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52 lines
1.7 KiB
C++
52 lines
1.7 KiB
C++
#pragma once
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#include <cstdint>
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namespace Pica {
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struct ZOrderOffset {
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static constexpr uint32_t block_width = 8;
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static constexpr uint32_t block_height = 8;
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uint32_t texel_within_tile;
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uint32_t coarse_x;
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uint32_t coarse_y;
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};
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inline ZOrderOffset ZOrderTileOffset(uint32_t x, uint32_t y) {
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// Images are split into 8x8 tiles. Each tile is composed of four 4x4 subtiles each
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// of which is composed of four 2x2 subtiles each of which is composed of four texels.
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// Each structure is embedded into the next-bigger one in a diagonal pattern, e.g.
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// texels are laid out in a 2x2 subtile like this:
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// 2 3
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// 0 1
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//
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// The full 8x8 tile has the texels arranged like this:
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//
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// 42 43 46 47 58 59 62 63
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// 40 41 44 45 56 57 60 61
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// 34 35 38 39 50 51 54 55
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// 32 33 36 37 48 49 52 53
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// 10 11 14 15 26 27 30 31
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// 08 09 12 13 24 25 28 29
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// 02 03 06 07 18 19 22 23
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// 00 01 04 05 16 17 20 21
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// TODO: More flexible encoding algorithms exist for this!
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uint32_t texel_index_within_tile = 0;
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for (int block_size_index = 0; block_size_index < 3; ++block_size_index) {
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int sub_tile_width = 1 << block_size_index;
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int sub_tile_height = 1 << block_size_index;
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int sub_tile_index = (x & sub_tile_width) << block_size_index;
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sub_tile_index += 2 * ((y & sub_tile_height) << block_size_index);
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texel_index_within_tile += sub_tile_index;
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}
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uint32_t coarse_x = (x / ZOrderOffset::block_width) * ZOrderOffset::block_width;
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uint32_t coarse_y = (y / ZOrderOffset::block_height) * ZOrderOffset::block_height;
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return { texel_index_within_tile, coarse_x, coarse_y };
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}
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} // namespace Pica
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