title: How to draw over a fresh copy of Timage with Canvas.CopyRect()
body: <p>I have a code to draw a moving line over timage, and I want the previous old line always to disappear, but this code makes all lines to appears there for ever...  When I enable DoubleBuffering to form, the code below works OK  but the background bitmap located in myimg  does not show at all.</p>
  
  <pre><code>  Fbitmap.Canvas.Pen.Color:=clRed;
    Fbitmap.Canvas.Pen.Width:=2;
    Fbitmap.Canvas.MoveTo(Xo,Yo);
    Fbitmap.Canvas.LineTo(Xs,Ys);
    myimg.Canvas.CopyRect(Rect(0, 0, Width, Height), FBitmap.Canvas, Rect(0, 0, Width, Height));
  </code></pre>