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Using Basis Universal to decompress any supported GPU texture format

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Rich Geldreich edited this page Mar 21, 2020 · 12 revisions

The Basis Universal encoder codebase contains easy to use code to unpack the following compressed GPU texture formats:

  • BC7 - Fully supported
  • ASTC - LDR only (HDR support is in the code, but remarked out until we need it.)

Our high-level helpers only support 4x4 block size, but you can access the low-level ASTC code directly (in basisu_astc_decomp.h) to unpack other ASTC block sizes.

  • BC1-5 - Fully supported
  • ETC1 - Fully supported
  • ETC2 RGB/RGBA8 - Only supports ETC1 for color data (no planar, T/H modes), alpha data is fully supported
  • ETC2 EAC R11/RG11 - Fully supported
  • PVRTC1 4bpp RGB/RGBA - Fully supported. Decompression has been verified against PVRTexTool's output for correctness.
  • PVRTC2 - Limited support. Just the non-interpolated mode our transcoders use.
  • ATC RGB/RGBA - Fully supported
  • FXT1 - Limited support (just the mode we use)

Before you can unpack textures, be sure to call basisu_encoder_init() once at startup.

To unpack individual 4x4 (or 8x4 for FXT1) texel blocks to raw RGBA pixels, use this function:

bool basisu::unpack_block(texture_format fmt, const void *pBlock, color_rgba *pPixels);

This doesn't work on PVRTC1 textures, because the decoder needs access to the surrounding blocks. Alternately, you can create a basisu::gpu_image object, then call gpu_image::unpack(). This works on any supported format, including PVRTC1.

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