Trying to draw rectangles in random positions
lazarus / 39-Graphics

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Prado · 2019-09-08 15:14

I'm trying to generate random points and then drawing rectangles in
those positions, after pressing a button.

The problem is that the rectangles are drawn only inside the button,
instead of the entire window.

Code of Unit:

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 const 
MAX_POINTS = 300; var  Form1: TForm1;  Points : array [0 .. MAX_POINTS
- 1] of TPoint;  {isDrawing : boolean;} implementation {$R *.lfm} {
TForm1 } procedure TForm1.FormCreate(Sender: TObject);var 
i:integer;begin  Randomize;  {isDrawing := False;}  i := 0;  while i <
MAX_POINTS do  begin    Points[i] := Point(0, 0);    i := i + 1; 
end;end; procedure TForm1.FormPaint(Sender: TObject);var 
i:integer;begin    i := 0;    while i < MAX_POINTS do      begin     
 Canvas.Pen.Color := clBlack;        Canvas.Rectangle(Points[i].x,
Points[i].y, Points[i].x + 6, Points[i].y + 6);        i := i + 1;   
 end;end; procedure TForm1.BRandomClick(Sender: TObject);var 
px:integer;  py:integer;  i:integer;begin  i := 0;  while i <
MAX_POINTS do  begin    px := random(Canvas.Width);    py :=
random(Canvas.Height);    Points[i].x := px;    Points[i].y := py;   
i := i + 1;  end;end;

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bigeno · 2019-09-08 15:29

Then don't use BRandom.Canvas

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wp · 2019-09-08 15:39

Maybe I did not set up my test program correctly, but for me there is
only a single point at the top-left corner of the form (It would be
better if you'd post a compilable project instead of a code snippet,
this avoids any misunderstandings).

I do get a form full of points when I
- use the form's width and height instead of the Canvas width/height.
In fact, I was not even aware that the canvas has a width and a
height, I always thought that it is "infinite" - maybe it is the size
of the clip rect?
- force repainting of the form by calling Invalidate at the end of the
button-click procedure.

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.Button1Click(Sender: TObject);var  px:integer;  py:integer; 
i:integer;begin  i := 0;  while i < MAX_POINTS do  begin    px :=
random(Width); //random(Canvas.Width);  <-- replaced    py :=
random(Height); //random(Canvas.Height);    Points[i].x := px;   
Points[i].y := py;    i := i + 1;  end;  Invalidate;  // <---
addedend;

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Prado · 2019-09-08 15:44

Quote from: wp on September 08, 2019, 05:39:39 pmMaybe I did not set
up my test program correctly, but for me there is only a single point
at the top-left corner of the form (It would be better if you'd post a
compilable project instead of a code snippet, this avoids any
misunderstandings).

I do get a form full of points when I
- use the form's width and height instead of the Canvas width/height.
In fact, I was not even aware that the canvas has a width and a
height, I always thought that it is "infinite" - maybe it is the size
of the clip rect?
- force repainting of the form by calling Invalidate at the end of the
button-click procedure.

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.Button1Click(Sender: TObject);var  px:integer;  py:integer; 
i:integer;begin  i := 0;  while i < MAX_POINTS do  begin    px :=
random(Width); //random(Canvas.Width);  <-- replaced    py :=
random(Height); //random(Canvas.Height);    Points[i].x := px;   
Points[i].y := py;    i := i + 1;  end;  Invalidate;  // <---
addedend;
Thanks, it works now. I forgot to mention the rectangle at the corner.