private static byte[] EncodeIndexedBitmap(ParseContext context, BitmapEncoding encoding, Dialect dialect, IcoFrame source)
{
var numBits = BmpUtil.GetBitDepthForPixelFormat(encoding);
var colorTable = BuildColorTable(1u << numBits, context, source);
if (colorTable == null)
{
context.LastEncodeError = IcoErrorCode.TooManyColorsForBitDepth;
return(null);
}
var writer = new ByteWriter(ByteOrder.LittleEndian);
EncodeBitmapHeader(source, dialect, encoding, colorTable, writer, out var offsetToImageSize);
var reverseTable = new Dictionary <Rgba32, int>();
for (var i = 0; i < colorTable.Length; i++)
{
if (!reverseTable.ContainsKey(colorTable[i]))
{
reverseTable.Add(colorTable[i], i);
}
}
var offsetToData = (uint)writer.Data.Count;
var padding = writer.Data.Count % 4;
for (var y = source.CookedData.Height - 1; y >= 0; y--)
{
var bits = new BitWriter(writer);
for (var x = 0; x < source.CookedData.Width; x++)
{
var color = source.CookedData[x, y];
if (source.Mask[x, y])
{
switch (context.MaskedImagePixelEmitOptions)
{
case StrictnessPolicy.Compliant:
color = new Rgba32(0, 0, 0, 255);
break;
case StrictnessPolicy.PreserveSource:
// Pass through whatever the original pixel was.
break;
case StrictnessPolicy.Loose:
color = colorTable.First();
break;
}
}
color.A = 255;
var index = reverseTable[color];
bits.AddBits((uint)numBits, (byte)index);
}
while ((writer.Data.Count % 4) != padding)
{
writer.AddUint8(0);
}
}
return(FinalizeBitmap(source, encoding, dialect, writer, offsetToData, offsetToImageSize));
}