Duckstation/src/util/metal_shaders.metal

/// A custom resolve kernel that averages color at all sample points.
#include <metal_stdlib>
using namespace metal;

// https://developer.apple.com/documentation/metal/metal_sample_code_library/improving_edge-rendering_quality_with_multisample_antialiasing_msaa?language=objc
kernel void
colorResolveKernel(texture2d_ms<float, access::read> multisampledTexture [[texture(0)]],
                   texture2d<float, access::write> resolvedTexture [[texture(1)]],
                   uint2 gid [[thread_position_in_grid]])
{
    const uint count = multisampledTexture.get_num_samples();
    
    float4 resolved_color = 0;
    
    for (uint i = 0; i < count; ++i)
    {
        resolved_color += multisampledTexture.read(gid, i);
    }
    
    resolved_color /= count;
    
    resolvedTexture.write(resolved_color, gid);
}

kernel void
depthResolveKernel(texture2d_ms<float, access::read> multisampledTexture [[texture(0)]],
                   texture2d<float, access::write> resolvedTexture [[texture(1)]],
                   uint2 gid [[thread_position_in_grid]])
{
  const uint count = multisampledTexture.get_num_samples();
  
  float resolved_depth = 0;
  
  for (uint i = 0; i < count; ++i)
  {
      resolved_depth += multisampledTexture.read(gid, i).r;
  }
  
  resolved_depth /= count;
  
  resolvedTexture.write(float4(resolved_depth, 0, 0, 0), gid);
}