private static unsafe byte[] DecompressDXT1(DDSStruct header, byte[] data, DDSPixelFormat pixelFormat)
{
// allocate bitmap
int bpp = (int)(DDSHelper.PixelFormatToBpp(pixelFormat, header.pixelformat.rgbbitcount));
int bps = (int)(header.width * bpp * DDSHelper.PixelFormatToBpc(pixelFormat));
int sizeofplane = (int)(bps * header.height);
int width = (int)header.width;
int height = (int)header.height;
int depth = (int)header.depth;
// DXT1 decompressor
byte[] rawData = new byte[depth * sizeofplane + height * bps + width * bpp];
Colour8888[] colours = new Colour8888[4];
colours[0].alpha = 0xFF;
colours[1].alpha = 0xFF;
colours[2].alpha = 0xFF;
fixed(byte *bytePtr = data)
{
byte *temp = bytePtr;
for (int z = 0; z < depth; z++)
{
for (int y = 0; y < height; y += 4)
{
for (int x = 0; x < width; x += 4)
{
ushort colour0 = *((ushort *)temp);
ushort colour1 = *((ushort *)(temp + 2));
DDSHelper.DxtcReadColor(colour0, ref colours[0]);
DDSHelper.DxtcReadColor(colour1, ref colours[1]);
uint bitmask = ((uint *)temp)[1];
temp += 8;
if (colour0 > colour1)
{
// Four-color block: derive the other two colors.
// 00 = color_0, 01 = color_1, 10 = color_2, 11 = color_3
// These 2-bit codes correspond to the 2-bit fields
// stored in the 64-bit block.
colours[2].blue = (byte)((2 * colours[0].blue + colours[1].blue + 1) / 3);
colours[2].green = (byte)((2 * colours[0].green + colours[1].green + 1) / 3);
colours[2].red = (byte)((2 * colours[0].red + colours[1].red + 1) / 3);
//colours[2].alpha = 0xFF;
colours[3].blue = (byte)((colours[0].blue + 2 * colours[1].blue + 1) / 3);
colours[3].green = (byte)((colours[0].green + 2 * colours[1].green + 1) / 3);
colours[3].red = (byte)((colours[0].red + 2 * colours[1].red + 1) / 3);
colours[3].alpha = 0xFF;
}
else
{
// Three-color block: derive the other color.
// 00 = color_0, 01 = color_1, 10 = color_2,
// 11 = transparent.
// These 2-bit codes correspond to the 2-bit fields
// stored in the 64-bit block.
colours[2].blue = (byte)((colours[0].blue + colours[1].blue) / 2);
colours[2].green = (byte)((colours[0].green + colours[1].green) / 2);
colours[2].red = (byte)((colours[0].red + colours[1].red) / 2);
//colours[2].alpha = 0xFF;
colours[3].blue = (byte)((colours[0].blue + 2 * colours[1].blue + 1) / 3);
colours[3].green = (byte)((colours[0].green + 2 * colours[1].green + 1) / 3);
colours[3].red = (byte)((colours[0].red + 2 * colours[1].red + 1) / 3);
colours[3].alpha = 0x00;
}
for (int j = 0, k = 0; j < 4; j++)
{
for (int i = 0; i < 4; i++, k++)
{
int select = (int)((bitmask & (0x03 << k * 2)) >> k * 2);
Colour8888 col = colours[select];
if (((x + i) < width) && ((y + j) < height))
{
uint offset = (uint)(z * sizeofplane + (y + j) * bps + (x + i) * bpp);
rawData[offset + 0] = (byte)col.red;
rawData[offset + 1] = (byte)col.green;
rawData[offset + 2] = (byte)col.blue;
rawData[offset + 3] = (byte)col.alpha;
}
}
}
}
}
}
}
return(rawData);
}
