FMipLevelStreamingInfo

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Describes a mip level of a SVT frame in terms of the sizes and offsets of the data in the built bulk data. Each mip level consists of 4 buffer sections:

Page table data is stored as two consecutive uint32 arrays, where the first array stores packed coordinates into the page table. The second array stores the physical tile indices to be written to the page table. Only non-zero page table entries are stored.

Since often about 30%-50% of all voxels in the physical tiles have values equal to the fallback value, the tile data (voxels) is also compressed. For each tile, a bit mask with one bit per voxel is stored (occupancy bits). A set bit indicates that the voxel is actually stored and not equal to the fallback value. When streaming in the data, the compressed voxel data is expanded on the GPU in the upload shader. This bit mask costs 183 uint32 -> 732 bytes. A full 18x18x18 tile (16+2 padding) of 8bit unorm data is 5832 bytes, so if 30%-50% of that can be saved, then paying 732 bytes for the occupancy bits should almost always be worth it.

Due to the above compression technique, the start offset of the voxel data for a given tile can now no longer be computed as NumVoxelsPerPaddedTile * TileIndex, so a precomputed offset into the shared array of voxel data is needed (tile data offsets). This means that we need to store one additional uint32 per tile, arriving at a total overhead of 736 bytes per tile.

Finally there is the actual voxel data, which is simply the all non-fallback voxels in contiguous memory.

Syntax

struct FMipLevelStreamingInfo  
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struct FMipLevelStreamingInfo

Variables

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