Author: Tomas Rutkauskas

How to mirror text horizontally or vertically on a TPaintBox

Answer:

This is actually not quite straightforward. The best way to do that is to first 
paint the text onto an off-screen bitmap and then paint that bitmap on screen using 
some weird coordinate manipulations. Drop a TPaintbox on the screen and connect a 
method to its OnPaint handler. Change the handler to the code below to see how this 
works:
1   
2   procedure TForm1.PaintBox1Paint(Sender: TObject);
3   const
4     test = 'Hello world';
5   var
6     bmp: TBitmap;
7     cv: TCanvas;
8     ext: TSize;
9     r: TRect;
10  begin
11    cv := (Sender as TPaintbox).canvas;
12    ext := cv.TextExtent(test);
13    bmp := TBitmap.Create;
14    try
15      bmp.Width := ext.cx;
16      bmp.Height := ext.cy;
17      bmp.Canvas.Brush := cv.Brush;
18      bmp.Canvas.Font := cv.Font;
19      bmp.Canvas.FillRect(bmp.canvas.cliprect);
20      bmp.Canvas.TextOut(0, 0, test);
21      {draw text in normal orientation}
22      cv.Draw(0, 0, bmp);
23      r := Rect(ext.cx, 0, 0, ext.cy);
24      OffsetRect(r, 0, ext.cy);
25      {draw text horizontally mirrored}
26      cv.CopyRect(r, bmp.canvas, bmp.canvas.ClipRect);
27      r := Rect(0, ext.cy, ext.cx, 0);
28      OffsetRect(r, 0, 2 * ext.cy);
29      {draw text vertically mirrored}
30      cv.CopyRect(r, bmp.canvas, bmp.canvas.ClipRect);
31    finally
32      bmp.Free
33    end;
34  end;


The key here is to set up the target rectangle for CopyRect with left and right or top and bottom switched. Be warned, there is a slight potential that this code will cause acute indigestion for some video drivers!