Bombaleila/Library/PackageCache/com.unity.render-pipelines.core@04ab0eefa0c3/Documentation~/UnifiedRayTracing/shader-code-reference.md

Unified ray tracing shader code reference

This section presents the different functions and structs provided by the API for tracing rays in a shader.

All types are defined inside the UnifiedRT namespace. In your code, you need to prefix them with UnifiedRT::. Alternatively, you can add using namespace UnifiedRT; after your TraceRayAndQueryHit.hlsl include statement.

function TraceRayClosestHit

Hit TraceRayClosestHit(DispatchInfo dispatchInfo, RayTracingAccelStruct accelStruct, uint instanceMask, Ray ray, uint rayFlags)

Searches for intersections between a ray and an acceleration structure. It returns hit information about the closest triangle encountered along the ray.

Parameters

Type	Name	Description
DispatchInfo	dispatchInfo	The dispatch info. Must be the value that is passed by RayGenExecute.
RayTracingAccelStruct	accelStruct	The acceleration structure to test the ray against.
uint	instanceMask	The lower 8 bits of this mask are used to include geometry instances based on the instance mask that was set in MeshInstanceDesc for each instance.
Ray	ray	Describes the ray segment that is intersected against the acceleration structure.
uint	rayFlags	Flags that filter out the triangles that participate in the intersection test. Can be one of the following: kRayFlagNone kRayFlagCullBackFacingTriangles kRayFlagCullFrontFacingTriangles

Returns

Hit containing geometry information about the hit triangle. When no primitive has intersected with the ray, hit.IsValid() returns false.

function TraceRayAnyHit

bool TraceRayAnyHit(DispatchInfo dispatchInfo, RayTracingAccelStruct accelStruct, uint instanceMask, Ray ray, uint rayFlags)

Searches for any intersection between a ray and an acceleration structure. The search ends as soon as a valid triangle hit is found. This function can typically be used to trace shadow rays or perform occlusion queries.

Parameters

Type	Name	Description
DispatchInfo	dispatchInfo	The dispatch info. Must be the value that is passed by RayGenExecute.
RayTracingAccelStruct	accelStruct	The acceleration structure to test the ray against.
uint	instanceMask	The lower 8 bits of this mask are used to include geometry instances based on the instance mask that was set in MeshInstanceDesc for each instance.
Ray	ray	Describes the ray segment that is intersected against the acceleration structure.
uint	rayFlags	Flags that filter out the triangles that participate in the intersection test. Can be one of the following: kRayFlagNone kRayFlagCullBackFacingTriangles kRayFlagCullFrontFacingTriangles

Returns

A boolean that is true if any primitive was hit by the ray.

struct Ray

Describes a ray. The tMin and tMax fields define the segment of the ray to be tested against the acceleration structures's primitives. Mathematically, the ray consists of all the points defined as P = ray.origin + t * ray.direction, where ray.tMin ≤ t ≤ ray.tMax.

Fields

Type	Name	Description
float3	origin	The ray's origin.
float3	direction	The ray's direction.
float	tMin	The ray's starting point.
float	tMax	The ray's endpoint.

struct DispatchInfo

Provides information about the current thread that is invoked.

Fields

Type	Name	Description
uint3	dispatchThreadID	Same semantic as SV_DispatchThreadID.
uint	localThreadIndex	Same semantic as SV_GroupIndex.
uint3	dispatchDimensionsInThreads	Total numbers of threads dispatched in the X, Y, and Z workgrid directions.
uint	globalThreadIndex	Global thread index that is unique within the workgrid.

struct Hit

Describes a Hit.

Fields

Type	Name	Description
uint	instanceID	Matches the instanceID supplied from C# in MeshInstanceDesc.instanceID.
uint	primitiveIndex	Index of the hit triangle in its source Mesh.
float2	uvBarycentrics	Barycentric coordinates of the hit triangle.
float	hitDistance	Defines the hit position: hitPos = ray.origin + ray.direction * hit.hitDistance.
bool	isFrontFace	Indicates whether the hit triangle is front-facing or back-facing.

Methods

bool IsValid();

Returns true when a hit has been found. When a hit is invalid hit.instanceID is equal to ~0 and the other fields are undefined.