Hacker's guide to WebKit/GTK+

Code layout

The GTK+ port targets the cross-platform GLib and GTK+ APIs. This means that it can be built against any of the windowing systems supported by GTK+ and Cairo without modification -- those tested so far are X11 and DirectFB. Windows should work too, possibly needing a couple of tweaks.

This means that developers adding code specific to a certain windowing system should make sure their changes are conditionally compiled only when that windowing system is available. This might be done at configure time or with a switch passed to the build system, or even just using the definitions provided by the gdk headers.

The main components of the port:

Gtk+-specific modules

• Gtk+/Gtk UI platform: ​WebCore/platform/gtk

• "Page/Gtk": ​WebCore/page/gtk

• "Loader/Gtk": ​WebCore/loader/gtk

• Public API: ​WebKit/gtk

• GtkLauncher (example application): ​WebKitTools/GtkLauncher

There may be other gtk-port related directories which have yet to be listed here.

Shared code modules

While the Gtk+ port is the primary consumer of these backends, we aim to keep them portable, avoiding even ifdef'd sections specific to the Gtk+ port:

• curl http backend: ​WebCore/platform/network/curl

• cairo graphics backend: ​WebCore/platform/graphics/cairo

• cairo graphics SVG backend: ​WebCore/platform/graphics/svg/cairo

Current tasks (July '07)

• Make things work with debugging enabled (when NDEBUG is removed, assertions are triggered right now)
• Fix animated GIF images -- consider using GdkPixbuf?
• Continue to fix the curl backend
• Start to consider consolidating the widget into a single place as the Qt port has done, and look into implementing eg. createFrame()
• Look into supporting the canvas
• Attempt to merge the Cairo code in the Win32 port -- the equivalent code is copy-and-pasted into the "Gdk" port in some places. This will help reduce code duplication but also help towards getting WebKit/Gdk/Gtk+ working on Windows

Issues known

CURL

• Review and possibly integrate the ​sand-labs CURL backend code. It has a slightly different API, so needs to be back-ported, but looks like it may be more feature-complete, able to handle redirects properly etc.
• The non zero select timeout feels bad. Make it possible to write a GSourceFunc to not poll the sockets and have a timeout: This can probably be done by integrating code from MIT/X11 licensed ​glibcurl.
• Cookie handling is completely lacking as pointed out on the mailing list
• Errors of curl need to be properly populated

Gtk

• A lot of classes are not yet implemented
• For painting we have some issues in regard to Expose Events and when WebKit will call paint.

Theming

• Consider taking code directly from Mozilla's LGPL licensed Gtk+ theming backend. They deal with a lot of corner cases which don't look fun to re-implement.
• Focus ring drawing
• Scrollbars for PlatformScrollbar will be terrible as we need to implement a HitTest but don't know where the elements of the scrollbar hide
• Native theming for text entries
• Find a way to draw a GtkComboBox, at least the button part. This is needed to implement theming of the <select> element properly.