Graphical user interface toolkit in Object Pascal
fpGUI, the Free Pascal GUI toolkit, is a cross-platform graphical user interface toolkit developed by Graeme Geldenhuys. fpGUI is open source and free software, licensed under a Modified LGPL license. The toolkit has been implemented using the Free Pascal compiler, meaning it is written in the Object Pascal language.
fpGUI consists only of graphical widgets or components, and a cross-platform 2D drawing library. It doesn't implement database layers, 3D graphics, XML parsers etc. It also doesn't rely on any huge third party libraries like GTK or Qt. All the extras come straight from what is available with the Free Pascal Component Library (FCL) which comes standard with the Free Pascal compiler.
History.
The first version of fpGUI was written by Sebastian Günther back in 2000. The project was then abandoned in 2002. fpGUI was a successor to an earlier OO GTK wrapper, fpGTK, and was pretty much a fresh start to allow multiple (backend) widgetsets, most notably win32. The toolkit was used for some internal FPC tooling (e.g. the fpdoc editor), but there were still a lot of open issues before the toolkit could be truly useful and used in real life applications by end-users. Most of these tools where migrated to the maturing Lazarus in the 2004-2006 timeframe.
Graeme Geldenhuys revived the toolkit in mid-2006 where Sebastian left off. He continued developing the toolkit for the next year. Merging three sub-projects (fpGFX, fpIMG and fpGUI) into a single project fpGUI. Graeme extended the number of components and amount of backend graphics layer, and improved the overall toolkit. The supported platforms at that stage was Linux and FreeBSD via X11 and Microsoft Windows via GDI. After a few months Felipe Monteiro de Carvalho joined the development team adding support for Windows Mobile devices and extending the graphics support and design. Felipe also started working on Mac OS X support via Carbon.
At the beginning of June 2007 Graeme found some major design issues in the source base. This prevented fpGUI from being truly useful in real applications. After numerous prototypes the fpGUI project was completely rewritten. Past experience helped a lot and new design ideas were implemented. The code base ended up being much simpler with a cleaner design. One of the major changes was that all widgets were now based on a multi-handle (windowed) design. Each widget now has a window handle. Other GUI toolkits that follow a similar design are GTK, Xt and FLTK to name a few. GUI toolkits that follow the opposite design are toolkits like the latest Qt and MSEgui.
Example program.
The following program shows a single window with a "Quit" button in the bottom right. On the canvas (background) of the window it paints all the standard built-in images used with fpGUI.
program stdimglist;
uses
 Classes, SysUtils,
 fpg_base, fpg_main, fpg_form, fpg_imgfmt_bmp, fpg_button;
type
 TMainForm = class(TfpgForm)
 private
 btnClose: TfpgButton;
 procedure btnCloseClick(Sender: TObject);
 protected
 procedure HandlePaint; override;
 public
 constructor Create(aowner: TComponent); override;
 procedure AfterCreate; override;
 end;
procedure TMainForm.AfterCreate;
begin
 SetPosition(100,100,700,500);
 WindowTitle := 'fpGUI Standard Image Listing';
 // Place button in bottom right corner.
 btnClose := CreateButton(self, Width-90, Height-35, 75, 'Quit', [Tag]);
 btnClose.ImageName := 'stdimg.quit';
 btnClose.Anchors := [anRight, anBottom];
end;
procedure TMainForm.btnCloseClick(Sender: TObject);
begin
 Close;
end;
procedure TMainForm.HandlePaint;
var
 n: integer;
 x: TfpgCoord;
 y: TfpgCoord;
 sl: TStringList;
 img: TfpgImage;
begin
 Canvas.BeginDraw; // begin double buffering
 inherited HandlePaint;
 sl := TStringList.Create;
 x := 8;
 y := 8;
 fpgImages.ListImages(sl);
 for n := 0 to sl.Count-1 do
 begin
 Canvas.DrawString(x, y, sl[n]+':');
 img := TfpgImage(sl.Objects[n]);
 if img ; ; nil then
 Canvas.DrawImage(x+130, y, img);
 inc(y, img.Height+8);
 if y ; Height-32 then // largest images are 32 in height
 begin
 inc(x, 200);
 y := 8;
 end;
 end;
 Canvas.EndDraw;
 sl.Free;
end;
constructor TMainForm.Create(aowner: TComponent);
begin
 inherited Create(aowner);
(* PRIOR TO v1.4:
 // Place button in bottom right corner.
 btnClose := CreateButton(self, Width-90, Height-35, 75, 'Quit', [Tag]);
 btnClose.ImageName := 'stdimg.quit';
 btnClose.Anchors := [anRight, anBottom];
end;
procedure MainProc;
var
 frm : TMainForm;
begin
 fpgApplication.Initialize;
 frm := TMainForm.Create(nil);
 try
 frm.Show;
 fpgApplication.Run;
 finally
 frm.Free;
 end;
end;
begin
 MainProc;
end.
Here is a screenshot of the above program when run under Linux.
Licensing.
fpGUI is statically linked into programs and is licensed using a modified version of LGPL specially designed to allow static linking to proprietary programs. The only code you need to make available are any changes you made to the fpGUI toolkit - nothing more.
References.
 ;templatestyles src="Reflist/styles.css" / ;