Component cannot draw outside of paint method ?
lazarus / 39-Graphics

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dpsoftware · 2010-06-06 07:11

I have a component for a ruler based on a TGraphocControl. It draws
the ruler fine in the paint method. But in response to a mouse
movement, it calls a routine to add a vertical line across the ruler.
It seems that the moveto and lineto commands are not working outside
the paint method although changes in penwidth remain for the next
paint.

Anyone know if this is a bug or a restriction and how to get around it
?

Component worked fine on Delphi 6 and has been converted.

TRuler = class(TGraphicControl)
..
..

procedure TRuler.Paint;  { works fine } 

begin
  with canvas do    
  begin
    moveto(x,y)
    lineto(x2,y2)
  ..
  ..
end; 

procedure TRuler.setMarkerPos(iValue: Integer);  { no effect but its
being called }

begin
  with canvas do    
  begin
    moveto(x,y)
    lineto(x2,y2)
  ..
  ..
end;

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theo · 2010-06-06 07:50

Quote from: dpsoftware on June 06, 2010, 09:11:22 amAnyone know if
this is a bug or a restriction
It's a restriction afaik. On certain systems, painting outside the
OnPaint event handler won't work at all.

Quote from: dpsoftware on June 06, 2010, 09:11:22 am.. and how to get
around it ?
Paint in OnPaint, or Paint on a buffer (Bitmap) which you copy to the
screen in OnPaint.

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dpsoftware · 2010-06-06 11:43

Thanks, I just did everything in paint and it works fine. The original
didn't redraw after every change in mouse position but used an xor
draw to update the position marker.  It doesn't seem to be a problem
redrawing the entire ruler.