# Texture codec for johnmcm.com

The WebAssembly module behind johnmcm.com's DDS Converter (/dds-converter):
it decodes and encodes the BC (DXT) block-compressed texture formats.

- Decoding: [bcdec](https://github.com/iOrange/bcdec) by Sergii Kudlai, at
  commit `80859ed3b7afb1c527a2a99d70c61457bea72d0c` (MIT or Unlicense).
- Encoding: rgbcx (BC1, BC3, BC4, BC5) and bc7enc (BC7) from
  [bc7enc_rdo](https://github.com/richgel999/bc7enc_rdo) by Richard
  Geldreich, Jr., at commit `b9438627eef73a1157e84201b6fa6eb2ffd6d9f0`
  (MIT or public domain).

What is here:

- `source/`: the exact library files built, unmodified, with their licences.
- `src/wrapper.cpp`: this site's functions for the page: decode a surface to
  RGBA, encode a range of block rows, and one correction to bc7enc's output
  (opaque blocks it writes in mode 6 can decode with alpha 254; the wrapper
  sets those blocks' alpha endpoints and p-bits so alpha is exactly 255).
- `Dockerfile` and `build.ps1`: the build, with the Emscripten image pinned
  by digest and both libraries by commit. Run `build.ps1` with Docker Desktop
  running; the module goes to `frontend/vendor/local/dds@1/`.

DDS and TGA headers, the uncompressed pixel formats, mipmaps and PNG are
handled in TypeScript by the page itself (frontend/src/app/dds-converter/).