feat: support dynamic work buffer formats in compute GSplat renderers

[mvaligursky]

Compute tiled GSplat renderers now dynamically support different work buffer formats (compact and large) instead of hardcoding the compact format's texture bindings and decode logic.

Changes:

• Add getComputeInputDeclarations() and getComputeBindFormats() to GSplatFormat for generating compute shader bindings and declarations from format metadata (including extra streams like pcId, pcNodeIndex)
• Replace hardcoded texture bindings and decode functions in compute tile-count shaders with format-generated #include directives (gsplatComputeSplatCS, gsplatFormatDeclCS, gsplatFormatReadCS)
• Remove compact-specific decodeRotation(), decodeScale(), decodeColor() from compute-gsplat-common.js — format read chunks now handle all decoding
• Derive formatStartBinding from fixed bindings array length instead of hardcoding magic numbers
• Recreate compute shaders when work buffer format changes at runtime (tracked via format hash), with consolidated recreation to avoid redundant double-recreation per frame
• Set GSPLAT_COLOR_FLOAT define for non-RGBA16U color formats to use the correct float reading path
• Clamp negative color values before gamma decoding to prevent NaN from pow() on negative inputs, matching the quad renderer

Compact format repack:

• Co-locate alpha with center position in dataTransformA (scale.xyz 3×8-bit + alpha 8-bit), move rotation to dataTransformB
• Enables single-texture opacity early-out in compute shaders — culled splats skip dataColor and dataTransformB loads entirely

Work buffer getOpacity()/getColor() API:

• Add getOpacity() to both work buffer format readers for early culling before loading color data
• Change getColor() to return vec3 (RGB only) for both work buffer formats; opacity handled separately via getOpacity()
• Large format: getOpacity() unconditionally loads and caches color (no conditional branch); getColor() returns cached RGB
• Compact format: getOpacity() reads alpha from cachedTransformA (no extra texture load); getColor() returns decoded RGB
• Quad VS uses GSPLAT_SEPARATE_OPACITY define to call getOpacity() before getColor() when rendering from work buffer
• Strict call order: getCenter() → getOpacity() → getColor() for all work buffer consumers (compute shaders and quad VS)

Performance:

• Fixed bindings precede format-specific bindings so format textures are always last, keeping binding indices stable
• Early opacity culling in compute tile-count shaders avoids unnecessary texture loads for transparent splats

[Copilot]

Pull request overview

This PR updates the unified compute-based GSplat renderers to work with multiple work-buffer layouts (compact vs large/packed) by generating compute shader bindings/declarations and read/decode logic from GSplatFormat metadata instead of hardcoding compact-only streams and decoders.

Changes:

• Add compute-specific stream declaration/bind-format generation on GSplatFormat, and new WGSL helper chunks for compute splat indexing + explicit bindings.
• Refactor compute tile-count shaders to use format-provided declarations/read code and clamp negative color before gamma conversion.
• Recreate compute shaders when the work-buffer format (hash) or tonemap/gamma changes, consolidating recreation triggers.

Reviewed changes

Copilot reviewed 8 out of 8 changed files in this pull request and generated 7 comments.

Show a summary per file

File	Description
src/scene/shader-lib/wgsl/chunks/gsplat/vert/gsplatComputeStreamDecl.js	New WGSL template to declare compute-bound stream textures with explicit @binding and load helpers.
src/scene/shader-lib/wgsl/chunks/gsplat/vert/gsplatComputeSplat.js	New WGSL chunk providing a compute-compatible Splat struct and setSplat() helper.
src/scene/shader-lib/wgsl/chunks/gsplat/compute-gsplat-tile-count.js	Switch to format-generated declarations/read code and remove compact-specific decode paths; clamp color before gamma.
src/scene/shader-lib/wgsl/chunks/gsplat/compute-gsplat-local-tile-count.js	Same as global tile-count, updated for the local/compacted-ID path.
src/scene/shader-lib/wgsl/chunks/gsplat/compute-gsplat-common.js	Remove compact-only decode helpers now replaced by format read chunks.
src/scene/gsplat/gsplat-format.js	Add getComputeInputDeclarations() and getComputeBindFormats() to generate compute bindings from format metadata.
src/scene/gsplat-unified/gsplat-compute-local-renderer.js	Bind all format streams dynamically and recreate count compute when format hash/tonemap/gamma changes.
src/scene/gsplat-unified/gsplat-compute-global-renderer.js	Same dynamic binding + recreation logic for the global compute renderer.

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[Copilot]

Pull request overview

Copilot reviewed 18 out of 18 changed files in this pull request and generated no new comments.

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