RayTracingShader.Dispatch

Parameters

Description

Dispatches this RayTracingShader.

When a ray generation shader is executed, the GPU launches a 3D grid of threads. In HLSL, the values of width, height and depth can be retrieved using DispatchRaysDimensions() function. To retrieve the index of the ray generation shader invocation, DispatchRaysIndex() HLSL function can be used.

Width, height and depth must be above zero and width*height*depth <= 2^30.

When an optional Camera is specified as parameter, the built-in shader variables related to the Camera, Screen and Time are set up. Check Built-in shader variables for a complete list of these variables.

#include "UnityShaderVariables.cginc"

#pragma max_recursion_depth 1

// Input
RaytracingAccelerationStructure g_SceneAccelStruct;
float g_Zoom; //Mathf.Tan(Mathf.Deg2Rad * Camera.main.fieldOfView * 0.5f)

// Output
RWTexture2D<float4> g_Output;

struct RayPayload
{
    float4 color;
};

[shader("miss")]
void MainMissShader(inout RayPayload payload : SV_RayPayload)
{
    payload.color = float4(0, 0, 0, 1);
}

[shader("raygeneration")]
void MainRayGenShader()
{
    uint2 launchIndex = DispatchRaysIndex().xy;
    uint2 launchDim = DispatchRaysDimensions().xy;

    float2 frameCoord = float2(launchIndex.x, launchDim.y - launchIndex.y - 1) + float2(0.5, 0.5);

    float2 ndcCoords = frameCoord / float2(launchDim.x - 1, launchDim.y - 1);

    ndcCoords = ndcCoords * 2 - float2(1, 1);
    ndcCoords = ndcCoords * g_Zoom;

    float aspectRatio = (float)launchDim.x / (float)launchDim.y;

    float3 viewDirection = normalize(float3(ndcCoords.x * aspectRatio, ndcCoords.y, 1));

    // Rotate the ray from view space to world space.
    float3 rayDirection = normalize(mul((float3x3)unity_CameraToWorld, viewDirection));

    RayDesc ray;
    ray.Origin    = _WorldSpaceCameraPos;
    ray.Direction = rayDirection;
    ray.TMin      = 0.0f;
    ray.TMax      = 1000.0f;

    RayPayload payload;
    payload.color = float4(1, 1, 1, 1);

    uint missShaderIndex = 0;
    TraceRay(g_SceneAccelStruct, 0, 0xFF, 0, 1, missShaderIndex, ray, payload);

    g_Output[frameCoord] = payload.color;
}

This is a simple ray generation shader example where a ray direction is calculated based on the current 2D thread index returned by the DispatchRaysIndex() function. The output will contain a white color value if there is a ray/triangle intersection or a black color value if nothing is hit (MainMissShader is executed). In this example, unity_CameraToWorld built-in shader variable is used and in order for this value to be correctly set, a Camera has to be specified as argument for the Dispatch function.