to a texture array.

## Testing

`rect_light` example works.

---------

Co-authored-by: Kevin Chen <chen.kevin.f@gmail.com>

.github/workflows/example-run.yml

@@ -52,7 +52,7 @@ jobs:
             example_name=`basename $example .ron`
             echo -n $example_name > last_example_run
             echo "running $example_name - "`date`
-            time TRACE_CHROME=trace-$example_name.json CI_TESTING_CONFIG=$example cargo run --example $example_name --features "bevy_ci_testing,trace,trace_chrome,bevy_ui_debug"
+            time TRACE_CHROME=trace-$example_name.json CI_TESTING_CONFIG=$example cargo run --example $example_name --features "bevy_ci_testing,trace,trace_chrome,bevy_ui_debug,area_light_luts"
             sleep 10
             if [ `find ./ -maxdepth 1 -name 'screenshot-*.png' -print -quit` ]; then
               mkdir screenshots-$example_name
@@ -132,7 +132,7 @@ jobs:
             example_name=`basename $example .ron`
             echo -n $example_name > last_example_run
             echo "running $example_name - "`date`
-            time TRACE_CHROME=trace-$example_name.json CI_TESTING_CONFIG=$example xvfb-run cargo run --example $example_name --features "bevy_ci_testing,trace,trace_chrome,bevy_ui_debug"
+            time TRACE_CHROME=trace-$example_name.json CI_TESTING_CONFIG=$example xvfb-run cargo run --example $example_name --features "bevy_ci_testing,trace,trace_chrome,bevy_ui_debug,area_light_luts"
             sleep 10
             if [ `find ./ -maxdepth 1 -name 'screenshot-*.png' -print -quit` ]; then
               mkdir screenshots-$example_name
@@ -202,7 +202,7 @@ jobs:
             example_name=`basename $example .ron`
             echo -n $example_name > last_example_run
             echo "running $example_name - "`date`
-            time WGPU_BACKEND=dx12 TRACE_CHROME=trace-$example_name.json CI_TESTING_CONFIG=$example cargo run --example $example_name --features "statically-linked-dxc,bevy_ci_testing,trace,trace_chrome,bevy_ui_debug"
+            time WGPU_BACKEND=dx12 TRACE_CHROME=trace-$example_name.json CI_TESTING_CONFIG=$example cargo run --example $example_name --features "statically-linked-dxc,bevy_ci_testing,trace,trace_chrome,bevy_ui_debug,area_light_luts"
             sleep 10
             if [ `find ./ -maxdepth 1 -name 'screenshot-*.png' -print -quit` ]; then
               mkdir screenshots-$example_name

Cargo.toml

@@ -574,6 +574,9 @@ bluenoise_texture = ["bevy_internal/bluenoise_texture"]
 # Include a preintegrated BRDF Look Up Table for more accurate specular shading.
 dfg_lut = ["bevy_internal/dfg_lut"]
 
+# Include Look Up Tables that are required for area lights.
+area_light_luts = ["bevy_internal/area_light_luts"]
+
 # NVIDIA Deep Learning Super Sampling
 dlss = ["bevy_internal/dlss"]
 
@@ -1190,7 +1193,7 @@ wasm = true
 name = "rect_light"
 path = "examples/3d/rect_light.rs"
 doc-scrape-examples = true
-required-features = ["free_camera"]
+required-features = ["free_camera", "area_light_luts"]
 
 [package.metadata.example.rect_light]
 name = "Rectangular Area Light"
@@ -5192,6 +5195,7 @@ hidden = true
 name = "testbed_3d"
 path = "examples/testbed/3d.rs"
 doc-scrape-examples = true
+required-features = ["area_light_luts"]
 
 [package.metadata.example.testbed_3d]
 hidden = true

_release-content/release-notes/area_lights.md

@@ -12,4 +12,6 @@ The implementation uses [Linearly Transformed Cosines](https://eheitzresearch.wo
 
 Rectangular lights currently don't cast shadows or have support for anisotropic materials.
 
