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canvas to procedure

Posted on 1997-03-26
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Last Modified: 2010-04-04
If I have a procedure which does some drawing on a canvas, how can I tell the procedure on WHICH canvas it should draw?
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Question by:remcodek
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Accepted Solution

by:
mheacock earned 100 total points
ID: 1334962
You could pass a pointer to the canvas to the procedure...

type
  PCanvas = ^Canvas;

procedure Draw (i_pCanvas: PCanvas);
begin
   ...
   i_pCanvas^.Method(...);
   ...
end;

var
  cv: PCanvas;
begin
  pcv := @Form1.Canvas;
  Draw(pcv);
end;

Or something like this...test this out before grading me.
If you have further questions, feel free to comment.
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Author Comment

by:remcodek
ID: 1334963
It looks like an elegant solution, yet Delphi won't swallow the type-declaration. On PCanvas=^canvas it replies Undeclared Identifier:'canvas'. What did I do wrong?
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LVL 3

Expert Comment

by:mheacock
ID: 1334964
My mistake...I apologize...

type
   PCanvas = ^TCanvas;

I made a simple mistake in the declaration...should be TCanvas...not Canvas.  Sorry.
0
 
LVL 3

Expert Comment

by:mheacock
ID: 1334965
Oops...also...

  cv: PCanvas;

should be

  pcv: PCanvas;

I gotta proofread my answers being clicking the submit button.
0
 

Author Comment

by:remcodek
ID: 1334966
It's very simple:

procedure(x,y:integer;wCanvas:TCanvas);

begin
  wcanvas.pixels[x,y]:=.....
end;

works just fine.
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