// BC5
internal static void DecompressATI2Block(byte[] source, int sourceStart, byte[] destination, int decompressedStart, int decompressedLineLength, bool unused)
{
// Green = +1
DDS_BlockHelpers.Decompress8BitBlock(source, sourceStart, destination, decompressedStart + 1, decompressedLineLength, false);
// Red = +2, source + 8 to skip first compressed block.
DDS_BlockHelpers.Decompress8BitBlock(source, sourceStart + 8, destination, decompressedStart + 2, decompressedLineLength, false);
// KFreon: Alpha is 255, and blue needs to be calculated
for (int i = 0; i < 16; i++)
{
int offset = GetDecompressedOffset(decompressedStart, decompressedLineLength, i);
// Get Red and Green on the range -1 - 1
// *2-1 moves the range from 0 - 1, to -1 - 1
double green = (destination[offset + 1] / 127.5d) - 1d;
double red = (destination[offset + 2] / 127.5d) - 1d;
// Z solution for: x2 + y2 + z2 = 1, unit normal vectors. Only consider +ve root as ATI2 is a tangent space mapping and Z must be +ve.
// Also when 1 - x2 - y2 < 0, Z = NaN, but is compensated for in ExpandTo255.
double Z = Math.Sqrt(1d - (red * red + green * green));
destination[offset] = ExpandTo255(Z); // Blue
destination[offset + 3] = 255; // Alpha
}
}
internal static void DecompressBC3Block(byte[] source, int sourceStart, byte[] destination, int decompressedStart, int decompressedLineLength, bool isPremultiplied)
{
// Alpha, +3 to select that channel.
DDS_BlockHelpers.Decompress8BitBlock(source, sourceStart, destination, decompressedStart + 3, decompressedLineLength, false);
// RGB
DDS_BlockHelpers.DecompressRGBBlock(source, sourceStart + 8, destination, decompressedStart, decompressedLineLength, false, isPremultiplied);
}
// BC4
internal static void DecompressATI1Block(byte[] source, int sourceStart, byte[] destination, int decompressedStart, int decompressedLineLength, bool unused)
{
DDS_BlockHelpers.Decompress8BitBlock(source, sourceStart, destination, decompressedStart, decompressedLineLength, false);
// KFreon: All channels are the same to make grayscale, and alpha needs to be 255.
for (int i = 0; i < 16; i++)
{
int offset = GetDecompressedOffset(decompressedStart, decompressedLineLength, i);
// Since one channel (blue) was set by the decompression above, just need to set the remaining channels
destination[offset + 1] = destination[offset];
destination[offset + 2] = destination[offset];
destination[offset + 3] = 255; // Alpha
}
}
internal static void DecompressBC2Block(byte[] source, int sourceStart, byte[] destination, int decompressedStart, int decompressedLineLength, bool isPremultiplied)
{
// KFreon: Decompress alpha (only half of the texel count though, since each byte is 2 texels of alpha)
for (int i = 0; i < 8; i++)
{
// Start + alphaOffset + lineOffset.
// DecompressedStart = Top Left corner of texel in full image in bytes.
// alphaOffset = effectively column offset in a row of bitmap. Since a compressed byte has 2 pixels worth of alpha, i % 2 * 8 skips 2 pixels of BGRA each byte read, +3 selects alpha channel.
// lineOffset = texels aren't contiguous i.e. each row in texel isn't next to each other when decompressed. Need to skip to next line in entire bitmap. i / 2 is truncated by int cast,
// so every 2 cycles (4 pixels, a full texel row) a bitmap line is skipped to the next line in texel.
int offset = decompressedStart + ((i % 2) * 8 + 3) + (decompressedLineLength * (i / 2));
destination[offset] = (byte)(source[sourceStart + i] & 0xF0); // Decompress doesn't need formatDetails as it's just reading raw.
destination[offset + 4] = (byte)(source[sourceStart + i] & 0x0F << 4);
}
// +8 skips the above alpha, otherwise it's just a BC1 RGB block
DDS_BlockHelpers.DecompressRGBBlock(source, sourceStart + 8, destination, decompressedStart, decompressedLineLength, false, isPremultiplied);
}
// TODO: Virtual/physical size. Less than 4x4 texels
#region Compressed Readers
internal static void DecompressBC1Block(byte[] source, int sourceStart, byte[] destination, int decompressedStart, int decompressedLineLength, bool isPremultiplied)
{
DDS_BlockHelpers.DecompressRGBBlock(source, sourceStart, destination, decompressedStart, decompressedLineLength, true, isPremultiplied);
}