Added Light Falloff Curves

[GageHowe]

N/A IN PROGRESS

[GageHowe]

[Copilot]

Pull request overview

This PR introduces configurable distance falloff curves for punctual lights (point + spot) and wires those modes through clustered lighting on both the Rust and WGSL sides, with an accompanying example to visualize the differences.

Changes:

• Add LightFalloff (InverseSquare / Linear / Exponential) and expose it on PointLight and SpotLight (defaulting to inverse-square).
• Encode falloff mode into GPU light flags, update clustered-light ordering/bucketing, and update PBR + volumetric fog shaders to apply the correct attenuation per light.
• Add a new examples/3d/light_falloff.rs example and register it in Cargo.toml.

Reviewed changes

Copilot reviewed 17 out of 17 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
examples/3d/light_falloff.rs	New example demonstrating point/spot light falloff modes with simple controls/UI.
crates/bevy_pbr/src/volumetric_fog/volumetric_fog.wgsl	Apply falloff-aware distance attenuation for volumetric fog lighting.
crates/bevy_pbr/src/render/pbr_lighting.wgsl	Split distance attenuation into inverse-square/linear/exponential helpers and route point/spot lighting accordingly.
crates/bevy_pbr/src/render/pbr_functions.wgsl	Iterate lights by falloff buckets (SSBO path) and branch by falloff (fallback path).
crates/bevy_pbr/src/render/mesh_view_types.wgsl	Define falloff flag encoding constants and expand SSBO cluster offsets/counts layout.
crates/bevy_pbr/src/render/light.rs	Extract/store falloff on lights; encode falloff into GPU flags; include falloff in clusterable object types.
crates/bevy_pbr/src/render/clustered_forward.wgsl	Update SSBO cluster range unpacking for falloff-bucketed point/spot lights.
crates/bevy_pbr/src/cluster/mod.rs	Expand GPU cluster offset/count storage to 3 UVec4s and write per-falloff counts on SSBO targets.
crates/bevy_pbr/src/cluster/cluster_raster.wgsl	Bucket point/spot lights by falloff during GPU clustering and update scratch counters/layout.
crates/bevy_pbr/src/cluster/cluster_allocate.wgsl	Zero/size/update cluster count buffers for the expanded SSBO layout.
crates/bevy_light/src/spot_light.rs	Add falloff: LightFalloff to SpotLight with default.
crates/bevy_light/src/point_light.rs	Add falloff: LightFalloff to PointLight with default.
crates/bevy_light/src/light_falloff.rs	New LightFalloff enum with stable shader/bucketing indices.
crates/bevy_light/src/lib.rs	Export LightFalloff (including in the prelude).
crates/bevy_light/src/cluster/mod.rs	Track per-falloff point/spot counts per cluster and plumb falloff into add_* helpers.
crates/bevy_light/src/cluster/assign.rs	Include falloff in clusterable light types and ordering so falloff bucketing is stable.
Cargo.toml	Register the new light_falloff example metadata.

Comments suppressed due to low confidence (2)

crates/bevy_pbr/src/cluster/cluster_raster.wgsl:523

• In GPU clustering (POPULATE_PASS), the irradiance volume base offset does not include the reflection-probe count (offsets_and_counts.data[cluster_index][1u].w). This will make irradiance volumes write into the reflection-probe segment instead of after it. Include the reflection-probe count in the computed offset.

        case CLUSTERABLE_OBJECT_TYPE_IRRADIANCE_VOLUME: {
            return offsets_and_counts.data[cluster_index][0u].x +
                offsets_and_counts.data[cluster_index][0u].y +
                offsets_and_counts.data[cluster_index][0u].z +
                offsets_and_counts.data[cluster_index][0u].w +
                offsets_and_counts.data[cluster_index][1u].x +
                offsets_and_counts.data[cluster_index][1u].y +
                offsets_and_counts.data[cluster_index][1u].z +
                atomicAdd(
                    &scratchpad_offsets_and_counts.data[cluster_index].irradiance_volumes,
                    1u
                );
        }

crates/bevy_pbr/src/cluster/cluster_raster.wgsl:532

• In GPU clustering (POPULATE_PASS), the decal base offset currently excludes both the reflection-probe count (offsets_and_counts.data[cluster_index][1u].w) and the irradiance-volume count (offsets_and_counts.data[cluster_index][2u].x). This will cause decals to overwrite earlier segments. Update the offset expression so decals start after point lights + spot lights + reflection probes + irradiance volumes.

        case CLUSTERABLE_OBJECT_TYPE_DECAL: {
            return offsets_and_counts.data[cluster_index][0u].x +
                offsets_and_counts.data[cluster_index][0u].y +
                offsets_and_counts.data[cluster_index][0u].z +
                offsets_and_counts.data[cluster_index][0u].w +
                offsets_and_counts.data[cluster_index][1u].x +
                offsets_and_counts.data[cluster_index][1u].y +
                offsets_and_counts.data[cluster_index][1u].z +
                atomicAdd(&scratchpad_offsets_and_counts.data[cluster_index].decals, 1u);

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