Hi,

the code below is part of a program to draw the Mandelbrot-set. It works, if the canvas is small (stamp-size). However, if the size is increased to 800x800, the middle 1/3 of the image is replaced by a vertical grey bar. Any ideas?

Thanks in advance

Engelbert

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procedure TForm_MandelbrotSet.B_DrawClick(Sender: TObject);
var dp, dq : real;
      np, nq : word;
 procedure Iterate (np, nq : word);
 var p, q, x, y, x_old : real;
       k                       : word;
 begin
   p := P_min + np * dp;
   q := Q_min + nq * dq;
   k := 0;
   x := 0;
   y := 0;
   repeat
     x_old := x;
     x := x*x - y*y + p;
     y := 2 * x_old * y + q;
     inc(k);
   until (x*x + y*y > r_max) or (k = k_max);
   if k = k_max then k := 0;
   PB_Drawing.Canvas.Pixels[np, PB_Drawing.Height-nq] := k;
 end;
begin
 dp := (P_max - P_min) / PB_Drawing.Width;
 dq := (Q_max - Q_min) / PB_Drawing.Height;
 for np := 1 to PB_Drawing.Width do
 for nq := 1 to PB_Drawing.Height do
 Iterate(np, nq);
end;
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Hi, the code below is part of a program to draw the Mandelbrot-set. It works, if the canvas is small (stamp-size). However, if the size is increased to 800x800, the middle 1/3 of the image is replaced by a vertical grey bar. Any ideas?

What is PB_Drawing?
If it is a TImage you have to resize it yourself. The Picture is not resized automatically.

PB_drawing.Picture.Width:=PB_drawing.Width;
PB_drawing.Picture.Height:=PB_drawing.Height;

Mattias

Engelbert Buxbaum wrote

Hi, the code below is part of a program to draw the Mandelbrot-set. It works, if the canvas is small (stamp-size). However, if the size is increased to 800x800, the middle 1/3 of the image is replaced by a vertical grey bar. Any ideas?

What widgetset / OS do you use?

Maybe see: http://bugs.freepascal.org/view.php?id=15822

Vincent

Engelbert Buxbaum wrote

Hi, the code below is part of a program to draw the Mandelbrot-set. It works, if the canvas is small (stamp-size). However, if the size is increased to 800x800, the middle 1/3 of the image is replaced by a vertical grey bar. Any ideas?

*Sound* *like* a known bug in certain MS-Windows versions.

They ignore SetPixel for all x coordinates with bit 8=1

you can setpixels from 0 to 255, 512, to 767, 1024 to ....

It doesn't matter in which language, you program, the bug is in windows itself

Martin

AFAIK it is fixed in trunk.

Marc