/// <summary>
/// Instantiates a <see cref="BC1BlockData"/> from compressed BC1 block data.
/// </summary>
/// <param name="bytes">The data of a BC1 compressed block.</param>
public static BC1BlockData FromBytes(byte[] bytes)
{
Debug.Assert(bytes.Length == BlockFormat.BC1ByteSize,
"Mismatching number of bytes for format.");
byte c0Low = bytes[0];
byte c0Hi = bytes[1];
byte c1Low = bytes[2];
byte c1Hi = bytes[3];
byte[] indexes = new byte[4];
indexes[0] = bytes[4];
indexes[1] = bytes[5];
indexes[2] = bytes[6];
indexes[3] = bytes[7];
var block = new BC1BlockData();
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)
{
block.ColorIndexes[p] = indexes[row] & 0x03;
block.ColorIndexes[p + 1] = (indexes[row] >> 2) & 0x03;
block.ColorIndexes[p + 2] = (indexes[row] >> 4) & 0x03;
block.ColorIndexes[p + 3] = (indexes[row] >> 6) & 0x03;
}
return(block);
}
public byte[] Compress(Color[] colors)
{
Debug.Assert(colors.Length == BlockFormat.TexelCount);
var colorTable = CreateColorTable(colors);
var block = new BC1BlockData();
block.Color0 = colorTable[0];
block.Color1 = colorTable[1];
for (int i = 0; i < colors.Length; ++i)
{
var color32 = colors[i];
// If color has alpha, use a specific index
// to identify the color when decompressed
block.ColorIndexes[i] = color32.HasAlpha() ? AlphaColorIndex :
ColorUtility.GetIndexOfClosestColor(colorTable, ColorUtility.To16Bit(color32));
}
return(block.ToBytes());
}
public Color[] Decompress(byte[] blockData)
{
Debug.Assert(blockData.Length == BlockFormat.BC1ByteSize);
var block = BC1BlockData.FromBytes(blockData);
var colorTable = CreateColorTable(block.Color0, block.Color1);
var is1BitAlpha = colorTable[0].Value <= colorTable[1].Value;
var colors = new Color[BlockFormat.TexelCount];
for (int i = 0; i < colors.Length; ++i)
{
int index = block.ColorIndexes[i];
int alpha = is1BitAlpha && index == AlphaColorIndex ? 0 : 255;
var color16 = colorTable[index];
var color32 = Color.FromArgb(alpha, ColorUtility.To32Bit(color16));
colors[i] = color32;
}
return(colors);
}
