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-rw-r--r--src/video_core/utils.h50
1 files changed, 50 insertions, 0 deletions
diff --git a/src/video_core/utils.h b/src/video_core/utils.h
index 6fd640425..bda793fa5 100644
--- a/src/video_core/utils.h
+++ b/src/video_core/utils.h
@@ -35,4 +35,54 @@ struct TGAHeader {
*/
void DumpTGA(std::string filename, short width, short height, u8* raw_data);
+/**
+ * Interleave the lower 3 bits of each coordinate to get the intra-block offsets, which are
+ * arranged in a Z-order curve. More details on the bit manipulation at:
+ * https://fgiesen.wordpress.com/2009/12/13/decoding-morton-codes/
+ */
+static inline u32 MortonInterleave(u32 x, u32 y) {
+ u32 i = (x & 7) | ((y & 7) << 8); // ---- -210
+ i = (i ^ (i << 2)) & 0x1313; // ---2 --10
+ i = (i ^ (i << 1)) & 0x1515; // ---2 -1-0
+ i = (i | (i >> 7)) & 0x3F;
+ return i;
+}
+
+/**
+ * Calculates the offset of the position of the pixel in Morton order
+ */
+static inline u32 GetMortonOffset(u32 x, u32 y, u32 bytes_per_pixel) {
+ // Images are split into 8x8 tiles. Each tile is composed of four 4x4 subtiles each
+ // of which is composed of four 2x2 subtiles each of which is composed of four texels.
+ // Each structure is embedded into the next-bigger one in a diagonal pattern, e.g.
+ // texels are laid out in a 2x2 subtile like this:
+ // 2 3
+ // 0 1
+ //
+ // The full 8x8 tile has the texels arranged like this:
+ //
+ // 42 43 46 47 58 59 62 63
+ // 40 41 44 45 56 57 60 61
+ // 34 35 38 39 50 51 54 55
+ // 32 33 36 37 48 49 52 53
+ // 10 11 14 15 26 27 30 31
+ // 08 09 12 13 24 25 28 29
+ // 02 03 06 07 18 19 22 23
+ // 00 01 04 05 16 17 20 21
+ //
+ // This pattern is what's called Z-order curve, or Morton order.
+
+ const unsigned int block_width = 8;
+ const unsigned int block_height = 8;
+
+ const unsigned int coarse_x = x & ~7;
+ const unsigned int coarse_y = y & ~7;
+
+ u32 i = VideoCore::MortonInterleave(x, y);
+
+ const unsigned int offset = coarse_x * block_height;
+
+ return (i + offset) * bytes_per_pixel;
+}
+
} // namespace