README

LCLGtk4-prototype

A GTK4 widgetset for the Lazarus Component Library (LCL) — a working, substantially complete prototype.

This repository contains the delta files to be applied on top of a Lazarus 4.4 source tree: the GTK4 widgetset itself (with its own GTK4/GDK4/GLib Pascal bindings), the LCL core changes and build registration it needs, GTK4 support units for bundled components, and the implementation audit / validation documents and example projects produced during development.

Status

Prototype — largely functional. The full Lazarus IDE (make bigide LCL_PLATFORM=gtk4) builds and runs on GTK4: the form designer, source editor (SynEdit), component palette, menus, popup menus, tooltips, common dialogs (file/color/font via native choosers), drag & drop, tray icon (StatusNotifier), and the standard/common controls have all been implemented and validated per-widget (see lazarus/LCL_WIDGETSET_IMPLEMENTATION_AUDIT.md and the lazarus/PLAN_GTK4_*_VALIDATION.md documents, each backed by an lazarus/example_gtk4_* runtime validation project).

Text input received particular attention: typed-character key events (OnKeyPress/OnUTF8KeyPress/form KeyPreview) are delivered following the Qt5 widgetset's model, and CJK input-method handling was verified with real Korean (Hangul) composition — including a local repair for an IM commit-ordering quirk of the fcitx5 GTK4 frontend that transposed a trailing space with the final committed syllable.

Environment

Developed and tested on:

Newer GTK4 releases are expected to work but have not been the primary target; a few workarounds in the widgetset are keyed to GTK 4.6-era behavior.

Known limitations

• Wayland is untested / incomplete. Development and validation were done on X11 only. In particular, popup placement (code-completion windows, hint windows) relies on X11 override_redirect; on Wayland it falls back to transient_for, which may position popups incorrectly. A proper Wayland-native popup backend has not been designed yet.
• A small number of items are inherent GTK4 backend limits (documented in the audit), e.g. TFontDialog.fdApplyButton (GtkFontChooserDialog has no apply button) and font underline/strikeout round-trips (not part of PangoFontDescription).

Layout

lazarus/lcl/interfaces/gtk4/    the widgetset + Pascal bindings (gtk4bindings/)
lazarus/lcl/                    LCL core deltas and widgetset build
                                registration (Makefile, fpmake.pp, lcl.lpk)
lazarus/components/             GTK4 support units: SynEdit (incl. CJK IME),
                                VirtualTreeView, lclextensions, printers, ideintf
lazarus/*.md                    implementation audit + per-widget validation docs
lazarus/example_gtk4_*/         runtime validation example projects
HANDOFF_NEXT_SESSION.md         development handoff notes

Building

1. Obtain a Lazarus 4.4 source tree.
2. Copy the contents of lazarus/ in this repository over it, preserving paths.
3. Build:

make bigide LCL_PLATFORM=gtk4     # full IDE (binary: ./lazarus)
make lcl    LCL_PLATFORM=gtk4     # LCL only

Applications are then built with --ws=gtk4 / LCL_PLATFORM=gtk4 as usual.

License

The widgetset and the modified files are derived from the Lazarus Component Library and follow its license: modified LGPL (LGPL with the linking exception), as published in the Lazarus source tree (COPYING.modifiedLGPL.txt).