Module rendering/post-processing/bloom/shaders

Bloom pyramid shader sources.

Three fullscreen passes share a unit-triangle vertex shader:

• threshold + 2× downsample → mip[0]
• plain 2× downsample → mip[i+1]
• 4-tap tent upsample → mip[i] (additive blend)

Source-of-truth lives here so the eventual WebGPU/TSL port has one place to add NodeMaterial factories without touching chain.ts.