public Color[] Decompress(byte[] blockData)
{
Debug.Assert(blockData.Length == BlockFormat.BC2ByteSize);
var block = BC2BlockData.FromBytes(blockData);
var colorTable = BC1ColorTable.Create(block.Color0, block.Color1);
var colors = new Color[BlockFormat.TexelCount];
for (int i = 0; i < colors.Length; ++i)
{
int index = block.ColorIndexes[i];
int alpha = block.ColorAlphas[i];
// Convert 4-bit alpha to 8-bit by shifting the bits left and ORing
// with the most significant bits to calculate the remaining values
alpha = (alpha << 4) | (alpha & 0x0F);
var color16 = colorTable[index];
var color32 = Color.FromArgb(alpha, ColorUtility.To32Bit(color16));
colors[i] = color32;
}
return(colors);
}
/// <summary>
/// Instantiates a <see cref="BC2BlockData"/> from compressed BC2 block data.
/// </summary>
/// <param name="bytes">The data of a BC2 compressed block.</param>
public static BC2BlockData FromBytes(byte[] bytes)
{
Debug.Assert(bytes.Length == BlockFormat.BC2ByteSize,
"Mismatching number of bytes for format.");
byte[,] alphas = new byte[4, 2];
alphas[0, 0] = bytes[0];
alphas[0, 1] = bytes[1];
alphas[1, 0] = bytes[2];
alphas[1, 1] = bytes[3];
alphas[2, 0] = bytes[4];
alphas[2, 1] = bytes[5];
alphas[3, 0] = bytes[6];
alphas[3, 1] = bytes[7];
byte c0Low = bytes[8];
byte c0Hi = bytes[9];
byte c1Low = bytes[10];
byte c1Hi = bytes[11];
byte[] indexes = new byte[4];
indexes[0] = bytes[12];
indexes[1] = bytes[13];
indexes[2] = bytes[14];
indexes[3] = bytes[15];
var block = new BC2BlockData();
block.Color0 = Color565.FromValue((ushort)((c0Hi << 8) | c0Low));
block.Color1 = Color565.FromValue((ushort)((c1Hi << 8) | c1Low));
for (int p = 0, row = 0; p < BlockFormat.TexelCount; p += BlockFormat.Dimension, ++row)
{
int a = p;
int b = p + 1;
int c = p + 2;
int d = p + 3;
block.ColorIndexes[a] = indexes[row] & 0x03;
block.ColorIndexes[b] = (indexes[row] >> 2) & 0x03;
block.ColorIndexes[c] = (indexes[row] >> 4) & 0x03;
block.ColorIndexes[d] = (indexes[row] >> 6) & 0x03;
block.ColorAlphas[a] = (byte)(alphas[row, 1] & 0x0F);
block.ColorAlphas[b] = (byte)((alphas[row, 1] & 0xF0) >> 4);
block.ColorAlphas[c] = (byte)(alphas[row, 0] & 0x0F);
block.ColorAlphas[d] = (byte)((alphas[row, 0] & 0xF0) >> 4);
}
return(block);
}
public byte[] Compress(Color[] colors)
{
Debug.Assert(colors.Length == BlockFormat.TexelCount);
var colorSpace = new ColorSpace(colors);
var colorTable = BC1ColorTable.Create(colorSpace.MaxColor, colorSpace.MinColor);
var block = new BC2BlockData();
block.Color0 = colorTable[0];
block.Color1 = colorTable[1];
for (int i = 0; i < colors.Length; ++i)
{
var color32 = colors[i];
var color16 = ColorUtility.To16Bit(color32);
block.ColorIndexes[i] = ColorUtility.GetIndexOfClosestColor(colorTable, color16);
block.ColorAlphas[i] = color32.A >> 4; // Convert 8-bit alpha to 4-bit
}
return(block.ToBytes());
}
