C Specification
The VkClusterAccelerationStructureBuildTriangleClusterTemplateInfoNV structure is defined as:
// Provided by VK_NV_cluster_acceleration_structure
typedef struct VkClusterAccelerationStructureBuildTriangleClusterTemplateInfoNV {
    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;Members
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clusterIDis a user specified identifier assigned to this cluster template.
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clusterFlagsis a bitmask of VkClusterAccelerationStructureClusterFlagBitsNV values describing flags how the cluster template should be built.
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triangleCountis the number of triangles in this cluster.
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vertexCountis the number of unique vertices in this cluster.
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positionTruncateBitCountis 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.
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indexTypeis a single VkClusterAccelerationStructureIndexFormatFlagBitsNV value specifying the index type inindexBuffer.
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opacityMicromapIndexTypeis a single VkClusterAccelerationStructureIndexFormatFlagBitsNV value specifying the index type inopacityMicromapIndexBuffer.
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baseGeometryIndexAndGeometryFlagsis a VkClusterAccelerationStructureGeometryIndexAndGeometryFlagsNV value specifying the base geometry index and flags for all triangles in the cluster template.
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indexBufferStrideis the stride in bytes inindexBuffer.
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vertexBufferStrideis the stride in bytes invertexBuffer.
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geometryIndexAndFlagsBufferStrideis the stride in bytes ingeometryIndexAndFlagsBuffer.
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opacityMicromapIndexBufferStrideis the stride in bytes inopacityMicromapIndexBuffer.
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indexBuffercontains the indices of vertices in the cluster and is of typeindexType.
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vertexBufferis eitherNULLor specifies the vertex data of the triangles in the cluster template with format specified in VkClusterAccelerationStructureTriangleClusterInputNV::vertexFormat.
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geometryIndexAndFlagsBufferis eitherNULLor an address containing strided VkClusterAccelerationStructureGeometryIndexAndGeometryFlagsNV values specifying the geometry index and flag for every triangle in the cluster.
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opacityMicromapArrayis eitherNULLor specifies the address of a valid opacity micromap array to reference from the cluster acceleration structure. If it isNULL, then opacity micromaps will be disabled for this cluster acceleration structure.
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opacityMicromapIndexBufferis eitherNULLor specifies the address of a strided array with size equal to the number of triangles or indices into the opacity micromap array.
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instantiationBoundingBoxLimitis eitherNULLor 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.
Description
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:
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triangleCount,vertexCount,positionTruncateBitCount,indexTypeandopacityMicromapIndexTypeoccupy the same memory as if a singleuint32_twas specified in their place- 
triangleCountoccupies the 9 least significant bits of that memory
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vertexCountoccupies the next 9 least significant bits of that memory
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positionTruncateBitCountoccupies the next 6 least significant bits of that memory
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indexTypeoccupies the next 4 least significant bits of that memory
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opacityMicromapIndexTypeoccupies the 4 most significant bits of that memory
 
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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.
Document Notes
For more information, see the Vulkan Specification
This page is extracted from the Vulkan Specification. Fixes and changes should be made to the Specification, not directly.