+You need to enable the `area_light_luts` cargo feature to use it.
+
 Check out [the new example](https://github.com/bevyengine/bevy/tree/latest/examples/3d/rect_light.rs) to see them in action.

crates/bevy_internal/Cargo.toml

@@ -85,6 +85,9 @@ bluenoise_texture = ["bevy_pbr?/bluenoise_texture", "ktx2", "bevy_image/zstd"]
 # Include a preintegrated BRDF Look Up Table for more accurate specular shading.
 dfg_lut = ["bevy_pbr?/dfg_lut", "ktx2", "bevy_image/zstd"]
 
+# Include Look Up Tables that are required for area lights.
+area_light_luts = ["bevy_pbr?/area_light_luts", "ktx2", "bevy_image/zstd"]
+
 # NVIDIA Deep Learning Super Sampling
 dlss = ["bevy_anti_alias/dlss", "bevy_solari?/dlss"]
 

crates/bevy_light/src/rect_light.rs

@@ -13,6 +13,8 @@ use crate::light_consts;
 ///
 /// Shadow maps are currently unsupported, objects illuminated by a
 /// ``RectLight`` will not cast shadows.
+///
+/// Note: Requires the `area_light_luts` cargo feature.
 #[derive(Component, Debug, Clone, Copy, Reflect)]
 #[reflect(Component, Default, Debug, Clone)]
 #[require(Transform, Visibility, VisibilityClass)]

crates/bevy_pbr/Cargo.toml

@@ -22,6 +22,7 @@ pbr_clustered_decals = []
 pbr_light_textures = []
 bluenoise_texture = ["bevy_image/ktx2", "bevy_image/zstd"]
 dfg_lut = ["bevy_image/ktx2", "bevy_image/zstd"]
+area_light_luts = ["bevy_image/ktx2", "bevy_image/zstd"]
 shader_format_glsl = ["bevy_shader/shader_format_glsl"]
 trace = ["bevy_render/trace"]
 # Enables the meshlet renderer for dense high-poly scenes (experimental)

crates/bevy_pbr/src/lib.rs

@@ -107,14 +107,14 @@ use bevy_asset::{AssetApp, AssetPath, Assets, Handle, RenderAssetUsages};
 use bevy_core_pipeline::mip_generation::experimental::depth::early_downsample_depth;
 use bevy_core_pipeline::schedule::{Core3d, Core3dSystems};
 use bevy_ecs::prelude::*;
-use bevy_image::{CompressedImageFormats, Image, ImageSampler, ImageType};
+use bevy_image::{Image, ImageSampler};
 use bevy_material::AlphaMode;
 use bevy_render::{
     camera::sort_cameras,
     extract_resource::ExtractResourcePlugin,
     render_resource::{
         Extent3d, TextureDataOrder, TextureDescriptor, TextureDimension, TextureFormat,
-        TextureUsages,
+        TextureUsages, TextureViewDescriptor, TextureViewDimension,
     },
     sync_component::SyncComponentPlugin,
     ExtractSchedule, GpuResourceAppExt, Render, RenderApp, RenderDebugFlags, RenderStartup,
@@ -169,14 +169,14 @@ pub struct Bluenoise {
 
 /// LTC (Linearly Transformed Cosines) LUT textures for area light shading.
 ///
-/// `ltc_1` encodes the 4 non-trivial elements of the inverse GGX LTC matrix.
-/// `ltc_2` encodes amplitude and Fresnel-related weights.
+/// It is a texture array containing 2 LUT textures:
+/// The first entry encodes the 4 non-trivial elements of the inverse GGX LTC matrix.
+/// The second entry encodes amplitude and Fresnel-related weights.
 ///
 /// [LUT source and fitting code](https://github.com/selfshadow/ltc_code/blob/master/fit/results)
 #[derive(Resource, Clone)]
-pub struct LtcLuts {
-    pub ltc_1: Handle<Image>,
-    pub ltc_2: Handle<Image>,
+pub struct AreaLightLuts {
+    pub image: Handle<Image>,
 }
 
 // See https://github.com/bevyengine/bevy/pull/23737 for information on how the LUT was generated.
@@ -282,15 +282,16 @@ impl Plugin for PbrPlugin {
             let mut images = app.world_mut().resource_mut::<Assets<Image>>();
             #[cfg(feature = "bluenoise_texture")]
             let handle = {
-                let image = Image::from_buffer(
+                let mut image = Image::from_buffer(
                     include_bytes!("bluenoise/stbn.ktx2"),
-                    ImageType::Extension("ktx2"),
-                    CompressedImageFormats::NONE,
+                    bevy_image::ImageType::Extension("ktx2"),
+                    bevy_image::CompressedImageFormats::NONE,
                     false,
                     ImageSampler::Default,
                     RenderAssetUsages::RENDER_WORLD,
                 )
                 .expect("Failed to decode embedded blue-noise texture");
+                image.texture_descriptor.label = Some("bluenoise");
                 images.add(image)
             };
 
