DX10 DDS files using the BC (block compression) formats were reported as
unsupported: knownDXGIFormat() only mapped the floating point DXGI
formats, so getFormat() returned FormatUnknown and ensureScanned() failed,
e.g. for a BC7_UNORM_SRGB (dxgi 99) image.
The following changes have been made:
- Added a self-contained BC7 decoder following the "BC7 Format"
specification, supporting all 8 modes, for both the UNORM and the
UNORM_SRGB variants (loaded as ARGB32)
- Added BC4 support (single channel, loaded as Grayscale8)
- Added BC5 support, reusing the existing ATI2/3Dc normal map decoder
- Added DX10 mappings for BC1/BC2/BC3, which were previously handled only
as the legacy DXT1/DXT3/DXT5 fourCC formats
- Added read tests for BC4, BC5, BC7 and BC7_UNORM_SRGB, plus DX10
variants of the existing BC1/BC2/BC3 test images
BC6H (HDR) is not supported.
The test data was generated from the existing rgba.png test image, encoded
with bc7enc_rdo and decoded with bcdec.
BUG: 524495
