Function EmitAlphaIndices

trinity/Tr2DxtCompressor.cpp:378–419

}

void EmitAlphaIndices( const uint8_t* colorBlock, const uint8_t minAlpha, const uint8_t maxAlpha, uint8_t** outBuff )
{

	CCP_ASSERT( maxAlpha >= minAlpha );

	const int ALPHA_RANGE = 7;

	uint8_t mid, ab1, ab2, ab3, ab4, ab5, ab6, ab7;
	uint8_t indexes[16];

	mid = ( maxAlpha - minAlpha ) / ( 2 * ALPHA_RANGE );

	ab1 = minAlpha + mid;
	ab2 = ( 6 * maxAlpha + 1 * minAlpha ) / ALPHA_RANGE + mid;
	ab3 = ( 5 * maxAlpha + 2 * minAlpha ) / ALPHA_RANGE + mid;
	ab4 = ( 4 * maxAlpha + 3 * minAlpha ) / ALPHA_RANGE + mid;
	ab5 = ( 3 * maxAlpha + 4 * minAlpha ) / ALPHA_RANGE + mid;
	ab6 = ( 2 * maxAlpha + 5 * minAlpha ) / ALPHA_RANGE + mid;
	ab7 = ( 1 * maxAlpha + 6 * minAlpha ) / ALPHA_RANGE + mid;

	for( int i = 0; i < 16; i++ )
	{
		uint8_t a = colorBlock[i * 4 + 3];
		int b1 = ( a <= ab1 );
		int b2 = ( a <= ab2 );
		int b3 = ( a <= ab3 );
		int b4 = ( a <= ab4 );
		int b5 = ( a <= ab5 );
		int b6 = ( a <= ab6 );
		int b7 = ( a <= ab7 );
		int index = ( b1 + b2 + b3 + b4 + b5 + b6 + b7 + 1 ) & 7;
		indexes[i] = index ^ ( 2 > index );
	}

	EmitByte( ( indexes[0] >> 0 ) | ( indexes[1] << 3 ) | ( indexes[2] << 6 ), outBuff );
	EmitByte( ( indexes[2] >> 2 ) | ( indexes[3] << 1 ) | ( indexes[4] << 4 ) | ( indexes[5] << 7 ), outBuff );
	EmitByte( ( indexes[5] >> 1 ) | ( indexes[6] << 2 ) | ( indexes[7] << 5 ), outBuff );

	EmitByte( ( indexes[8] >> 0 ) | ( indexes[9] << 3 ) | ( indexes[10] << 6 ), outBuff );
	EmitByte( ( indexes[10] >> 2 ) | ( indexes[11] << 1 ) | ( indexes[12] << 4 ) | ( indexes[13] << 7 ), outBuff );
	EmitByte( ( indexes[13] >> 1 ) | ( indexes[14] << 2 ) | ( indexes[15] << 5 ), outBuff );
}

void EmitColorIndices( const uint8_t* colorBlock, const uint8_t* minColor, const uint8_t* maxColor, uint8_t** outBuff )
{