bcdec

Small header-only C library to decompress any BC compressed image inspired by incredible stb libaries (http://nothings.org/stb)

Written by Sergii "iOrange" Kudlai in 2022.

This library provides functions to decompress blocks of BC compressed images.

This library does not allocate memory and is trying to use as less stack as possible.

The library was never optimized specifically for speed but for the overall size.
It has zero external dependencies and is not using any runtime functions.

Supported BC formats:

• BC1 (also known as DXT1) + it's "binary alpha" variant BC1A (DXT1A)
• BC2 (also known as DXT3)
• BC3 (also known as DXT5)
• BC4 (also known as ATI1N)
• BC5 (also known as ATI2N)
• BC6H (HDR format)
• BC7

BC1/BC2/BC3/BC7 are expected to decompress into 4*4 RGBA blocks 8bit per component (32bit pixel)
BC4/BC5 are expected to decompress into 4*4 R/RG blocks 8bit per component (8bit and 16bit pixel)
BC6H is expected to decompress into 4*4 RGB blocks of either 32bit float or 16bit "half" per component (96bit or 48bit pixel)

You will also find included test program that converts compressed DDS files into TGA/HDR.
It is a good start to learn on how to use the bcdec library.
It comes with some test images in the test_images folder and a batch script test_bcdec.bat to run over them.

Used HDRI image "Lythwood Room" from https://polyhaven.com/a/lythwood_room licensed under CC0 license.

CREDITS:

• Aras Pranckevičius (@aras-p)

  • BC1/BC3 decoders optimizations (up to 3x the speed)
  • BC6H/BC7 bits pulling routines optimizations
  • optimized BC6H by moving unquantize out of the loop
  • Split BC6H decompression function into 'half' and 'float' variants

• Michael Schmidt (@RunDevelopment)

  • Found better "magic" coefficients for integer interpolation of reference colors in BC1 color block, that match with the floating point interpolation. This also made it faster than integer division by 3!