Features/Optimize TreeViews

Summary
Gonzalo Odiard and Manuel Quiñones did a hackaton to find out why the lists that contain icons are so slow. The affected views in Sugar are the Journal list and the activities list. This feature is about improving the TreeView performance.

Owner

 * Name: Manuel Quiñones
 * Name: Gonzalo Odiard

Current status

 * Targeted release: 0.104
 * Last updated: Nov 17, 2014
 * Percentage of completion: 90%

Findings

 * The source of the performance issues is Sugar CellRendererIcon, a treeview without it works ok. https://github.com/sugarlabs/sugar-toolkit-gtk3/blob/master/src/sugar3/graphics/icon.py#L781

In particular, a CellRenderer is not a Widget, then do not have event to know when the mouse interact, then needed attach to the events on the treeview
 * Sugar CellRendererIcon has too much logic inside. It should only handle how to render itself.


 * Sugar CellRendererIcon is connected to many signals. Just detaching them while scrolling provides a performance boost.


 * Sugar CellRendererIcon could benefit from caching values instead of calculating them on each render.

but we could't confirm that.
 * There are a additional block in the Journal. That is not addressed by this feature, we guess there is a DBus blocking call,

Implementation
To use it, just do:
 * ScrollingDetector: A new class ScrollingDetector allow simplify slow operations while the treeview is scrolling.

scrolling_detector = ScrollingDetector(self._scrolled_window) scrolling_detector.connect_treeview(self._tree_view)


 * CellRendererIcon changes:

The CellRendererIcon is not a widget, then, do not receive events when the mouse enter or leaves, and all the logic in the CellRendererInvoker is more complex than should be. Worst, we had 6 different CellRendererIcons in the Journal, then we simplified (and solved issues) implementing a TreeViewInvoker. The TreeView knows where is every cell then the code is much more simple.

The ObjectPalettes was created in the mouse enter callback, then if a user moved the mouse cursor over the activity icons, many palettes were created, and that palette creation is expensive. Moving the palette creation to the treeview, we can create the palette when the mouse was in a cell for a specified timeout and not before.

GTK+ concepts

 * GtkTreeView — A widget for displaying both trees and lists https://developer.gnome.org/gtk3/stable/GtkTreeView


 * GtkTreeViewColumn — A visible column in a GtkTreeView widget https://developer.gnome.org/gtk3/stable/GtkTreeViewColumn.html


 * GtkCellRenderer — An object for rendering a single cell https://developer.gnome.org/gtk3/stable/GtkCellRenderer

Benefit to Sugar
Performance!

Scope
Affects Shell and Toolkit.

UI Design
We should not regress treeviews. Pay special attention to Journal list and activities list.

How To Test
To test the changes in the journal we used a python program to start the journal window from a terminal. You can download it here

To use it do:

python -m cProfile start_journal.py > profile.txt

After run it in a Sugar terminal, the view jump to the Home, but in the frame you can see two journal icons. The second is the profiled version. In the toolbar have a Stop button. After stop, you can check the profile.txt file.

User Experience
Users should notice a performance boost.

Dependencies
No deps.

Contingency Plan
These optimizations can come in small steps, so there is no need for a contingency plan.

Documentation
To be written.

Release Notes
To be written.

Comments and Discussion
Your comments are very welcome. Please discuss through the mailing list.

The initial announcement in the mailing list is here