Execute your ray tracing code

This section assumes you have a shader containing your ray tracing logic and an acceleration structure representing the geometry that the rays will intersect.

To execute your ray tracing shader on the GPU:

  1. Build the acceleration structure.
  2. Bind resources to the shader.
  3. Dispatch the shader.

Build the acceleration structure

You must build the acceleration structure after you create it and every time you modify it. For example:

IRayTracingAccelStruct rtAccelStruct = /* your acceleration structure */;
var cmd = new CommandBuffer();

// A scratch buffer is required to build the acceleration structure, this helper function allocates one with the required size.
GraphicsBuffer buildScratchBuffer = RayTracingHelper.CreateScratchBufferForBuild(rtAccelStruct);

// Build the ray tracing acceleration structure
rtAccelStruct.Build(cmd, buildScratchBuffer);

Bind resources to the shader

You must bind the acceleration structure and any additional GPU resources declared in your shader, such as constants, buffers, and textures. For example:

IRayTracingShader rtShader = /* your shader */;

// Bind the acceleration structure. It is declared in the shader as: UNIFIED_RT_DECLARE_ACCEL_STRUCT(_YourAccelStruct);
rtShader.SetAccelerationStructure(cmd, "_YourAccelStruct", rtAccelStruct);

// Bind the other GPU resources (constants/uniforms, buffers and textures)
rtShader.SetIntParam(cmd, Shader.PropertyToID("_YourInteger"), 5);

Dispatch the shader

To make the GPU run your ray tracing shader, call the Dispatch method. For example:

const int threadCountX = 256, threadCountY = 256, threadCountZ = 1;

// A scratch buffer is required to trace rays, this helper function allocates one with the required size.
GraphicsBuffer traceScratchBuffer = RayTracingHelper.CreateScratchBufferForTrace(rtShader, threadCountX, threadCountY, threadCountZ);

// Dispatch rays. Workgrid dimensions are supplied in threads, not workgroups
rtShader.Dispatch(cmd, traceScratchBuffer, threadCountX, threadCountY, threadCountZ);

// Execute the command buffer to effectively run all the previously registered commands.
Graphics.ExecuteCommandBuffer(cmd);

Note: If its size satisfies the requirements for both operations, you can use the same scratch buffer for both the build and trace steps.