Fix HALFRES compositer darkening background behind transparent geometry

[coobeeyon]

Problem

When halfRes is enabled, the EffectCompositer's HALFRES code path hardcodes vec4(0.0, 0.0, 0.0, 1.0) for far-plane pixels (depth == 1.0). The R channel value of 0.0 is interpreted as full ambient occlusion, which darkens the entire background when transparent objects with depthWrite disabled leave far-plane depth values in the depth buffer.

Fix

Replace the hardcoded constant with texture2D(tDiffuse, vUv), which bilinearly samples the AO buffer. For background pixels the AO pass already writes 1.0 (no occlusion) via the early return in the EffectShader, so the sampled value is correct. This also provides smooth edge transitions at geometry boundaries — the hardcoded constant created a visible halo where the binary depth == 1.0 check met the upsampled AO values.

Reproduction

1. Render a scene with halfRes: true
2. Set some geometry to transparent with depthWrite: false
3. Observe the background behind transparent geometry is darkened
4. With halfRes: false, the background renders correctly

Change

One-line change in src/EffectCompositer.js:

-            texel = vec4(0.0, 0.0, 0.0, 1.0);
+            texel = texture2D(tDiffuse, vUv);