Author: Tomas Rutkauskas

How to XOR a font on a bitmap canvas

Answer:

Write the text to a (temporary) bitmap and copyrect that to the image:
1   
2   procedure XORText(sheet: TCanvas; x, y: Integer; text: string);
3   var
4     bmp: TBitmap;
5     r1, r2: TRect;
6   begin
7     bmp := TBitmap.create;
8     try
9       with sheet do
10      begin
11        bmp.Width := textWidth(text);
12        bmp.height := textheight(text);
13        r1 := rect(0, 0, bmp.Width, bmp.Height);
14        r2 := Rect(x, y, x + bmp.Width, y + bmp.Height);
15        bmp.canvas.font.assign(font);
16        bmp.canvas.brush.color := clBlack;
17        bmp.Canvas.fillrect(r1);
18        bmp.canvas.brush.style := bsClear;
19        bmp.canvas.textout(0, 0, text);
20        copymode := cmSrcInvert;
21        copyrect(r2, bmp.canvas, r1);
22      end;
23    finally
24      bmp.free;
25    end;
26  end;