Canvas.Rectangle wrong [Solved]
lazarus / 39-Graphics

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lainz · 2019-12-21 12:12

Hi, try this code on Windows:

Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i procedure
TForm1.PaintBox1Paint(Sender: TObject);begin 
PaintBox1.Canvas.Pen.Width:=2;  PaintBox1.Canvas.Rectangle(0, 0,
PaintBox1.Width, PaintBox1.Height);end;
You will notice that the top and left borders has 1px wide only,
instead of 2.

Also try this:

Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i procedure
TForm1.PaintBox1Paint(Sender: TObject);begin 
PaintBox1.Canvas.Pen.Width:=2;  PaintBox1.Canvas.Rectangle(1, 1,
PaintBox1.Width, PaintBox1.Height);end;
This fixes the width, but there are 2 missing pixels, at the top left
and top right.

Tested on Windows 10.

There are more properties I need to set to get a proper drawing? (I
mean 2px width in each border, without missing pixels).

Thanks 

Edit: On Delphi I get the first test the same (missing 1px at left and
top), and the second is without missing pixels (the output is the
desired).

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winni · 2019-12-21 12:26

Hi!

This error was already there in Delphi 1. In Lazarus with gtk you get
the same result.

The problem is that it should be the same result for all 4 sides.

Either: (0,0,width,height) draws 1 pixel - the other pixel is
"outside" the component
Or : this draws 2 pixel per line -  then you run in trouble in the
very center of the paintbox.

Winni

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lainz · 2019-12-21 12:36

Ok thanks.

Problem solved, just adding these properties:

Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i
PaintBox1.Canvas.Pen.Width:=2; // or any width, the settings will
respectPaintBox1.Canvas.Pen.JoinStyle:=pjsMiter;// remove rounded
bordersPaintBox1.Canvas.Pen.Style:=psInsideframe; // draw border
inside rectanglePaintBox1.Canvas.Rectangle(0, 0, PaintBox1.Width,
PaintBox1.Height);
If I not set pjsMiter it draw rounded borders. If I not set
psInsideframe it draws the line centered in the border (half inside,
half outside). Setting these two properties solves the problem, I get
perfect borders for any pen width values.