@@ -304,39 +305,32 @@ impl Plugin for PbrPlugin {
             }
         }
 
-        let has_ltc_luts = app
+        let has_area_light_luts = app
             .get_sub_app(RenderApp)
-            .is_some_and(|render_app| render_app.world().is_resource_added::<LtcLuts>());
+            .is_some_and(|render_app| render_app.world().is_resource_added::<AreaLightLuts>());
 
-        if !has_ltc_luts {
+        if !has_area_light_luts {
             let mut images = app.world_mut().resource_mut::<Assets<Image>>();
-            let ltc_luts = LtcLuts {
-                ltc_1: images.add(
-                    Image::from_buffer(
-                        include_bytes!("ltc/ltc1.ktx2"),
-                        ImageType::Extension("ktx2"),
-                        CompressedImageFormats::NONE,
-                        false,
-                        ImageSampler::linear(),
-                        RenderAssetUsages::RENDER_WORLD,
-                    )
-                    .expect("Failed to decode embedded LTC LUT 1"),
-                ),
-                ltc_2: images.add(
-                    Image::from_buffer(
-                        include_bytes!("ltc/ltc2.ktx2"),
-                        ImageType::Extension("ktx2"),
-                        CompressedImageFormats::NONE,
-                        false,
-                        ImageSampler::linear(),
-                        RenderAssetUsages::RENDER_WORLD,
-                    )
-                    .expect("Failed to decode embedded LTC LUT 2"),
-                ),
+            #[cfg(feature = "area_light_luts")]
+            let handle = {
+                let mut image = Image::from_buffer(
+                    include_bytes!("ltc/ltc.ktx2"),
+                    bevy_image::ImageType::Extension("ktx2"),
+                    bevy_image::CompressedImageFormats::NONE,
+                    false,
+                    ImageSampler::linear(),
+                    RenderAssetUsages::RENDER_WORLD,
+                )
+                .expect("Failed to decode embedded LTC LUTs");
+                image.texture_descriptor.label = Some("area_light_luts");
+                images.add(image)
             };
+            #[cfg(not(feature = "area_light_luts"))]
+            let handle = images.add(area_light_luts_placeholder());
 
+            let area_light_luts = AreaLightLuts { image: handle };
             if let Some(render_app) = app.get_sub_app_mut(RenderApp) {
-                render_app.world_mut().insert_resource(ltc_luts);
+                render_app.world_mut().insert_resource(area_light_luts);
             }
         }
 
@@ -349,8 +343,8 @@ impl Plugin for PbrPlugin {
             let texture = app.world_mut().resource_mut::<Assets<Image>>().add(
                 Image::from_buffer(
                     include_bytes!("environment_map/dfg.ktx2"),
-                    ImageType::Extension("ktx2"),
-                    CompressedImageFormats::NONE,
+                    bevy_image::ImageType::Extension("ktx2"),
+                    bevy_image::CompressedImageFormats::NONE,
                     false,
                     ImageSampler::linear(),
                     RenderAssetUsages::RENDER_WORLD,
@@ -468,7 +462,7 @@ pub fn stbn_placeholder() -> Image {
             size: Extent3d::default(),
             format,
             dimension: TextureDimension::D2,
-            label: None,
+            label: Some("bluenoise_placeholder"),
             mip_level_count: 1,
             sample_count: 1,
             usage: TextureUsages::TEXTURE_BINDING,
@@ -481,6 +475,36 @@ pub fn stbn_placeholder() -> Image {
     }
 }
 
+pub fn area_light_luts_placeholder() -> Image {
+    let format = TextureFormat::Rgba16Float;
+    let data = vec![0; 16];
+    Image {
+        data: Some(data),
+        data_order: TextureDataOrder::default(),
+        texture_descriptor: TextureDescriptor {
+            size: Extent3d {
+                width: 1,
+                height: 1,
+                depth_or_array_layers: 2,
+            },
+            format,
+            dimension: TextureDimension::D2,
+            label: Some("area_light_luts_placeholder"),
+            mip_level_count: 1,
+            sample_count: 1,
+            usage: TextureUsages::TEXTURE_BINDING,
+            view_formats: &[],
+        },
+        sampler: ImageSampler::Default,
+        texture_view_descriptor: Some(TextureViewDescriptor {
+            dimension: Some(TextureViewDimension::D2Array),
+            ..Default::default()
+        }),
+        asset_usage: RenderAssetUsages::RENDER_WORLD,
+        copy_on_resize: false,
+    }
+}
+
 impl SyncComponent<PbrPlugin> for DirectionalLight {
     type Target = (
         Self,

