VkAccelerationStructureBuildRangeInfoKHR

VkAccelerationStructureBuildRangeInfoKHR is defined as:

typedef struct VkAccelerationStructureBuildRangeInfoKHR {
    uint32_t primitiveCount;
    uint32_t primitiveOffset;
    uint32_t firstVertex;
    uint32_t transformOffset;
} VkAccelerationStructureBuildRangeInfoKHR;

• primitiveCount defines the number of primitives for a corresponding acceleration structure geometry.
• primitiveOffset defines an offset in bytes into the memory where primitive data is defined.
• firstVertex is the index of the first vertex to build from for triangle geometry.
• transformOffset defines an offset in bytes into the memory where a transform matrix is defined.

The primitive count and primitive offset are interpreted differently depending on the VkGeometryTypeKHR used:

• For geometries of type VK_GEOMETRY_TYPE_TRIANGLES_KHR, primitiveCount is the number of triangles to be built, where each triangle is treated as 3 vertices.
  • If the geometry uses indices, primitiveCount × 3 indices are consumed from VkAccelerationStructureGeometryTrianglesDataKHR::indexData, starting at an offset of primitiveOffset. The value of firstVertex is added to the index values before fetching vertices.
  • If the geometry does not use indices, primitiveCount × 3 vertices are consumed from VkAccelerationStructureGeometryTrianglesDataKHR::vertexData, starting at an offset of primitiveOffset + VkAccelerationStructureGeometryTrianglesDataKHR::vertexStride × firstVertex.
  • If VkAccelerationStructureGeometryTrianglesDataKHR::transformData is not NULL, a single VkTransformMatrixKHR structure is consumed from VkAccelerationStructureGeometryTrianglesDataKHR::transformData, at an offset of transformOffset. This matrix describes a transformation from the space in which the vertices for all triangles in this geometry are described to the space in which the acceleration structure is defined.
• For geometries of type VK_GEOMETRY_TYPE_AABBS_KHR, primitiveCount is the number of axis-aligned bounding boxes. primitiveCount VkAabbPositionsKHR structures are consumed from VkAccelerationStructureGeometryAabbsDataKHR::data, starting at an offset of primitiveOffset.
• For geometries of type VK_GEOMETRY_TYPE_SPHERES_NV, primitiveCount is the number of spheres to be built, where each sphere is treated as 1 vertex.
  • If the geometry uses indices, primitiveCount indices are consumed from VkAccelerationStructureGeometrySpheresDataNV::indexData, starting at an offset of primitiveOffset. The value of firstVertex is added to the index values before fetching vertices and radii.
  • If the geometry does not use indices, primitiveCount vertices and radii are consumed from VkAccelerationStructureGeometrySpheresDataNV::vertexData, starting at an offset of primitiveOffset + VkAccelerationStructureGeometrySpheresDataNV::vertexStride × firstVertex and VkAccelerationStructureGeometrySpheresDataNV::radiusData, starting at an offset of primitiveOffset + VkAccelerationStructureGeometrySpheresDataNV::radiusStride × firstVertex respectively.
• For geometries of type VK_GEOMETRY_TYPE_LINEAR_SWEPT_SPHERES_NV, primitiveCount is the number of LSS primitives to be built, where each LSS primitive is treated as 2 vertices.
  • If the geometry uses indices, primitiveCount × 2 indices are consumed from VkAccelerationStructureGeometryLinearSweptSpheresDataNV::indexData, starting at an offset of primitiveOffset. The value of firstVertex is added to the index values before fetching vertices and radii.
  • If the geometry does not use indices, primitiveCount × 2 vertices and radii are consumed from VkAccelerationStructureGeometryLinearSweptSpheresDataNV::vertexData, starting at an offset of primitiveOffset + VkAccelerationStructureGeometryLinearSweptSpheresDataNV::vertexStride × firstVertex and VkAccelerationStructureGeometryLinearSweptSpheresDataNV::radiusData, starting at an offset of primitiveOffset + VkAccelerationStructureGeometryLinearSweptSpheresDataNV::radiusStride × firstVertex respectively.
• For geometries of type VK_GEOMETRY_TYPE_INSTANCES_KHR, primitiveCount is the number of acceleration structures. primitiveCount VkAccelerationStructureInstanceKHR or VkAccelerationStructureMotionInstanceNV structures are consumed from VkAccelerationStructureGeometryInstancesDataKHR::data, starting at an offset of primitiveOffset.

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