GPU Pro 3 sample of bent cones screen space ambient occlusion.

screenspacebentconesao.glsl

void main()
{
  vec3 positionX = backproject(depthTexture(pixelCoordinateI), inverseViewProjectionMatrix);
  vec3 normalX = normalTexture(pixelCoordinateI);
  // get ONB to transform samples
  mat3 orthoNormalBasis = computeONB(normalX);
  // select samples for pixel out of pattern
  int patternOffset = getPatternOffset(pixelCoordinateI);

  float ao = 0.0;
  int validAODirectionCount = 0;
  vec3 bentNormal = vec3(0.0);
  float unocclutedDirections = 0.0;

  for (int index = 0; index < sampleCount; ++index)
  {
    vec3 sampleDirection = orthoNormalBasis * getSampleDirection(index, patternOffset);
    bool isOutlier = false;
    // use float instead of bool and
    // apply a fall off function to get smooth AO
    float visibility = 1.0;
    // this function tests for occlusion in SS
    // depending on the actual technique
    // and sample distribution
    // the implementation of this function varies
    checkSSVisibilityWithRayMarchingSmooth(
        sampleDirection, maxOccluderDistance,
        depthTexture, inverseViewProjectionMatrix,
        positionX, normalX,
        rayMarchingSteps, rayMarchingStartOffset
        visibility, isOutlier);

    // we have insufficient information in SS
    // here we simply ignore samples
    // which can't be handled properly
    if (!isOutlier)
    {
      validAODirectionCount++;
      ao += visibility;
    }

    // for bent normals, we assume,
    // that outlier occluders are NOT real occluders!
    // sum up unoccluded directions
    // direction may be partially visibile
    // => only counts accordingly
    bentNormal += normalize(sampleDirection) * visibility;
    unoccludedDirections += visibility;
  }

  ao /= float(validAODirectionCount);
  bentNormal /= unoccludedDirections;
}