Function CompressNormalMapDXT5NoAlpha

trinity/Tr2DxtCompressor.cpp:757–793

below works fine, but doesn't support a material id in the alpha channel

// below works fine, but doesn't support a material id in the alpha channel
void CompressNormalMapDXT5NoAlpha( const uint8_t* inBuf, uint8_t* outBuf, int width, int height, ptrdiff_t& outputBytes, volatile const bool& cancel )
{
	uint8_t block[64];
	uint8_t normalMin[4];
	uint8_t normalMax[4];

	uint8_t** outData = &outBuf;

	for( int j = 0; j < height; j += 4, inBuf += width * 4 * 4 )
	{
		if( cancel )
		{
			return;
		}
		for( int i = 0; i < width; i += 4 )
		{

			ExtractBlock( inBuf + i * 4, width, block );

			GetMinMaxNormalsBBox( block, normalMin, normalMax );
			InsetNormalsBBoxDXT5( normalMin, normalMax );

			// Write out Nx into alpha channel.
			// Note: all code in this file assumes TRIFMT_A8R8G8B8, so red is at [2]
			EmitByte( normalMax[0], outData );
			EmitByte( normalMin[0], outData );
			EmitAlphaIndicesForNormals( block, 2, normalMin[0], normalMax[0], outData );

			// Write out Ny into green channel.
			EmitWord( NormalYTo565( normalMax[1] ), outData );
			EmitWord( NormalYTo565( normalMin[1] ), outData );
			EmitGreenIndices( block, 1, normalMin[1], normalMax[1], outData );
		}
	}

	outputBytes = *outData - outBuf;
}

void CompressNormalMap3Dc( const uint8_t* inBuf, uint8_t* outBuf, int width, int height, ptrdiff_t& outputBytes, volatile const bool& cancel )
{