VkMicromapBuildInfoEXT

The VkMicromapBuildInfoEXT structure is defined as:

typedef struct VkMicromapBuildInfoEXT {
    VkStructureType sType;
    const void* pNext;
    VkMicromapTypeEXT type;
    VkBuildMicromapFlagsEXT flags;
    VkBuildMicromapModeEXT mode;
    VkMicromapEXT dstMicromap;
    uint32_t usageCountsCount;
    const VkMicromapUsageEXT* pUsageCounts;
    const VkMicromapUsageEXT* const* ppUsageCounts;
    VkDeviceOrHostAddressConstKHR data;
    VkDeviceOrHostAddressKHR scratchData;
    VkDeviceOrHostAddressConstKHR triangleArray;
    VkDeviceSize triangleArrayStride;
} VkMicromapBuildInfoEXT;

• sType is a VkStructureType value identifying this structure.
• pNext is NULL or a pointer to a structure extending this structure.
• type is a VkMicromapTypeEXT value specifying the type of micromap being built.
• flags is a bitmask of VkBuildMicromapFlagBitsEXT specifying additional parameters of the micromap.
• mode is a VkBuildMicromapModeEXT value specifying the type of operation to perform.
• dstMicromap is a pointer to the target micromap for the build.
• usageCountsCount specifies the number of usage counts structures that will be used to determine the size of this micromap.
• pUsageCounts is a pointer to an array of VkMicromapUsageEXT structures.
• ppUsageCounts is a pointer to an array of pointers to VkMicromapUsageEXT structures.
• data is the device or host address to memory which contains the data for the micromap.
• scratchData is the device or host address to memory that will be used as scratch memory for the build.
• triangleArray is the device or host address to memory containing the VkMicromapTriangleEXT data
• triangleArrayStride is the stride in bytes between each element of triangleArray

Only one of pUsageCounts or ppUsageCounts can be a valid pointer, the other must be NULL. The elements of the non-NULL array describe the total counts used to build each micromap. Each element contains a count which is the number of micromap triangles of that format and subdivisionLevel contained in the micromap. Multiple elements with the same format and subdivisionLevel are allowed and the total count for that format and subdivisionLevel is the sum of the count for each element.

Each micromap triangle refers to one element in triangleArray which contains the format and subdivisionLevel for that particular triangle as well as a dataOffset in bytes which is the location relative to data where that triangle’s micromap data begins. The data at triangleArray is laid out as a 4 byte unsigned integer for the dataOffset followed by a 2 byte unsigned integer for the subdivision level then a 2 byte unsigned integer for the format. In practice, compilers compile VkMicromapTriangleEXT to match this pattern.

For opacity micromaps, the data at data is packed as either one bit per element for VK_OPACITY_MICROMAP_FORMAT_2_STATE_EXT or two bits per element for VK_OPACITY_MICROMAP_FORMAT_4_STATE_EXT and is packed from LSB to MSB in each byte. The data at each index in those bytes is interpreted as discussed in Ray Opacity Micromap.

For displacement micromaps, the data at data is interpreted as discussed in Displacement Micromap Encoding.