I am writing a program that a part renders a bitmap font in CP437.
In a function that renders the text with I want to be able to check whether a char
is available in CP437 before the encoding conversion, like:
public static void DrawCharacter(this Graphics g, char c)
{
if (char_exist_in_encoding(Encoding.GetEncoding(437), c) {
byte[] src = Encoding.Unicode.GetBytes(c.ToString());
byte[] dest = Encoding.Convert(Encoding.Unicode, Encoding.GetEncoding(437), src);
DrawCharacter(g, dest[0]); // Call the void(this Graphics, byte) overload
}
}
Without the check, any characters outside CP437 will result in a '?'
(63, 0x3F). I want to hide any invalid characters completely. Is there an implementation of char_exist_in_encoding
other than the following stupid approach?
private static bool char_exist_in_encoding(Encoding e, char c)
{
if (c == '?')
return true;
byte[] src = Encoding.Unicode.GetBytes(c.ToString());
byte[] dest = Encoding.Convert(Encoding.Unicode, e, src);
if (dest[0] == 0x3F)
return false;
return true;
}
Perhaps not very relevant, but the bitmap is created like this:
Bitmap b = new Bitmap(256 * 8, 16);
Graphics g = Graphics.FromImage(b);
g.TextRenderingHint = System.Drawing.Text.TextRenderingHint.SingleBitPerPixelGridFit;
Font f = new Font("Whatever 8x16 bitmap font", 16, GraphicsUnit.Pixel);
for (byte i = 0; i < 255; i++)
{
byte[] arr = Encoding.Convert(Encoding.GetEncoding(437), Encoding.Unicode, new byte[] { i });
char c = Encoding.Unicode.GetChars(arr)[0];
g.DrawString(c.ToString(), f, Brushes.Black, i * 8 - 3, 0); // Don't know why it needs a 3px offset
}
b.Save(@"D:\chars.png");
Thanks to Vlad, after a bit research on EncoderFallback
I finally saw an example in MSDN
My working (perhaps temporary working) code is:
public static void DrawCharacter(this Graphics g, char c)
{
byte[] src = Encoding.Unicode.GetBytes(c.ToString());
byte[] dest = Encoding.Convert(Encoding.Unicode, Encoding.GetEncoding(437, new EncoderReplacementFallback(" "), new DecoderReplacementFallback(" ")), src);
DrawCharacter(g, dest[0]);
}
It replace invalid characters to a space " "
.
P.S. I originally used an empty string
""
as the replacement but finally I decided to use the space character, because it looks cleaner.
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