56 lines
2.5 KiB
Markdown
56 lines
2.5 KiB
Markdown
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# Execute your ray tracing code
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This section assumes you have [a shader](create-shader.md) containing your ray tracing logic and an [acceleration structure](create-acceleration-structure.md) representing the geometry that the rays will intersect.
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To execute your ray tracing shader on the GPU:
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1. Build the acceleration structure.
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2. Bind resources to the shader.
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3. Dispatch the shader.
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## Build the acceleration structure
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You must build the acceleration structure after you create it and every time you modify it. For example:
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```C#
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IRayTracingAccelStruct rtAccelStruct = /* your acceleration structure */;
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var cmd = new CommandBuffer();
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// A scratch buffer is required to build the acceleration structure, this helper function allocates one with the required size.
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GraphicsBuffer buildScratchBuffer = RayTracingHelper.CreateScratchBufferForBuild(rtAccelStruct);
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// Build the ray tracing acceleration structure
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rtAccelStruct.Build(cmd, buildScratchBuffer);
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```
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## Bind resources to the shader
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You must bind the acceleration structure and any additional GPU resources declared in your shader, such as constants, buffers, and textures. For example:
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```C#
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IRayTracingShader rtShader = /* your shader */;
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// Bind the acceleration structure. It is declared in the shader as: UNIFIED_RT_DECLARE_ACCEL_STRUCT(_YourAccelStruct);
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rtShader.SetAccelerationStructure(cmd, "_YourAccelStruct", rtAccelStruct);
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// Bind the other GPU resources (constants/uniforms, buffers and textures)
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rtShader.SetIntParam(cmd, Shader.PropertyToID("_YourInteger"), 5);
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```
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## Dispatch the shader
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To make the GPU run your ray tracing shader, call the [`Dispatch`](xref:UnityEngine.Rendering.UnifiedRayTracing.IRayTracingShader.Dispatch(UnityEngine.Rendering.CommandBuffer,UnityEngine.GraphicsBuffer,System.UInt32,System.UInt32,System.UInt32)) method. For example:
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```C#
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const int threadCountX = 256, threadCountY = 256, threadCountZ = 1;
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// A scratch buffer is required to trace rays, this helper function allocates one with the required size.
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GraphicsBuffer traceScratchBuffer = RayTracingHelper.CreateScratchBufferForTrace(rtShader, threadCountX, threadCountY, threadCountZ);
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// Dispatch rays. Workgrid dimensions are supplied in threads, not workgroups
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rtShader.Dispatch(cmd, traceScratchBuffer, threadCountX, threadCountY, threadCountZ);
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// Execute the command buffer to effectively run all the previously registered commands.
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Graphics.ExecuteCommandBuffer(cmd);
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```
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**Note:** If its size satisfies the requirements for both operations, you can use the same scratch buffer for both the build and trace steps.
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