crates/bevy_pbr/src/render/light.rs

@@ -420,6 +420,7 @@ pub fn extract_lights(
         &mut RenderExtractedShadowMapVisibleEntities,
         &mut RenderShadowMapVisibleEntities,
     )>,
+    mut rect_light_missing_luts_warning_emitted: Local<bool>,
 ) {
     let mapper = &visibility_extraction_system_param.mapper;
 
@@ -824,6 +825,12 @@ pub fn extract_lights(
     }
 
     for (main_entity, render_entity, rect_light, transform, view_visibility) in &rect_lights {
+        if !cfg!(feature = "area_light_luts") && !*rect_light_missing_luts_warning_emitted {
+            warn!(
+                "RectLight will not work properly because the `area_light_luts` cargo feature is not enabled."
+            );
+            *rect_light_missing_luts_warning_emitted = true;
+        }
         if !view_visibility.get() {
             if let Ok(mut entity_commands) = commands.get_entity(render_entity) {
                 entity_commands.remove::<ExtractedRectLight>();

crates/bevy_pbr/src/render/mesh.rs

@@ -3344,6 +3344,9 @@ impl SpecializedMeshPipeline for MeshPipeline {
         if cfg!(feature = "dfg_lut") {
             shader_defs.push("DFG_LUT".into());
         }
+        if cfg!(feature = "area_light_luts") {
+            shader_defs.push("AREA_LIGHT_LUTS".into());
+        }
 
         let bind_group_layout = self.get_view_layout(key.into());
         let mut bind_group_layout = vec![

crates/bevy_pbr/src/render/mesh_view_bindings.rs

@@ -1,5 +1,5 @@
 use crate::{
-    DfgLut, LtcLuts, ScreenSpaceTransmission, ViewEnvironmentMapUniformOffset,
+    AreaLightLuts, DfgLut, ScreenSpaceTransmission, ViewEnvironmentMapUniformOffset,
     ViewFogUniformOffset, ViewLightProbesUniformOffset, ViewLightsUniformOffset,
     ViewScreenSpaceReflectionsUniformOffset,
 };
@@ -97,6 +97,7 @@ bitflags::bitflags! {
         const SCREEN_SPACE_TRANSMISSION        = 1 << 13;
         const CONTACT_SHADOWS                  = 1 << 14;
         const DISTANCE_FOG                     = 1 << 15;
+        const AREA_LIGHT_LUTS                         = 1 << 16;
     }
 }
 
@@ -150,6 +151,10 @@ impl From<MeshPipelineKey> for MeshPipelineViewLayoutKey {
             result |= MeshPipelineViewLayoutKey::STBN;
         }
 
+        if cfg!(feature = "area_light_luts") {
+            result |= MeshPipelineViewLayoutKey::AREA_LIGHT_LUTS;
+        }
+
         if value.contains(MeshPipelineKey::TONEMAP_IN_SHADER) {
             result |= MeshPipelineViewLayoutKey::TONEMAP_IN_SHADER;
         }
@@ -462,25 +467,23 @@ fn layout_entries(
         ),));
     }
     // LTC LUTs for area lights
-    entries = entries.extend_with_indices((
-        (
-            36,
-            texture_2d(TextureSampleType::Float { filterable: true }),
-        ),
-        (
-            37,
-            texture_2d(TextureSampleType::Float { filterable: true }),
-        ),
-        (38, sampler(SamplerBindingType::Filtering)),
-    ));
+    if cfg!(feature = "area_light_luts") {
+        entries = entries.extend_with_indices((
+            (
+                36,
+                texture_2d_array(TextureSampleType::Float { filterable: true }),
+            ),
+            (37, sampler(SamplerBindingType::Filtering)),
+        ));
+    }
     // DFG LUT
     if cfg!(feature = "dfg_lut") {
         entries = entries.extend_with_indices((
             (
-                39,
+                38,
                 texture_2d(TextureSampleType::Float { filterable: true }),
             ),
-            (40, sampler(SamplerBindingType::Filtering)),
+            (39, sampler(SamplerBindingType::Filtering)),
         ));
     }
 
