Ray Tracing

Zenith.NET Ray Tracing uses bottom-level and top-level acceleration structures with inline Slang RayQuery operations.

Check Support

Check context.Capabilities.RayTracingSupported before creating Ray Tracing resources.

Build a BLAS

A bottom-level acceleration structure (BLAS) contains triangle or axis-aligned bounding-box geometry. Set Geometries and BuildFlags in its description, then record the build:

BottomLevelAccelerationStructureDesc desc = new()
{
    Geometries = geometries,
    BuildFlags = AccelerationStructureBuildFlags.PreferFastTrace
};

BottomLevelAccelerationStructure resource = commandBuffer.BuildAccelerationStructure(desc);

Use RayTracingGeometry.Aabbs instead when the geometry is represented by bounding boxes.

Build a TLAS

The top-level acceleration structure (TLAS) contains instances of existing BLAS objects. Set Instances and BuildFlags in its description, then record the build:

TopLevelAccelerationStructureDesc desc = new()
{
    Instances = instances,
    BuildFlags = AccelerationStructureBuildFlags.PreferFastTrace
};

TopLevelAccelerationStructure resource = commandBuffer.BuildAccelerationStructure(desc);

Submit the build before tracing against the TLAS. Work submitted to the same queue remains ordered; when tracing on another queue, pass the build submission's TimelineValue to the tracing submission.

Keep every referenced BLAS alive while the TLAS is in use.

Update an Acceleration Structure

Set AllowUpdate on the initial build and every later in-place update, and pass the updated description to UpdateAccelerationStructure.

Choose PreferFastTrace, PreferFastBuild, or MinimizeMemory according to how the structure is used.

Trace Rays in Slang

Store the TLAS handle in constant data and declare the matching field as DescriptorHandle<RaytracingAccelerationStructure> in Slang.

For triangle geometry, initialize a RayQuery, trace it, and inspect the committed result:

RayDesc ray;
ray.Origin = origin;
ray.Direction = direction;
ray.TMin = 0.001;
ray.TMax = 100000.0;

RayQuery<RAY_FLAG_NONE> query;
query.TraceRayInline(*constants.Resource, RAY_FLAG_NONE, 0xFF, ray);

while (query.Proceed())
{
}

bool hit = query.CommittedStatus() != COMMITTED_NOTHING;

For procedural AABB geometry, handle each CANDIDATE_PROCEDURAL_PRIMITIVE during Proceed() and call CommitProceduralPrimitiveHit for an accepted intersection.