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Remove Rectangles after painting them on "DeskTopWindow" or screen

Posted on 2009-05-04
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Medium Priority
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Last Modified: 2012-05-06
I am drawing a rectangle around buttons in my application by using this funny method below.
The problem is that after I draw these rectangles I cannot clear them (unless I 'drag' my form off the screen and back on again).

I have tried calling canvas.repaint / canvas.refresh but it doesn't work.
procedure BorderMyControl(DaControl : TControl);
var
  C : TCanvas;
  DeskTopWindowDC : HDC;
begin
  C := TCanvas.Create;
  with C do
  try
    DeskTopWindowDC := GetWindowDC(GetDeskTopWindow);
      try
        Handle := DeskTopWindowDC;
        Brush.Style := bsClear;
        Pen.Width := 3;
        Rectangle(Rect(DaControl.Left - 2, DaControl.Top - 2, DaControl.Left + DaControl.Width + 2, DaControl.Top + DaControl.Height + 2));
      finally
        ReleaseDC(GetDesktopWindow, DeskTopWindowDC);
    end;
  finally
    Free;
  end;
end;

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Question by:rfwoolf
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4 Comments
 
LVL 38

Assisted Solution

by:Geert Gruwez
Geert Gruwez earned 100 total points
ID: 24302596
it would be solved with a bevel too
0
 
LVL 12

Accepted Solution

by:
Hypo earned 1900 total points
ID: 24302830
Isn't your problem that you paint it on the Desktop DC, and not on your controls Parent DC? I belive that's what causes your problem. When I ran your exapmle, the border was not painted at the correct locations, but anyway, I got the idea of what you were talking about. After I changed the DC to be the parent of the Control instead, then I could call Repaint on the parent, and the border was removed.

    DeskTopWindowDC := GetWindowDC(DaControl.Parent.Handle);

regards
Hypo
0
 
LVL 13

Author Comment

by:rfwoolf
ID: 24307171
I'm satisfied at the answer but I'm sure I did try and refresh the desktop and failed. One of the problems I'm sure I'm running into is that the form's canvas includes the header, so if I draw a rectangle starting at 0,0 on the form it will appear on the title bar. Anyway, let's see if we can address this in a separate question.
0
 
LVL 13

Author Comment

by:rfwoolf
ID: 24307189
Sorry I wasn't clear above, what I'm trying to say Hypo is this:
Your solution is a great workaround for my particular problem, but,
what if I did want to draw on the desktop, and what if I did have trouble removing the squares on the desktop window handle? Your answer doesn't address this.
Anyways, I would prefer to draw on the form instead of the desktop so let's just move on :p

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