Rasagar/Library/PackageCache/com.unity.render-pipelines.universal/Documentation~/render-graph-compute-shader-input.md

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urp-render-graph-compute-shader-input

Create input data for a compute shader

When you run a compute shader in a render pass, you can allocate a buffer to provide input data for the compute shader.

Follow these steps:

1. Create a graphics buffer, then add a handle to it in your pass data. For example:

   // Declare an input buffer
   public GraphicsBuffer inputBuffer;
   
   // Add a handle to the input buffer in your pass data
   class PassData
   {
       ...
       public BufferHandle input;
   }
   
   // Create the buffer in the render pass constructor
   public ComputePass(ComputeShader computeShader)
   {
       // Create the input buffer as a structured buffer
       // Create the buffer with a length of 5 integers, so you can input 5 values.
       inputBuffer = new GraphicsBuffer(GraphicsBuffer.Target.Structured, 5, sizeof(int));
   }
   

2. Set the data in the buffer. For example:

   var inputValues = new List<int> { 1, 2, 3, 4, 5 };
   inputBuffer.SetData(inputValues);
   

3. Use the ImportBuffer render graph API to convert the buffer to a handle the render graph system can use, then set the BufferHandle field in the pass data. For example:

   BufferHandle inputHandleRG = renderGraph.ImportBuffer(inputBuffer);
   passData.input = inputHandleRG;
   

4. Use the UseBuffer method to set the buffer as a readable buffer in the render graph system. For example:

   builder.UseBuffer(passData.input, AccessFlags.Read);
   

5. In your SetRenderFunc method, use the SetComputeBufferParam API to attach the buffer to the compute shader. For example:

   // The first parameter is the compute shader
   // The second parameter is the function that uses the buffer
   // The third parameter is the RWStructuredBuffer input variable to attach the buffer to
   // The fourth parameter is the handle to the input buffer
   context.cmd.SetComputeBufferParam(passData.computeShader, passData.computeShader.FindKernel("Main"), "inputData", passData.input);
   

Example

For a full example, refer to the example called Compute in the Universal Render Pipeline (URP) package samples.

Additional resources

• Compute shaders
• Writing shaders