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fpGUI is a cross-platform GUI toolkit written entirely in Object Pascal using the Free Pascal Compiler. It provides a custom-drawn widget set that renders consistently across all supported platforms, with no external widget toolkit dependencies. All rendering is done through the built-in AggPas hybrid canvas, which uses platform APIs (X11, GDI, Cocoa) for window management and input while delivering fully platform-independent, pixel-perfect output via software rasterisation.

FPC Version License

1. Features

  • Cross-platform: Linux (X11), Windows (GDI), macOS (Cocoa), FreeBSD, OpenSolaris

  • AggPas hybrid canvas: Platform-independent rendering via 100% Object Pascal software rasteriser

  • No external dependencies: No GTK, Qt, or other widget toolkit required

  • Custom-drawn widgets: Consistent look and feel across all platforms

  • Themeable: Multiple built-in styles including plastic and dark themes

  • Layout managers: MigLayout (ported from Java), FlowLayout, and BorderLayout

  • Fluent constraint API: LC, AC, and CC classes for concise layout definitions

  • Rich widget set: Buttons, edits, grids, treeviews, listviews, menus, tabs, scrollbars, and more

  • Visual form designer: UI Designer for rapid form creation

  • PDF reporting engine: Built-in report generation with print preview

  • Drag and drop: OS-independent DND support between applications and widgets

  • Unicode support: Full Unicode text input and rendering

  • Documentation viewer: DocView application for viewing INF/IPF help files

2. Project Structure

Directory Description

framework/src/main/pascal/

Core fpGUI framework source

framework/src/test/pascal/

Unit tests

uidesigner/

Visual UI Designer application

docview/

Documentation viewer (INF/IPF file viewer)

examples/

Example applications and widget demos

extras/

Third-party contributed components

3. Building

3.1. Prerequisites

3.1.1. Linux / FreeBSD

Install the X11 development libraries:

sudo apt-get install libx11-dev libxft-dev libxext-dev

libxext-dev provides libXext.so, which the X11 backend links against for the XSync extension. Distributions that ship only the runtime libXext.so.6 will fail at link time with cannot find -lXext.

3.1.2. AggPas Canvas

fpGUI uses the AggPas hybrid canvas on all platforms. Ensure the Liberation Sans font is installed on Linux/FreeBSD. On Windows, the canvas uses Arial (included with the OS) via the native Win32 TrueType font engine — no external DLL required.

3.2. Compiling the Framework

Using PasBuild from the project root:

# Linux / FreeBSD
pasbuild compile -m fpgui-framework -p unix
pasbuild compile -m fpgui-framework -p unix,debug   # with debug symbols
# Windows
pasbuild compile -m fpgui-framework -p windows
pasbuild compile -m fpgui-framework -p windows,debug  # with debug symbols

3.3. Running Tests

pasbuild test

3.4. Compiling Everything

To compile the entire project (framework, applications, examples, and tools):

pasbuild compile -p unix
pasbuild compile -p windows

3.5. Compiling Individual Applications

To compile a specific module:

# DocView
pasbuild compile -m fpgui-docview -p unix
# UI Designer
pasbuild compile -m fpgui-uidesigner -p unix
# All examples at once
pasbuild compile -m fpgui-examples -p unix
# A specific example (e.g. MigLayout demo)
pasbuild compile -m examples-gui-lmmig -p unix

4. Quick Start

program ContactForm;
{$mode objfpc}{$H+}
uses
  fpg_base, fpg_main, fpg_form, fpg_label, fpg_edit, fpg_button,
  fpg_miglayout, fpg_mig_lc, fpg_mig_cc;
type
  TMainForm = class(TfpgForm)
  public
    procedure AfterCreate; override;
  end;
procedure TMainForm.AfterCreate;
var
  mig: TfpgMigLayoutManager;
  lbl: TfpgLabel;
  edt: TfpgEdit;
  btn: TfpgButton;
begin
  inherited AfterCreate;
  WindowTitle := 'Contact Form';
  Width := 400;
  Height := 200;
  // Create a 2-column MigLayout grid
  mig := TfpgMigLayoutManager.Create;
  mig.LC.SetWrapAfter(2);
  LayoutManager := mig;
  // Row 1: Name
  lbl := TfpgLabel.Create(Self);
  lbl.Text := 'Name:';
  mig.AddLayoutComponent(lbl, TfpgMigCC.Create());
  edt := TfpgEdit.Create(Self);
  edt.PreferredSize := fpgSize(200, 24);
  mig.AddLayoutComponent(edt, TfpgMigCC.Create().GrowX());
  // Row 2: Email
  lbl := TfpgLabel.Create(Self);
  lbl.Text := 'Email:';
  mig.AddLayoutComponent(lbl, TfpgMigCC.Create());
  edt := TfpgEdit.Create(Self);
  edt.PreferredSize := fpgSize(200, 24);
  mig.AddLayoutComponent(edt, TfpgMigCC.Create().GrowX());
  // Row 3: Buttons spanning both columns
  btn := TfpgButton.Create(Self);
  btn.Text := 'OK';
  btn.PreferredSize := fpgSize(80, 24);
  mig.AddLayoutComponent(btn, TfpgMigCC.Create().SpanX.Split(2).Tag('ok'));
  btn := TfpgButton.Create(Self);
  btn.Text := 'Cancel';
  btn.PreferredSize := fpgSize(80, 24);
  mig.AddLayoutComponent(btn, TfpgMigCC.Create().Tag('cancel'));
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.

5. Licensing

The fpGUI framework is distributed under the LGPL-2.1 with a static linking exception (Modified LGPL), the same license model used by the Free Pascal RTL and Lazarus LCL. This permits use in both open-source and proprietary applications without requiring the application source to be published.

See license.ModifiedLGPL.txt and license.LGPL2.txt for full details.

Component License

Framework (framework/)

Modified LGPL

UI Designer (uidesigner/)

Modified LGPL

DocView (docview/)

GPLv2

Examples (examples/)

GPLv2

Extras (extras/)

Various (see specific directories)

6. Contributing

Contributions are welcome. Please submit pull requests against the develop branch.

7. Links

Read the original on github.com ↗