Incorrect behavior of scrollbox

[simone]

Hello everyone, consider the following simple code:

Code: Pascal  [Select][+][-]

1. unit Unit1;
2.  
3. {$mode objfpc}{$H+}
4.  
5. interface
6.  
7. uses
8.   Classes, SysUtils, Forms, Controls, Graphics, Dialogs;
9.  
10. type
11.  
12.   { TForm1 }
13.  
14.   TForm1 = class(TForm)
15.     procedure FormCreate(Sender: TObject);
16.   private
17.      ScrollBox : TScrollBox;
18.   public
19.  
20.   end;
21.  
22. var
23.   Form1: TForm1;
24.  
25. implementation
26.  
27. {$R *.lfm}
28.  
29. { TForm1 }
30.  
31. procedure TForm1.FormCreate(Sender: TObject);
32. begin
33.   ScrollBox:=TScrollBox.Create(Self);
34.   ScrollBox.Parent:=Self;
35.   ScrollBox.Align:=alClient;
36.   ScrollBox.Brush.Color:=clWhite;
37.   ScrollBox.HorzScrollBar.Page:=ClientWidth;
38.   ScrollBox.HorzScrollBar.Range:=High(integer);
39.   ScrollBox.HorzScrollBar.Increment:=ClientWidth div 16;
40.   ScrollBox.VertScrollBar.Page:=ClientHeight;
41.   ScrollBox.VertScrollBar.Range:=High(integer);
42.   ScrollBox.VertScrollBar.Increment:=ClientHeight div 16;
43. end;
44.  
45. end.

Under Windows, using Lazarus 2.2.6  FPC 3.2.2 x86_64-win64-win32/win64 I have no problems.

Under Linux, using Lazarus 2.2.6 FPC 3.2.2 x86_64-linux-gtk2, when I scroll on the scrollbox, the previously invisible portion that is shown, is not white, but gray (=default color, I guess), as you can see from the attached screenshot.

Is this a bug? Do you have any tips for overcoming the problem? Thanks for the usual support.

[paweld]

use:

Code: Pascal  [Select][+][-]

1.   ScrollBox.Color:=clWhite;

instead of

Code: Pascal  [Select][+][-]

1. ScrollBox.Brush.Color:=clWhite;

[simone]

Thanks Paweld, in fact TScrollBox.Color is the property to use to set the background color of the control. I don't know why I set the brush property whith the same name.

I wonder if the different behavior between Windows and Linux is worthy of interest.

I seems that under Windows the brush color is applied to the entire surface of the control, while under Linux (gtk2), only to the surface visible at that moment.

[simone]

I tested the initial example in my post with the new Lazarus 3.0. Under Windows the behavior is now different (and more correct, in my opinion). Now:

Code: Pascal  [Select][+][-]

1. ScrollBox.Brush.Color:=clWhite;

it does not color the control surface, which appears with its default color. I haven't had a chance to try it under Linux yet.