Scene Color Sampling in AfterPostProcess Custom Pass

Overview

When using AfterPostProcess injection point with FullScreenShaderGraph that samples scene color, you might need to handle concurrent read/write operations on the color buffer. This page explains the recommended implementation for proper scene color sampling.

Technical Details

At the AfterPostProcess injection point, the color buffer serves as both the render target and the source for scene color sampling. To ensure correct sampling, you can implement a solution using a temporary buffer.

Implementation Example

Here's an example of how to properly sample scene color in an AfterPostProcess Custom Pass:

class SceneColorSamplingPass : CustomPass
{
    RTHandle m_TempColorBuffer;

    protected override void Setup(ScriptableRenderContext renderContext, CommandBuffer cmd)
    {
        // Create temporary buffer with the same properties as camera color buffer
        m_TempColorBuffer = RTHandles.Alloc(
            Vector2.one, TextureXR.slices, dimension: TextureXR.dimension,
            colorFormat: GetColorBufferFormat(),
            name: "SceneColorSamplingBuffer"
        );
    }

    protected override void Execute(CustomPassContext ctx)
    {
        // Copy the scene color to temporary buffer
        ctx.cmd.CopyTexture(ctx.cameraColorBuffer, m_TempColorBuffer);
        
        // Bind temporary buffer for sampling
        ctx.cmd.SetGlobalTexture("_AfterPostProcessColorBuffer", m_TempColorBuffer);
        
        // Your custom pass rendering code here
        // ...
    }

    protected override void Cleanup()
    {
        // Release the temporary buffer
        RTHandles.Release(m_TempColorBuffer);
    }
}

Performance Considerations

When implementing this solution, keep in mind:

  • This approach allocates an additional full-resolution color buffer
  • Only implement this solution when you need to sample the scene color
  • Consider using a different injection point if your use case allows it

See Also