[Lazarus] Drawing problem in Linux based on GTK2/QT4

[GroundCAD Algeria]

Hi
I developed a 2D CAD ( GroundCAD  www.groundcad.com ) software using
Lazarus ( working with LCL only ).

In windows, the software is stable in the processing and in the drawing.

I ported my project to linux 32 (mint 17.2) using Lazarus 1.4.2 configured
on GTK2, When I zoomed In my drawing in the maximum scale (range of 1mm ) I
get a duplicated lines (the drawing of entities outside the screen system).

In my code, Before the drawing, I check if entity position is inside the
canvas and I have the same problem.

As solution, I tested a custom method to draw a line,using Bresenham's line
algorithm. and I add a check In the pixel position (X,Y) must be inside the
canvas ( 0 --> width ; 0 --> Height ) before the drawing.

The result of this method is good and correct but slow. If I apply a
maximum scale in my drawing .

I have 2 questions
- In Linux GTK2/QT4, where is the problem if I apply a maximum scale ?
- Can I add a check on pixel position inside the canvas methods
(line,polylin,polygon,rectangle,ellipse ...)

Best regards
Naoum Mabkhout



Test drawing line Unit :
procedure TCadLine.DrawLine(workspace:TCanvas);
VAR
     a,b          :  INTEGER;
     d            :  INTEGER;
     diag_inc     :  INTEGER;
     dx_diag      :  INTEGER;
     dx_nondiag   :  INTEGER;
     dy_diag      :  INTEGER;
     dy_nondiag   :  INTEGER;
     i            :  INTEGER;
     nondiag_inc  :  INTEGER;
     swap         :  INTEGER;
     X,Y          :  INTEGER;  // Pixel position

BEGIN

if self.IsCreated=true then
BEGIN
  if plan.ApplyZoomOrPan=true then
  begin
      self.XstartScreen := plan.GetXscreenFromX(self.Xstart,workspace);
      self.YstartScreen := plan.GetYscreenFromY(self.Ystart,workspace);
      self.ZstartScreen := round(self.Zstart);
      self.XendScreen   := plan.GetXscreenFromX(self.Xend,workspace);
      self.YendScreen   := plan.GetYscreenFromY(self.Yend,workspace);
      self.ZendScreen   := round(self.Zend);
      self.XmidScreen   := plan.GetXscreenFromX(self.GetMidX,workspace);
      self.YmidScreen   := plan.GetYscreenFromY(self.GetMidY,workspace);
      self.ZmidScreen   := round(self.GetMidZ);
  end;

   X := self.XstartScreen;
   Y := self.YstartScreen;

   a := self.XendScreen - self.XstartScreen;
   b := self.YendScreen - self.YstartScreen;

   IF   a < 0 THEN
   BEGIN
     a := -a;
     dx_diag := -1
   END
   ELSE
     dx_diag := 1;

   IF   b < 0 THEN
   BEGIN
     b := -b;
     dy_diag := -1
   END
   ELSE
     dy_diag := 1;

   IF   a < b THEN
   BEGIN
     swap := a;
     a := b;
     b := swap;
     dx_nondiag := 0;
     dy_nondiag := dy_diag
   END
   ELSE
   BEGIN
     dx_nondiag := dx_diag;
     dy_nondiag := 0
   END;
   d := b + b - a;
   nondiag_inc := b + b;
   diag_inc    := b + b - a - a;

   FOR i := 0 TO a DO
   BEGIN

       // Must Add a check if pixel position X,Y
       // inside the canvas before draw the pixel

       if    (X>=0)  and (X<= workspace.Width )
       and (Y>=0) and (Y<= workspace.Height ) then
                     workspace.Pixels[X,Y] := self.Color;

     IF   d < 0 THEN
     BEGIN
       x := x + dx_nondiag;
       y := y + dy_nondiag;
       d := d + nondiag_inc
     END
     ELSE
     BEGIN
       x := x + dx_diag;
       y := y + dy_diag;
       d := d + diag_inc
     END
   END;

 END;
END;
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.lazarus-ide.org/pipermail/lazarus/attachments/20150904/7e5d623b/attachment-0002.html>