RayTracingAccelerationStructure.CullInstances

Parameters

Returns

RayTracingInstanceCullingResults Culling results.

Description

Populates the acceleration structure with ray tracing instances associated with Renderers in the Scene using various filtering and culling parameters.

The previous content of the acceleration structure can optionally be cleared by using RayTracingAccelerationStructure.ClearInstances. After calling this function, additional ray tracing instances can be added to the acceleration structure using RayTracingAccelerationStructure.AddInstance functions.

If RayTracingInstanceCullingConfig.instanceTests array is empty then this function doesn't have any effect.

Note that building the acceleration structure on the GPU has to be triggered by calling RayTracingAccelerationStructure.Build or CommandBuffer.BuildRayTracingAccelerationStructure.

Additional resources: RayTracingShader.

using System.Collections;
using System.Collections.Generic;
using UnityEngine;
using UnityEngine.Rendering;
using UnityEngine.Experimental.Rendering;

// This script can be attached to a Camera.
public class CullInstancesExample : MonoBehaviour
{
    // A RayTracingShader is defined in a .raytrace file.
    public RayTracingShader rayTracingShader = null;

    public bool enableRayTracedReflections = true;
    public bool enableRayTracedShadows = true;

    private int cameraWidth = 0;
    private int cameraHeight = 0;

    private RenderTexture rayTracingOutput = null;
    private RayTracingAccelerationStructure rayTracingAccelStruct = null;

    void Start()
    {
        if (SystemInfo.supportsRayTracing == false)
        {
            Debug.Log("The system doesn't support Ray Tracing.");
            return;
        }

        RayTracingAccelerationStructure.RASSettings accelStructSetting = new RayTracingAccelerationStructure.RASSettings(RayTracingAccelerationStructure.ManagementMode.Manual, RayTracingAccelerationStructure.RayTracingModeMask.Everything, -1);
        rayTracingAccelStruct = new RayTracingAccelerationStructure(accelStructSetting);
    }

    void OnDisable()
    {
        if (rayTracingAccelStruct != null)
        {
            rayTracingAccelStruct.Release();
            rayTracingAccelStruct = null;
        }

        if (rayTracingOutput)
        {
            rayTracingOutput.Release();
            rayTracingOutput = null;
        }

        cameraWidth = 0;
        cameraHeight = 0;
    }

    void OnRenderImage(RenderTexture src, RenderTexture dest)
    {
        if (SystemInfo.supportsRayTracing == false || rayTracingShader == null)
            return;

        if (cameraWidth != Camera.main.pixelWidth || cameraHeight != Camera.main.pixelHeight)
        {
            if (rayTracingOutput)
                rayTracingOutput.Release();

            rayTracingOutput = new RenderTexture(Camera.main.pixelWidth, Camera.main.pixelHeight, 0, RenderTextureFormat.ARGBHalf);
            rayTracingOutput.enableRandomWrite = true;
            rayTracingOutput.Create();

            cameraWidth = Camera.main.pixelWidth;
            cameraHeight = Camera.main.pixelHeight;
        }

        RayTracingInstanceCullingConfig cullingConfig = new RayTracingInstanceCullingConfig();

        cullingConfig.flags = RayTracingInstanceCullingFlags.EnableLODCulling | RayTracingInstanceCullingFlags.EnableSphereCulling;

        // Configure sphere culling.
        cullingConfig.sphereCenter = Camera.main.transform.position;
        cullingConfig.sphereRadius = 100.0f;

        // Configure LOD masking.
        cullingConfig.lodParameters.fieldOfView = Camera.main.fieldOfView;
        cullingConfig.lodParameters.cameraPosition = Camera.main.transform.position;
        cullingConfig.lodParameters.cameraPixelHeight = Camera.main.pixelHeight;
        cullingConfig.lodParameters.orthoSize = 0;
        cullingConfig.lodParameters.isOrthographic = false;

        // Disable anyhit shaders for opaque geometries for best ray tracing performance.
        cullingConfig.subMeshFlagsConfig.opaqueMaterials = RayTracingSubMeshFlags.Enabled | RayTracingSubMeshFlags.ClosestHitOnly;

        // Disable transparent geometries.
        cullingConfig.subMeshFlagsConfig.transparentMaterials = RayTracingSubMeshFlags.Disabled;