@@ -678,7 +681,7 @@ pub fn prepare_mesh_view_bind_groups(
         atmosphere_buffer,
         atmosphere_sampler,
         blue_noise,
-        ltc_luts,
+        area_light_luts,
         dfg_lut,
     ): (
         Res<DecalsBuffer>,
@@ -686,7 +689,7 @@ pub fn prepare_mesh_view_bind_groups(
         Option<Res<AtmosphereBuffer>>,
         Option<Res<AtmosphereSampler>>,
         Res<Bluenoise>,
-        Res<LtcLuts>,
+        Res<AreaLightLuts>,
         Res<DfgLut>,
     ),
     // TODO: Figure out how to reuse the memory. `BindGroupEntry` is non-send on wasm with atomics.
@@ -896,16 +899,16 @@ pub fn prepare_mesh_view_bind_groups(
             };
 
             // LTC LUTs for area lights
-            let (ltc1_view, ltc_sampler) = images
-                .get(&ltc_luts.ltc_1)
-                .map(|img| (&img.texture_view, &img.sampler))
-                .unwrap_or((&fallback_image.d2.texture_view, &fallback_image.d2.sampler));
-            let ltc2_view = images
-                .get(&ltc_luts.ltc_2)
-                .map(|img| &img.texture_view)
-                .unwrap_or(&fallback_image.d2.texture_view);
-            entries =
-                entries.extend_with_indices(((36, ltc1_view), (37, ltc2_view), (38, ltc_sampler)));
+            if cfg!(feature = "area_light_luts") {
+                let (ltc_view, ltc_sampler) = images
+                    .get(&area_light_luts.image)
+                    .map(|img| (&img.texture_view, &img.sampler))
+                    .unwrap_or((
+                        &fallback_image.d2_array.texture_view,
+                        &fallback_image.d2_array.sampler,
+                    ));
+                entries = entries.extend_with_indices(((36, ltc_view), (37, ltc_sampler)));
+            }
 
             // DFG LUT
             if cfg!(feature = "dfg_lut") {
@@ -913,7 +916,7 @@ pub fn prepare_mesh_view_bind_groups(
                     .get(&dfg_lut.texture)
                     .map(|img| (&img.texture_view, &img.sampler))
                     .unwrap_or((&fallback_image.d2.texture_view, &fallback_image.d2.sampler));
-                entries = entries.extend_with_indices(((39, dfg_view), (40, dfg_sampler)));
+                entries = entries.extend_with_indices(((38, dfg_view), (39, dfg_sampler)));
             }
 
             let environment_map_bind_group_entries =

crates/bevy_pbr/src/render/mesh_view_bindings.wgsl

@@ -121,16 +121,19 @@ const VISIBILITY_RANGE_UNIFORM_BUFFER_SIZE: u32 = 64u;
 @group(0) @binding(33) var atmosphere_transmittance_sampler: sampler;
 @group(0) @binding(34) var<storage> atmosphere: atmosphere_types::Atmosphere;
 #endif // ATMOSPHERE
+
 #ifdef BLUE_NOISE_TEXTURE
 @group(0) @binding(35) var blue_noise_texture: texture_2d_array<f32>;
 #endif // BLUE_NOISE_TEXTURE
 
-@group(0) @binding(36) var ltc_lut1: texture_2d<f32>;
-@group(0) @binding(37) var ltc_lut2: texture_2d<f32>;
-@group(0) @binding(38) var ltc_lut_sampler: sampler;
+#ifdef AREA_LIGHT_LUTS
+@group(0) @binding(36) var area_light_luts: texture_2d_array<f32>;
+@group(0) @binding(37) var area_light_luts_sampler: sampler;
+#endif
+
 #ifdef DFG_LUT
-@group(0) @binding(39) var dfg_lut: texture_2d<f32>;
-@group(0) @binding(40) var dfg_lut_sampler: sampler;
+@group(0) @binding(38) var dfg_lut: texture_2d<f32>;
+@group(0) @binding(39) var dfg_lut_sampler: sampler;
 #endif // DFG_LUT
 
 #ifdef ENVIRONMENT_MAP

crates/bevy_pbr/src/render/pbr_functions.wgsl

@@ -657,6 +657,7 @@ fn apply_pbr_lighting(
 #endif
     }
 
+#ifdef AREA_LIGHT_LUTS
     // Rect lights
     let n_rect_lights = view_bindings::lights.n_rect_lights;
     for (var i: u32 = 0u; i < n_rect_lights; i = i + 1u) {
@@ -670,6 +671,7 @@ fn apply_pbr_lighting(
         transmitted_light += transmitted_light_contrib;
     #endif
     }
+#endif
 
