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: 0.102
• Last updated: Feb 24, 2014
• Percentage of completion: 60%

Detailed Description

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

• Sugar CellRendererIcon has too much logic inside. It should only handle how to render itself.

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 [1]

• 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.

• There are a additional block in the Journal. That is not addressed by this feature, we guess there is a DBus blocking call,

but we could't confirm that.

Implementation

• ScrollingDetector: A new class ScrollingDetector allow simplify slow operations while the treeview is scrolling.

To use it, just do:

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 [2]. 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

We did a test program that has a list (treeview) with many rows. Each row has a cellrenderer icon. The program automatically starts scrolling until the end of the list is reached. Then we can get profiling information using Python cProfile http://docs.python.org/2/library/profile.html . We ran the test like this inside a Sugar shell:

   python -m cProfile test_treeview.py > profile.txt

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.