Module rendering/post-processing/bloom/chain

Bloom pyramid: downsample + upsample chain producing a soft-glow texture from an HDR scene.

Standard mipmap-blur pattern (Next-Gen Post Processing, GDC 2015):

1. Threshold + 2× downsample → mip[0]
2. For i in 0..levels-2: 2× downsample mip[i] → mip[i+1]
3. For i in levels-2..0: additively upsample mip[i+1] into mip[i] using a 4-tap tent filter (cheap, smooth, no banding)

Output: outputTexture (= mip[0]). The mega-shader samples this and adds it onto the scene color (additive blend).

Bloom resolution is half the canvas. Bloom is a soft glow; full-res doesn't visibly improve quality and doubles memory.