VkAccelerationStructureBuildGeometryInfoKHR

The VkAccelerationStructureBuildGeometryInfoKHR structure is defined as:

typedef struct VkAccelerationStructureBuildGeometryInfoKHR {
    VkStructureType sType;
    const void* pNext;
    VkAccelerationStructureTypeKHR type;
    VkBuildAccelerationStructureFlagsKHR flags;
    VkBuildAccelerationStructureModeKHR mode;
    VkAccelerationStructureKHR srcAccelerationStructure;
    VkAccelerationStructureKHR dstAccelerationStructure;
    uint32_t geometryCount;
    const VkAccelerationStructureGeometryKHR* pGeometries;
    const VkAccelerationStructureGeometryKHR* const* ppGeometries;
    VkDeviceOrHostAddressKHR scratchData;
} VkAccelerationStructureBuildGeometryInfoKHR;

• sType is a VkStructureType value identifying this structure.
• pNext is NULL or a pointer to a structure extending this structure.
• type is a VkAccelerationStructureTypeKHR value specifying the type of acceleration structure being built.
• flags is a bitmask of VkBuildAccelerationStructureFlagBitsKHR specifying additional parameters of the acceleration structure.
• mode is a VkBuildAccelerationStructureModeKHR value specifying the type of operation to perform.
• srcAccelerationStructure is a pointer to an existing acceleration structure that is to be used to update the dstAccelerationStructure acceleration structure when mode is VK_BUILD_ACCELERATION_STRUCTURE_MODE_UPDATE_KHR.
• dstAccelerationStructure is a pointer to the target acceleration structure for the build.
• geometryCount specifies the number of geometries that will be built into dstAccelerationStructure.
• pGeometries is a pointer to an array of VkAccelerationStructureGeometryKHR structures.
• ppGeometries is a pointer to an array of pointers to VkAccelerationStructureGeometryKHR structures.
• scratchData is the device or host address to memory that will be used as scratch memory for the build.

Only one of pGeometries or ppGeometries can be a valid pointer, the other must be NULL. Each element of the non-NULL array describes the data used to build each acceleration structure geometry.

The index of each element of the pGeometries or ppGeometries members of VkAccelerationStructureBuildGeometryInfoKHR is used as the geometry index during ray traversal. The geometry index is available in ray shaders via the RayGeometryIndexKHR built-in, and is used to determine hit and intersection shaders executed during traversal. The geometry index is available to ray queries via the OpRayQueryGetIntersectionGeometryIndexKHR instruction.

Setting VK_BUILD_ACCELERATION_STRUCTURE_MOTION_BIT_NV in flags indicates that this build is a motion top level acceleration structure. A motion top level uses instances of format VkAccelerationStructureMotionInstanceNV if VkAccelerationStructureGeometryInstancesDataKHR::arrayOfPointers is VK_FALSE.

If VkAccelerationStructureGeometryInstancesDataKHR::arrayOfPointers is VK_TRUE, the pointer for each element of the array of instance pointers consists of 4 bits of VkAccelerationStructureMotionInstanceTypeNV in the low 4 bits of the pointer identifying the type of structure at the pointer. The device address accessed is the value in the array with the low 4 bits set to zero. The structure at the pointer is one of VkAccelerationStructureInstanceKHR, VkAccelerationStructureMatrixMotionInstanceNV or VkAccelerationStructureSRTMotionInstanceNV, depending on the type value encoded in the low 4 bits.

A top level acceleration structure with either motion instances or vertex motion in its instances must set VK_BUILD_ACCELERATION_STRUCTURE_MOTION_BIT_NV in flags.

Members srcAccelerationStructure and dstAccelerationStructuremay be the same or different for an update operation (when mode is VK_BUILD_ACCELERATION_STRUCTURE_MODE_UPDATE_KHR). If they are the same, the update happens in-place. Otherwise, the target acceleration structure is updated and the source is not modified.