message: more efficient depth mipmaping
  We simply pick one of the 4 depth texel based on its screen
  space offset. Literature showed it doesn't impact AO
  significantly.
diff: @@ -24,23 +24,8 @@ material {
  fragment {
  void material(inout MaterialInputs material) {
  prepareMaterial(material);
  -
  int level = materialParams.level;
  ivec2 xy = ivec2(gl_FragCoord.xy) * 2;
  - highp float d00 = texelFetch(materialParams_depth, xy + ivec2(0, 0), level).r;
  - highp float d10 = texelFetch(materialParams_depth, xy + ivec2(1, 0), level).r;
  - highp float d01 = texelFetch(materialParams_depth, xy + ivec2(0, 1), level).r;
  - highp float d11 = texelFetch(materialParams_depth, xy + ivec2(1, 1), level).r;
  -
  - gl_FragDepth =
  -
  - // conservative occlusion
  - //max(d00, max(d01, max(d10, d11)));
  -
  - // conservative visibility
  - //min(d00, min(d01, min(d10, d11)));
  -
  - // arithmetic mean: preserve screen-space area
  - (d00 + d01 + d10 + d11) * 0.25;
  + gl_FragDepth = texelFetch(materialParams_depth, xy + ivec2(xy.x & 1, xy.y & 1), level).r;
  }
  }
  