        // Enable anyhit shaders for alpha-tested / cutout geometries.
        cullingConfig.subMeshFlagsConfig.alphaTestedMaterials = RayTracingSubMeshFlags.Enabled;

        // Configure which triangles are double sided. For best ray tracing performance, triangle culling should be disabled.
        cullingConfig.triangleCullingConfig.checkDoubleSidedGIMaterial = true;
        cullingConfig.triangleCullingConfig.frontTriangleCounterClockwise = false;
        cullingConfig.triangleCullingConfig.optionalDoubleSidedShaderKeywords = new string[1];
        cullingConfig.triangleCullingConfig.optionalDoubleSidedShaderKeywords[0] = "_DOUBLESIDED_ON";
        cullingConfig.triangleCullingConfig.forceDoubleSided = false;

        // Configure Material types. Render queue intervals can also be used here.
        cullingConfig.alphaTestedMaterialConfig.optionalShaderKeywords = new string[1];
        cullingConfig.alphaTestedMaterialConfig.optionalShaderKeywords[0] = "_ALPHATEST_ON";

        cullingConfig.transparentMaterialConfig.optionalShaderKeywords = new string[1];
        cullingConfig.transparentMaterialConfig.optionalShaderKeywords[0] = "_SURFACE_TYPE_TRANSPARENT";

        // Configure a Material test. Allow only Shaders that have a mandatory Shader Tag.
        cullingConfig.materialTest.requiredShaderTags = new RayTracingInstanceCullingShaderTagConfig[1];
        cullingConfig.materialTest.requiredShaderTags[0].tagId = new ShaderTagId("RenderPipeline");
        cullingConfig.materialTest.requiredShaderTags[0].tagValueId = new ShaderTagId("MyAwesomeRP");

        List<RayTracingInstanceCullingTest> instanceTests = new List<RayTracingInstanceCullingTest>();

        // Configure instance tests. There can be one instance test for each ray tracing effect for example.
        // The purpose of instance tests is to use different settings (layer, material types) per ray tracing effect.
        // Use InstanceInclusionMask argument of TraceRay HLSL function to mask different instance types.

        if (enableRayTracedReflections)
        {
            RayTracingInstanceCullingTest instanceTest = new RayTracingInstanceCullingTest();
            instanceTest.allowTransparentMaterials = false;
            instanceTest.allowOpaqueMaterials = true;
            instanceTest.allowAlphaTestedMaterials = true;
            instanceTest.layerMask = -1;
            instanceTest.shadowCastingModeMask = (1 << (int)ShadowCastingMode.Off) | (1 << (int)ShadowCastingMode.On) | (1 << (int)ShadowCastingMode.TwoSided);
            instanceTest.instanceMask = 1 << 0;

            instanceTests.Add(instanceTest);
        }

        if (enableRayTracedShadows)
        {
            RayTracingInstanceCullingTest instanceTest = new RayTracingInstanceCullingTest();
            instanceTest.allowTransparentMaterials = false;
            instanceTest.allowOpaqueMaterials = true;
            instanceTest.allowAlphaTestedMaterials = true;
            instanceTest.layerMask = -1;
            instanceTest.shadowCastingModeMask = (1 << (int)ShadowCastingMode.On) | (1 << (int)ShadowCastingMode.TwoSided);
            instanceTest.instanceMask = 1 << 1;

            instanceTests.Add(instanceTest);
        }

        cullingConfig.instanceTests = instanceTests.ToArray();

        rayTracingAccelStruct.ClearInstances();
        rayTracingAccelStruct.CullInstances(ref cullingConfig);

        // Additional ray tracing instances can be added manually using RayTracingAccelerationStructure.AddInstance function.
        // rayTracingAccelStruct.AddInstance(...);

        rayTracingAccelStruct.Build(Camera.main.transform.position);

        // Use Shader Pass "Test" in surface (material) shaders.
        rayTracingShader.SetShaderPass("Test");

        rayTracingShader.SetAccelerationStructure("g_AccelStruct", rayTracingAccelStruct);
        rayTracingShader.SetTexture("g_Output", rayTracingOutput);

        rayTracingShader.Dispatch("MainRayGenShader", rayTracingOutput.width, rayTracingOutput.height, 1);

        Graphics.Blit(rayTracingOutput, dest);
    }
}

This is an example of how to create, populate and build an acceleration structure. The content of the acceleration structure is specified by configuring culling and filtering parameters that are passed to the CullInstances function.