message: Fix depth mipmaping program
  Due to a typo, we were using a nearest neighbor downsampling, instead
  of picking one of the 4 pixels based on position.
diff: @@ -20,9 +20,12 @@ material {
  }
  fragment {
  + // We use a rotated grid sub-sample as it's cheap and gives good results
  + // See Scalable Ambient Obscurance by McGuire and al.
  void postProcess(inout PostProcessInputs postProcess) {
  int level = materialParams.level;
  - ivec2 xy = ivec2(gl_FragCoord.xy) * 2;
  - gl_FragDepth = texelFetch(materialParams_depth, xy + ivec2(xy.x & 1, xy.y & 1), level).r;
  + ivec2 icoord = ivec2(gl_FragCoord.xy);
  + gl_FragDepth = texelFetch(materialParams_depth,
  + 2 * icoord + ivec2(icoord.y & 1, icoord.x & 1), level).r;
  }
  }
  