RT→rgba16float→threshold→blur→composite, end-to-end proof of the three
primitives. threshold/blur run from onBeforeUpdate (one submit each) so the
storage-write→sampled-read dependency gets WebGPU's per-submit barrier
(there is none between dispatches within a compute pass); the composite is a
UI custom shader so it owns the canvas ping-pong. Documents the Vulkan
symmetry (gap 4): the native present path records passes generically and
barriers between them, so the same chain is wireable today.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Adds the minimal WebGPU-backend surface an HDR bloom/post chain needs:
1. wgpuCreateStorageImage2D + StorageImage2D<>: runtime rgba16float (or
other format) textures with STORAGE_BINDING|TEXTURE_BINDING usage, no
CompressedTextureAsset upload — GPU-produced HDR targets.
2. UICustomBindingKind::StorageTexture (kind 5): write-only storage-texture
binding carrying a texel format (the freed UICustomBinding::format byte),
wired through all three binding paths (UI custom / RT / plain compute).
Float textures already sample via SampledTexture (sampleType float).
3. PipelineRTWebGPU::Init(..., hdrOutputFormat): RESOLVE writes the linear
accumulator into a user rgba16float texture (RTPass::outTexHandle)
instead of the rgba8unorm canvas, leaving the composite→swapchain pass to
the app. Default RGBA8Unorm keeps the canvas path byte-identical.
Existing RT examples updated for the _pad→format field rename; the default
paths are unchanged (verified RTStress builds + renders).
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
