/// <summary>
/// Decompresses an image.
/// </summary>
/// <param name="width">The width of the image to decompress.</param>
/// <param name="height">The height of the image to decompress.</param>
/// <param name="data">The compressed image data.</param>
/// <param name="flags">The compression flags.</param>
/// <returns>Returns the decompressed image as a byte array in the 32Bit RGBA-Format.</returns>
internal static byte[] DecompressImage(int width, int height, byte[] data, DxtFlags flags)
{
var rgba = new byte[width * height * 4];
// initialise the block input
var sourceBlock_pos = 0;
var bytesPerBlock = (flags & DxtFlags.DXT1) != 0 ? 8 : 16;
var targetRGBA = new byte[4 * 16];
// loop over blocks
for (var y = 0; y < height; y += 4)
{
for (var x = 0; x < width; x += 4)
{
// decompress the block
var targetRGBA_pos = 0;
if (data.Length == sourceBlock_pos)
{
continue;
}
Decompress(targetRGBA, data, sourceBlock_pos, flags);
// Write the decompressed pixels to the correct image locations
for (var py = 0; py < 4; py++)
{
for (var px = 0; px < 4; px++)
{
var sx = x + px;
var sy = y + py;
if (sx < width && sy < height)
{
var targetPixel = 4 * ((width * sy) + sx);
rgba[targetPixel + 0] = targetRGBA[targetRGBA_pos + 0];
rgba[targetPixel + 1] = targetRGBA[targetRGBA_pos + 1];
rgba[targetPixel + 2] = targetRGBA[targetRGBA_pos + 2];
rgba[targetPixel + 3] = targetRGBA[targetRGBA_pos + 3];
targetRGBA_pos += 4;
}
else
{
// Ignore that pixel
targetRGBA_pos += 4;
}
}
}
sourceBlock_pos += bytesPerBlock;
}
}
return(rgba);
}
private static void Decompress(byte[] rgba, byte[] block, int blockIndex, DxtFlags flags)
{
// get the block locations
var colorBlockIndex = blockIndex;
if ((flags & (DxtFlags.DXT3 | DxtFlags.DXT5)) != 0)
{
colorBlockIndex += 8;
}
// decompress color
DecompressColor(rgba, block, colorBlockIndex, (flags & DxtFlags.DXT1) != 0);
// decompress alpha separately if necessary
if ((flags & DxtFlags.DXT3) != 0)
{
DecompressAlphaDxt3(rgba, block, blockIndex);
}
else if ((flags & DxtFlags.DXT5) != 0)
{
DecompressAlphaDxt5(rgba, block, blockIndex);
}
}
