D3D12_RAYTRACING_INSTANCE_DESC structure (d3d12.h)

Describes an instance of a raytracing acceleration structure used in GPU memory during the acceleration structure build process.

Syntax

typedef struct D3D12_RAYTRACING_INSTANCE_DESC {
  FLOAT                     Transform[3][4];
  UINT                      InstanceID : 24;
  UINT                      InstanceMask : 8;
  UINT                      InstanceContributionToHitGroupIndex : 24;
  UINT                      Flags : 8;
  D3D12_GPU_VIRTUAL_ADDRESS AccelerationStructure;
} D3D12_RAYTRACING_INSTANCE_DESC;

Members

Transform[3]

Type: FLOAT [3][4]

A 3x4 transform matrix in row-major layout representing the instance-to-world transformation. Implementations transform rays, as opposed to transforming all of the geometry or AABBs.

Note

The layout of Transform is a transpose of how affine matrices are typically stored in memory. Instead of four 3-vectors, Transform is laid out as three 4-vectors.

InstanceID

Type: UINT : 24

An arbitrary 24-bit value that can be accessed using the InstanceID intrinsic function in supported shader types.

InstanceMask

Type: UINT : 8

An 8-bit mask assigned to the instance, which can be used to include/reject groups of instances on a per-ray basis. If the value is zero, then the instance will never be included, so typically this should be set to some non-zero value. For more information see, the InstanceInclusionMask parameter to the TraceRay function.

InstanceContributionToHitGroupIndex

Type: UINT : 24

An arbitrary 24-bit value representing per-instance contribution to add into shader table indexing to select the hit group to use.

Flags

Type: UINT : 8

An 8-bit mask representing flags from D3D12_RAYTRACING_INSTANCE_FLAGS to apply to the instance.

AccelerationStructure

Type: D3D12_GPU_VIRTUAL_ADDRESS

Address of the bottom-level acceleration structure that is being instanced. The address must be aligned to 256 bytes, defined as D3D12_RAYTRACING_ACCELERATION_STRUCTURE_BYTE_ALIGNMENT. Any existing acceleration structure passed in here would already have been required to be placed with such alignment.

The memory pointed to must be in state D3D12_RESOURCE_STATE_RAYTRACING_ACCELERATION_STRUCTURE.

Remarks

This C++ struct definition is useful if you're generating instance data on the CPU first, then uploading to the GPU. But your application is also free to generate instance descriptions directly into GPU memory (from compute shaders, for instance) following the same layout.

Requirements

Requirement	Value
Header	d3d12.h