trying to draw over a timage

Question

I have written a simple program (using Delphi XE7); it has a TImage and a TPaintBox (partially over the Timage). In the FormPaint procedure I am calling "BringToFront" and then drawing a (filled) rectangle. The rectangle appears under the image.

procedure TForm1.FormPaint(Sender: TObject);
begin
 with paintbox1 do
   begin
     BringToFront;
     canvas.Rectangle(0,0,width-1,height-1);
   end;
end;

This is a image of the program window:

I expected the rectangle to be over the image. What am I doing wrong? :)

Alex R. · Accepted Answer · 2020-04-19T20:33:33.683

3

You are not using PaintBox correctly. PaintBox has its own event for drawing. You should use TPaintBox.OnPaint instead of TForm.OnPaint and result will be as you wrote.

~~You can also draw directly on the picture. In this case, used event TForm.OnPaint~~.

You can also draw directly on the image after its picture has changed (for example, after loading). It works if used TBitmap graphics.

procedure TForm1.button1click(Sender: TObject);
begin
  image1.LoadFromFile('c:\temp\1.bmp')
  image1.canvas.Rectangle(0,0,100,100);
end;

edited Apr 19 '20 at 20:33

answered Apr 19 '20 at 06:10

Alex R.

266
2
9

Thanks very much! Silly mistake. :) – Steve Peter Apr 19 '20 at 06:24
The `TForm.OnPaint` event is the wrong place to draw on a `TImage`, too. `TImage` holds a `TPicture` and handles its own drawing events to render that picture. – Remy Lebeau Apr 19 '20 at 19:25
I agree that it is wrong to use `TForm.OnPaint`. But `TImage` and `TPicture` has no events for drawing. I correct answer. – Alex R. Apr 19 '20 at 20:34

trying to draw over a timage

1 Answers1