Bitmap.Save to save an icon actually saves a .png

Question

I need to write a program that will generate 108 combinaisons of icons (standard windows .ico files) based on a tileset image.

I use the class System.Drawing.Bitmap

Answer 1

I made a quick-and-dirty workaround myself, I post it here for the record (it might help someone that need a quick solution, like me).

I won't accept this as the correct answer, it's not an actual icon writer. It just write a 32bits ARGB bitmap into an ico file, using PNG format (works on Vista or later)

It is based on the ICO file format article from Wikipedia, and some fails and retry.

void SaveAsIcon(Bitmap SourceBitmap, string FilePath)
{
    FileStream FS = new FileStream(FilePath, FileMode.Create);
    // ICO header
    FS.WriteByte(0); FS.WriteByte(0);
    FS.WriteByte(1); FS.WriteByte(0);
    FS.WriteByte(1); FS.WriteByte(0);

    // Image size
    FS.WriteByte((byte)SourceBitmap.Width);
    FS.WriteByte((byte)SourceBitmap.Height);
    // Palette
    FS.WriteByte(0);
    // Reserved
    FS.WriteByte(0);
    // Number of color planes
    FS.WriteByte(0); FS.WriteByte(0);
    // Bits per pixel
    FS.WriteByte(32); FS.WriteByte(0);

    // Data size, will be written after the data
    FS.WriteByte(0);
    FS.WriteByte(0);
    FS.WriteByte(0);
    FS.WriteByte(0);

    // Offset to image data, fixed at 22
    FS.WriteByte(22);
    FS.WriteByte(0);
    FS.WriteByte(0);
    FS.WriteByte(0);

    // Writing actual data
    SourceBitmap.Save(FS, ImageFormat.Png);

    // Getting data length (file length minus header)
    long Len = FS.Length - 22;

    // Write it in the correct place
    FS.Seek(14, SeekOrigin.Begin);
    FS.WriteByte((byte)Len);
    FS.WriteByte((byte)(Len >> 8));

    FS.Close();
}