Lazarus

Programming => Graphics and Multimedia => Graphics => Topic started by: pascal111 on April 21, 2021, 03:38:06 am

Title: Redrawing form
Post by: pascal111 on April 21, 2021, 03:38:06 am

I'm trying in the next piece of code to delay the drawing of line of pixels to see some motion, but I failed to make the form to redraw itself again each determined time of "delay" procedure:

Code: Pascal  [Select][+][-]

1. procedure TForm1.FormPaint(Sender: TObject);
2. var
3.  
4.   i:integer;
5.  
6. begin
7.  
8.  
9.  
10.   for i:=1 to 100 do
11.   begin
12.  
13.     canvas.Pixels[i,10]:=clblue;
14.     self.update;
15.     delay(100);
16.  
17.   end;
18.  
19.  
20.  
21.  
22.  
23. end;                
24.  

Title: Re: Redrawing form
Post by: engkin on April 21, 2021, 04:11:11 am

After delay call Application.ProcessMessages.

The correct way is to use a timer.

If you draw on the form, it will not retain the image when covered with some other window.

Title: Re: Redrawing form
Post by: engkin on April 21, 2021, 04:59:46 am

Check attached project

Title: Re: Redrawing form
Post by: pascal111 on April 21, 2021, 01:25:57 pm

I made some changes depending on attached project "simple", and it works.

Code: Pascal  [Select][+][-]

1.  
2. var
3.   Form1: TForm1;
4.   x:integer;    
5.  
6.  
7. procedure TForm1.FormPaint(Sender: TObject);
8.  
9. begin
10.  
11.  
12.      canvas.Pixels[x,10]:=clblue;
13.  
14.  
15.  
16. end;
17.  
18. procedure TForm1.Timer1Timer(Sender: TObject);
19.  
20.  
21. begin
22.  
23.   if x>=100 then
24.   exit
25.   else
26.     inc(x);
27.  
28.  
29.  
30.   Invalidate;
31.  
32.  
33. end;              
34.  

With modifying "interval" property of the timer.