VkClusterAccelerationStructureBuildTriangleClusterTemplateInfoNV

The VkClusterAccelerationStructureBuildTriangleClusterTemplateInfoNV structure is defined as:

typedef struct VkClusterAccelerationStructureBuildTriangleClusterTemplateInfoNV {
    // The bitfields in this structure are non-normative since bitfield ordering is implementation-defined in C. The specification defines the normative layout.;
    uint32_t clusterID;
    VkClusterAccelerationStructureClusterFlagsNV clusterFlags;
    uint32_t triangleCount:9;
    uint32_t vertexCount:9;
    uint32_t positionTruncateBitCount:6;
    uint32_t indexType:4;
    uint32_t opacityMicromapIndexType:4;
    VkClusterAccelerationStructureGeometryIndexAndGeometryFlagsNV baseGeometryIndexAndGeometryFlags;
    uint16_t indexBufferStride;
    uint16_t vertexBufferStride;
    uint16_t geometryIndexAndFlagsBufferStride;
    uint16_t opacityMicromapIndexBufferStride;
    VkDeviceAddress indexBuffer;
    VkDeviceAddress vertexBuffer;
    VkDeviceAddress geometryIndexAndFlagsBuffer;
    VkDeviceAddress opacityMicromapArray;
    VkDeviceAddress opacityMicromapIndexBuffer;
    VkDeviceAddress instantiationBoundingBoxLimit;
} VkClusterAccelerationStructureBuildTriangleClusterTemplateInfoNV;

• clusterID is a user specified identifier assigned to this cluster template.
• clusterFlags is a bitmask of VkClusterAccelerationStructureClusterFlagBitsNV values describing flags how the cluster template should be built.
• triangleCount is the number of triangles in this cluster.
• vertexCount is the number of unique vertices in this cluster.
• positionTruncateBitCount is the number of bits starting at the lowest bit (i.e. the LSBs of the mantissa), of each vertex position that will be truncated to zero to improve floating-point compression.
• indexType is a single VkClusterAccelerationStructureIndexFormatFlagBitsNV value specifying the index type in indexBuffer.
• opacityMicromapIndexType is a single VkClusterAccelerationStructureIndexFormatFlagBitsNV value specifying the index type in opacityMicromapIndexBuffer.
• baseGeometryIndexAndGeometryFlags is a VkClusterAccelerationStructureGeometryIndexAndGeometryFlagsNV value specifying the base geometry index and flags for all triangles in the cluster template.
• indexBufferStride is the stride in bytes in indexBuffer.
• vertexBufferStride is the stride in bytes in vertexBuffer.
• geometryIndexAndFlagsBufferStride is the stride in bytes in geometryIndexAndFlagsBuffer.
• opacityMicromapIndexBufferStride is the stride in bytes in opacityMicromapIndexBuffer.
• indexBuffer contains the indices of vertices in the cluster and is of type indexType.
• vertexBuffer is either NULL or specifies the vertex data of the triangles in the cluster template with format specified in VkClusterAccelerationStructureTriangleClusterInputNV::vertexFormat.
• geometryIndexAndFlagsBuffer is either NULL or an address containing strided VkClusterAccelerationStructureGeometryIndexAndGeometryFlagsNV values specifying the geometry index and flag for every triangle in the cluster.
• opacityMicromapArray is either NULL or specifies the address of a valid opacity micromap array to reference from the cluster acceleration structure. If it is NULL, then opacity micromaps will be disabled for this cluster acceleration structure.
• opacityMicromapIndexBuffer is either NULL or specifies the address of a strided array with size equal to the number of triangles or indices into the opacity micromap array.
• instantiationBoundingBoxLimit is either NULL or specifies the address of a bounding box within which all instantiated clusters must lie. The bounding box is specified by six 32-bit floating-point values in the order MinX, MinY, MinZ, MaxX, MaxY, MaxZ.

The C language specification does not define the ordering of bit-fields, but in practice, this structure produces the correct layout with existing compilers. The intended bit pattern is the following:

• triangleCount, vertexCount, positionTruncateBitCount, indexType and opacityMicromapIndexType occupy the same memory as if a single uint32_t was specified in their place
  • triangleCount occupies the 9 least significant bits of that memory
  • vertexCount occupies the next 9 least significant bits of that memory
  • positionTruncateBitCount occupies the next 6 least significant bits of that memory
  • indexType occupies the next 4 least significant bits of that memory
  • opacityMicromapIndexType occupies the 4 most significant bits of that memory

If a compiler produces code that diverges from that pattern, applications must employ another method to set values according to the correct bit pattern.

Cluster templates cannot be directly used to build bottom level acceleration structures, instead, they must be instantiated into CLAS objects.