CrystalMpq.DataFormats.ArgbColor.CopyWithAlpha C# (CSharp) Method

        internal static unsafe void CopyWithAlpha(ArgbColor* destination, ArgbColor* source, byte alpha)
        {
            destination->B = source->B;
            destination->G = source->G;
            destination->R = source->R;
            destination->A = alpha;
        }

        private unsafe void CopyToArgbAlpha4(SurfaceData surfaceData)
        {
            // Use a precalculated alpha table for very fast conversions.
            var alphaTable = stackalloc byte[16];

            for (int i = 0; i < 16; i++)
                alphaTable[i] = (byte)(i * (255 * 2185) >> 15);                                      // x / 15 = x * 2185 >> 15 (for 0 ≤ x ≤ 15 * 255)

            fixed(byte *dataPointer = data)
            fixed(ArgbColor * palettePointer = palette)
            {
                byte *destinationRowPointer = (byte *)surfaceData.DataPointer;
                byte *sourceColorPointer    = dataPointer;
                byte *sourceAlphaPointer    = dataPointer + Width * Height;
                byte  alphaData             = 0;
                bool  alphaState            = false;

                for (int i = Height; i-- != 0; destinationRowPointer += surfaceData.Stride)
                {
                    ArgbColor *destinationPointer = (ArgbColor *)destinationRowPointer;

                    for (int j = Width; j-- != 0;)
                    {
                        ArgbColor.CopyWithAlpha(destinationPointer++, palettePointer + *sourceColorPointer++, alphaTable[(alphaState = !alphaState) ? (alphaData = *sourceAlphaPointer++) & 0xF : alphaData >> 4]);
                    }
                }
            }
        }