Prototype for custom drawing in the timeline

[Ichthyostega]

The Timeline widget needs to be rewritten to work with GTK-3.
Use this as an opportunity to implement a prototype for custom drawing of regions, tracks and marker overlays in the timelines.

• find a way to organise drawing code in the context of a recursive widget implementation
• pick a suitable base GTK widget, which supports both
  • invoking a custom drawing function
  • attach nested sub-widgets at fixed positions

[Ichthyostega]

During the last years, this prototype has been built step by step, interwoven with a complete reorganisation of the GUI top-level context, and a rework of the Timeline UI.

• we use the Gtk::Layout widget as foundation
• this widget is both a container widget, while also offering a canvas for custom drawing
• this allows to attach regular widgets with all features like theming, automatic layout, event handling and i18n
• a special solution was devised to pick up CSS style information from a virtual widget path and use this to control our custom drawing code
• we can now document a basic Timeline display with main tracks, ruler tracks, nested tracks and attached clips, styled by CSS rules and fully integrated with the desktop theme

[Undercover Agent]

Migration MasterTickets ⟼ Subtickets-plugin