static byte[] decodeMonochromeIcon(byte[] payload, CSize size)
{
int totalPixels = size.cx * size.cy;
int maskLineDwords = (size.cx + 31) / 32;
int maskStrideBytes = maskLineDwords * 4;
int bytesMask = size.cy * maskStrideBytes;
int cbHeader = Marshal.SizeOf <BITMAPINFOHEADER>();
// 8 is the color table, immediately after the header
if (payload.Length != cbHeader + (bytesMask * 2) + 8)
{
throw new ArgumentException("Size doesn't match");
}
byte[] image = new byte[totalPixels];
Span <byte> palette = stackalloc byte[4];
{
Span <uint> colorTable = stackalloc uint[2];
payload.AsSpan()
.Slice(cbHeader, 8)
.castSpan <uint>()
.CopyTo(colorTable);
ePalette pal = getPalette(colorTable);
decodePalette(pal, palette);
}
ReadOnlySpan <byte> bits = payload.AsSpan()
.Slice(cbHeader + 8, bytesMask);
ReadOnlySpan <byte> mask = payload.AsSpan()
.Slice(cbHeader + 8 + bytesMask, bytesMask);
if (0 == (size.cx % 32))
{
// No padding whatsoever
decodeMonochrome(image.AsSpan(), bits, mask, palette, totalPixels);
}
else
{
// There is some padding
Span <byte> imageSpan = image.AsSpan();
int maskBytesPerLine = (size.cx + 7) / 8;
int destOffset = 0;
int sourceOffset = 0;
for (int y = 0; y < size.cy; y++, destOffset += size.cx, sourceOffset += maskStrideBytes)
{
Span <byte> destSpan = imageSpan.Slice(destOffset, size.cx);
ReadOnlySpan <byte> lineBits = bits.Slice(sourceOffset, maskBytesPerLine);
ReadOnlySpan <byte> lineMask = mask.Slice(sourceOffset, maskBytesPerLine);
decodeMonochrome(destSpan, lineBits, lineMask, palette, size.cx);
}
}
return(image);
}
static void decodePalette(ePalette pal, Span <byte> values)
{
Debug.Assert(values.Length == 4);
// https://devblogs.microsoft.com/oldnewthing/20101018-00/?p=12513
switch (pal)
{
case ePalette.FirstBlack:
values[0] = 0; // mask 0 image 0 = black
values[1] = 0x55; // mask 0 image 1 = white
values[2] = 0xAA; // mask 1 image 0 = nop
values[3] = 0xFF; // mask 1 image 1 = invert
break;
case ePalette.FirstWhite:
values[0] = 0x55; // mask 0 image 1 = white
values[1] = 0; // mask 0 image 0 = black
values[2] = 0xFF; // mask 1 image 1 = invert
values[3] = 0xAA; // mask 1 image 0 = nop
break;
}
}
