WCT (World Compressed Texture)

Header

• 1 byte - Compression type: 0x12: zlib, 0x13: lzss
• 1 byte - version
• 1 byte - bit count
• 1 byte - unknown
• 2 bytes - width
• 2 bytes - height
• 2 bytes - Y channel quantization scale
• 2 bytes - Cb channel quantization scale
• 2 bytes - Cr channel quantization scale
• 2 bytes - A channel quantization scale
• 4 bytes - block 0 size
• 4 bytes - block 1 size
• 4 bytes - unknown

Decoding Image

1. Get aligned width / height

uint32_t GetAlignedSize(uint32_t size)
{
 uint32_t value = (size - 1);
 uint32_t n = 1;
 for (; (value >>= 1) != 0;){
  ++n;
 }
 if (n < 3){
  n = 3;
 }
 return 1 << n;
}

2. Calc max size (largest of aligned width / height)
3. Set up quantization values

float float8 = 1.0f - ((float)header.YChannelQuantizationScale * -0.5f);
float floatA = 1.0f - ((float)header.CbChannelQuantizationScale * -0.25f);
float floatC = 1.0f - ((float)header.CrChannelQuantizationScale * -0.25f);
float floatE = (float)header.AChannelQuantizationScale + 1.0f;

4. Decompress

LZSS:

result := []
while true:
  isDelta := GetBit( 1 )
  if isDelta:
    literalValue := GetBits( 8 )
    push literalValue to result
  else:
    offset := GetBits( 12 )
    length := GetBits( 7 ) + 1
    
    if offset == 0:
      break
    for 0..length:
      push result[ current - offset ] to result

5. Decode channels using quantization scales Cb/Cr use size / 2

6. Convert YCbCr values to RGB