"Clip" function fails on raytracing passes with "Opcode Discard not valid in shader model lib_6_3"

Unity Engine
,
1

I am trying to use the clip function in raytracing passes (not via shadergraph but with regular code) but I get “Opcode Discard not valid in shader model lib_6_3(anyhint)” message(there are variants for closehit too, the discard code works with regular raster passes. It gives this error on raytracing.

If clipping/discard is not supported on raytracing shaders, is there a way to do clip other than using this?

2

clip and discard are rasterization instruction available in pixel shaders only.

You can get a similar functionality in ray tracing using anyhit shaders where alpha can come from a texture. Anyhit shaders are usually used for alpha tested / cutout Materials. If you use RayTracingAccelerationStructure.AddInstance functions you’ll need to specify just RayTracingSubMeshFlags.Enable - this will enable anyhit shaders.

Some example:

_Cutoff and _MainTex are shader properties.

[shader(“anyhit”)]
void AnyHitMain(inout RayPayload payload : SV_RayPayload, AttributeData attribs : SV_IntersectionAttributes)
{
uint3 triangleIndices = UnityRayTracingFetchTriangleIndices(PrimitiveIndex());
Vertex v0, v1, v2;
v0 = FetchVertex(triangleIndices.x);
v1 = FetchVertex(triangleIndices.y);
v2 = FetchVertex(triangleIndices.z);
float3 barycentricCoords = float3(1.0 - attribs.barycentrics.x - attribs.barycentrics.y, attribs.barycentrics.x, attribs.barycentrics.y);
Vertex v = InterpolateVertices(v0, v1, v2, barycentricCoords);
float alpha = _MainTex.SampleLevel(sampler__MainTex, _MainTex_ST.xy * v.uv + _MainTex_ST.zw, 0).w;
if (alpha < _Cutoff)
IgnoreHit();
}