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Timage descendent - designtime painting

Posted on 2003-11-05
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Last Modified: 2013-11-23
My component has to paint some rectangles on itself's canvas, according to some parameters.

How can my component show the rectangles even at designtime ? (like all vcl components in delphi : when you place/resize/etc the component on the form, you _see_ it , not only the contour.
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Question by:Catalin80
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7 Comments
 
LVL 5

Expert Comment

by:DeerBear
ID: 9693209
Hi,

Why do you use TImage as base class?
Wouldn't a TPaintBox have been better?

Anyway, the only "pictures" you can see at design time are
loaded files, which get displayed in the "Paint" method or the
Update one, I didn't look at the sources.

So, my guess is that you should look in the TImage class where
this happens and act accordingly.

HTH,

Andrew

P.S. As a last chance, you can always override the WM_PAINT method.
If you want a sample just let me know.
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Author Comment

by:Catalin80
ID: 9693568
If it works, give me the sample code. Thx.
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LVL 5

Accepted Solution

by:
DeerBear earned 70 total points
ID: 9693588
Hi,

This example shows a form intercepting WM_PAINT, but the
same concept applies to controls:

Type

  TMyForm = class( TForm )
   private
      procedure HandleWM_PAINT( var Mesg : TMessage );message WM_PAINT;
  end;

procedure TMyForm.HandleWM_PAINT( var Mesg : TMessage );
begin
  Inherited;// REMEMBER TO CALL INHERITED OTHERWISE THE COMPONENT WON'T WORK!!!!!!!!!!
  // Place your code here!
end;

HTH,

Andrew
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LVL 12

Expert Comment

by:andrewjb
ID: 9694687
?? There's no difference. At design time Delphi runs your code, just like at run time. If you component view OK at runtime, it should work at design time, too.

(Obviously non-visual controls don't display, but then you can't see them at runtime either)

0
 

Author Comment

by:Catalin80
ID: 9696972
@DeerBear : That works fine but : when the strech property is false, the object blinks.
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LVL 5

Expert Comment

by:DeerBear
ID: 9699508
Hi,

Use double buffering to avoid flickering.

Draw your image on a temporary bitmap and then transfer it on the
drawing surface.

HTH,

Andrew
0
 
LVL 12

Expert Comment

by:andrewjb
ID: 9700139
... or one of the vcl base classes has a 'DoubleBuffered' property, and it does it all for you.
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