Add ktx

2026-06-14 19:09:18 +01:00
parent 14bd1a9271
commit 13fa90a0e9
3958 changed files with 999286 additions and 4 deletions
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+# The .astc File Format
+
+The default file format for compressed textures generated by `astcenc`, as well
+as from many other ASTC compressors, is the `.astc` format. This is a very
+simple format consisting of a small header followed immediately by the binary
+payload for a single image surface.
+
+Header
+======
+
+The header is a fixed 16 byte structure, defined as storing only bytes to avoid
+any endianness issues or incur any padding overhead.
+
+```
+struct astc_header
+{
+    uint8_t magic[4];
+    uint8_t block_x;
+    uint8_t block_y;
+    uint8_t block_z;
+    uint8_t dim_x[3];
+    uint8_t dim_y[3];
+    uint8_t dim_z[3];
+};
+```
+
+Magic number
+------------
+
+The 4 byte magic number at the start of the file acts as a format identifier.
+
+```
+    magic[0] = 0x13;
+    magic[1] = 0xAB;
+    magic[2] = 0xA1;
+    magic[3] = 0x5C;
+```
+
+Block size
+----------
+
+The `block_*` fields store the ASTC block dimensions in texels. For 2D images
+the Z dimension must be set to 1.
+
+Image dimensions
+----------------
+
+The `dim_*` fields store the image dimensions in texels.  For 2D images the
+Z dimension must be set to 1.
+
+Note that the image is not required to be an exact multiple of the compressed
+block size; the compressed data may include padding that is discarded during
+decompression.
+
+Each dimension is a 24 bit unsigned value that is reconstructed from the stored
+byte values as:
+
+```
+decoded_dim = dim[0] + (dim[1] << 8) + (dim[2] << 16);
+```
+
+Binary payload
+==============
+
+The binary payload is a byte stream that immediately follows the header. It
+contains 16 bytes per compressed block. The number of compressed blocks is
+determined from the header information.
+
+- - -
+
+_Copyright © 2020-2022, Arm Limited and contributors. All rights reserved._