 #ifdef STANDARD_MATERIAL_DIFFUSE_TRANSMISSION
     // NOTE: We use the diffuse transmissive color, the second Lambertian lobe's calculated

crates/bevy_pbr/src/render/pbr_lighting.wgsl

@@ -1010,6 +1010,7 @@ fn ltc_integrate_quad(
     return sum;
 }
 
+#ifdef AREA_LIGHT_LUTS
 fn rect_light(
     light_id: u32,
     input: ptr<function, LightingInput>,
@@ -1046,8 +1047,8 @@ fn rect_light(
     let LUT_SCALE = 63.0 / 64.0;
     let LUT_BIAS  =  0.5 / 64.0;
     let uv = vec2<f32>(perceptual_roughness, sqrt(1.0 - NdotV)) * LUT_SCALE + LUT_BIAS;
-    let t1 = textureSampleLevel(view_bindings::ltc_lut1, view_bindings::ltc_lut_sampler, uv, 0.0);
-    let t2 = textureSampleLevel(view_bindings::ltc_lut2, view_bindings::ltc_lut_sampler, uv, 0.0);
+    let t1 = textureSampleLevel(view_bindings::area_light_luts, view_bindings::area_light_luts_sampler, uv, 0, 0.0);
+    let t2 = textureSampleLevel(view_bindings::area_light_luts, view_bindings::area_light_luts_sampler, uv, 1, 0.0);
 
     // Reconstruct the GGX inverse-LTC matrix
     let Minv = mat3x3<f32>(
@@ -1077,8 +1078,8 @@ fn rect_light(
 
     // Sample LUTs for clearcoat layer
     let cc_uv = vec2<f32>(clearcoat_perceptual_roughness, sqrt(1.0 - clearcoat_NdotV)) * LUT_SCALE + LUT_BIAS;
-    let tc1 = textureSampleLevel(view_bindings::ltc_lut1, view_bindings::ltc_lut_sampler, cc_uv, 0.0);
-    let tc2 = textureSampleLevel(view_bindings::ltc_lut2, view_bindings::ltc_lut_sampler, cc_uv, 0.0);
+    let tc1 = textureSampleLevel(view_bindings::area_light_luts, view_bindings::area_light_luts_sampler, cc_uv, 0, 0.0);
+    let tc2 = textureSampleLevel(view_bindings::area_light_luts, view_bindings::area_light_luts_sampler, cc_uv, 1, 0.0);
     let Minv_cc = mat3x3<f32>(
         vec3<f32>(tc1.x, 0.0, tc1.y),
         vec3<f32>(0.0,   1.0, 0.0),
@@ -1097,6 +1098,7 @@ fn rect_light(
     return (spec_weight * spec + diffuse_color * diff) * (*light).color.rgb * range_falloff;
 #endif
 }
+#endif
 
 
 #ifdef ATMOSPHERE

crates/bevy_pbr/src/ssr/mod.rs

@@ -514,6 +514,9 @@ impl SpecializedRenderPipeline for ScreenSpaceReflectionsPipeline {
         if cfg!(feature = "dfg_lut") {
             shader_defs.push("DFG_LUT".into());
         }
+        if cfg!(feature = "area_light_luts") {
+            shader_defs.push("AREA_LIGHT_LUTS".into());
+        }
 
         #[cfg(not(target_arch = "wasm32"))]
         shader_defs.push("USE_DEPTH_SAMPLERS".into());

docs/cargo_features.md

@@ -62,6 +62,7 @@ This is the complete `bevy` cargo feature list, without "profiles" or "collectio
 |accesskit_unix|Enable AccessKit on Unix backends (currently only works with experimental screen readers and forks.)|
 |android-game-activity|Android GameActivity support. Default, choose between this and `android-native-activity`.|
 |android-native-activity|Android NativeActivity support. Legacy, should be avoided for most new Android games.|
+|area_light_luts|Include Look Up Tables that are required for area lights.|
 |asset_processor|Enables the built-in asset processor for processed assets.|
 |async-io|Use async-io's implementation of block_on instead of futures-lite's implementation. This is preferred if your application uses async-io.|
 |async_executor|Uses `async-executor` as a task execution backend.|