vkGetAccelerationStructureBuildSizesKHR

To get the build sizes for an acceleration structure, call:

void vkGetAccelerationStructureBuildSizesKHR(
    VkDevice                                            device,
    VkAccelerationStructureBuildTypeKHR                 buildType,
    const VkAccelerationStructureBuildGeometryInfoKHR*  pBuildInfo,
    const uint32_t*  pMaxPrimitiveCounts,
    VkAccelerationStructureBuildSizesInfoKHR*           pSizeInfo);

• device is the logical device that will be used for creating the acceleration structure.
• buildType defines whether host or device operations (or both) are being queried for.
• pBuildInfo is a pointer to a VkAccelerationStructureBuildGeometryInfoKHR structure describing parameters of a build operation.
• pMaxPrimitiveCounts is a pointer to an array of pBuildInfo→geometryCount uint32_t values defining the number of primitives built into each geometry.
• pSizeInfo is a pointer to a VkAccelerationStructureBuildSizesInfoKHR structure which returns the size required for an acceleration structure and the sizes required for the scratch buffers, given the build parameters.

The srcAccelerationStructure, dstAccelerationStructure, and mode members of pBuildInfo are ignored. Any VkDeviceOrHostAddressKHR or VkDeviceOrHostAddressConstKHR members of pBuildInfo are ignored by this command, except that the hostAddress member of VkAccelerationStructureGeometryTrianglesDataKHR::transformData will be examined to check if it is NULL.

An acceleration structure created with the accelerationStructureSize returned by this command supports any build or update with a VkAccelerationStructureBuildGeometryInfoKHR structure and array of VkAccelerationStructureBuildRangeInfoKHR structures subject to the following properties:

• The build command is a host build command, and buildType is VK_ACCELERATION_STRUCTURE_BUILD_TYPE_HOST_KHR or VK_ACCELERATION_STRUCTURE_BUILD_TYPE_HOST_OR_DEVICE_KHR
• The build command is a device build command, and buildType is VK_ACCELERATION_STRUCTURE_BUILD_TYPE_DEVICE_KHR or VK_ACCELERATION_STRUCTURE_BUILD_TYPE_HOST_OR_DEVICE_KHR
• For VkAccelerationStructureBuildGeometryInfoKHR:
  • Its type, and flags members are equal to pBuildInfo→type and pBuildInfo→flags, respectively.
  • geometryCount is less than or equal to pBuildInfo→geometryCount.
  • For each element of either pGeometries or ppGeometries at a given index, its geometryType member is equal to pBuildInfo→geometryType.
  • For each element of either pGeometries or ppGeometries at a given index, its flags member is equal to the corresponding member of the same element in pBuildInfo.
  • For each element of either pGeometries or ppGeometries at a given index, with a geometryType member equal to VK_GEOMETRY_TYPE_TRIANGLES_KHR, the vertexFormat and indexType members of geometry.triangles are equal to the corresponding members of the same element in pBuildInfo.
  • For each element of either pGeometries or ppGeometries at a given index, with a geometryType member equal to VK_GEOMETRY_TYPE_TRIANGLES_KHR, the maxVertex member of geometry.triangles is less than or equal to the corresponding member of the same element in pBuildInfo.
  • For each element of either pGeometries or ppGeometries at a given index, with a geometryType member equal to VK_GEOMETRY_TYPE_TRIANGLES_KHR, if the applicable address in the transformData member of geometry.triangles is not NULL, the corresponding transformData.hostAddress parameter in pBuildInfo is not NULL.
• For each VkAccelerationStructureBuildRangeInfoKHR corresponding to the VkAccelerationStructureBuildGeometryInfoKHR:
  • Its primitiveCount member is less than or equal to the corresponding element of pMaxPrimitiveCounts.
  • For each element of either pGeometries or ppGeometries at a given index, with a geometryType member equal to VK_GEOMETRY_TYPE_TRIANGLES_KHR, if the pNext chain contains VkAccelerationStructureTrianglesOpacityMicromapEXT the corresponding member of pBuildInfo also contains VkAccelerationStructureTrianglesOpacityMicromapEXT and with an equivalent micromap.
  • For each element of either pGeometries or ppGeometries at a given index, with a geometryType member equal to VK_GEOMETRY_TYPE_TRIANGLES_KHR, if the pNext chain contains VkAccelerationStructureTrianglesDisplacementMicromapNV the corresponding member of pBuildInfo also contains VkAccelerationStructureTrianglesDisplacementMicromapNV and with an equivalent micromap.

Similarly, the updateScratchSize value will support any build command specifying the VK_BUILD_ACCELERATION_STRUCTURE_MODE_UPDATE_KHR

mode under the above conditions, and the buildScratchSize value will support any build command specifying the VK_BUILD_ACCELERATION_STRUCTURE_MODE_BUILD_KHR mode under the above conditions.