Update the README with some background information - Federico

parent 02c7cf7b
......@@ -6,7 +6,67 @@ performant does not only mean "paint widgets fast". It also means
things like the time needed to set up widgets, to map and draw a
window for the first time, and emitting/propagating signals.
The following is accurate as of 2005/07/28.
The following is accurate as of 2006/Jun/14.
Background
----------
A widget's lifetime looks more or less like this:
1. Instantiation
2. Size request
3. Size allocate
5. Realize
4. Map
5. Expose
6. Destroy
Some of these stages are particularly interesting:
- Instantiation means creating the widget. This may be as simple as a
few malloc()s and setting some fields. It could also be a
complicated operation if the widget needs to contact an external
server to create itself, or if it needs to read data files.
- Size requisition is when GTK+ asks the widget, "how big do you want
to be on the screen"? This can be an expensive operation. The
widget has to measure its text, measure its icons (and thus load its
icons), and generally run through its internal layout code.
- Realization is when the widget creates its GDK resources, like its
GdkWindow and graphics contexts it may need. This could be
expensive if the widget needs to load data files for cursors or
backgrounds.
- Expose is when the widget gets repainted. This will happen many
times throughout the lifetime of the widget: every time you drag a
window on top of it, every time its data changes and it needs to
redraw, every time it gets resized.
GtkWidgetProfiler is a mechanism to let you get individual timings for
each of the stages in the lifetime of a widget. It also lets you run
some stages many times in a sequence, so that you can run a real
profiler and get an adequate number of samples. For example,
GtkWidgetProfiler lets you say "repaint this widget 1000 times".
Why is this not as simple as doing
start_timer ();
for (i = 0; i < 1000; i++) {
gtk_widget_queue_draw (widget);
while (gtk_events_pending ())
gtk_main_iteration ();
}
stop_timer ();
Huh?
Because X is an asynchronous window system. So, when you send the
"paint" commands, your program will regain control but it will take
some time for the X server to actually process those commands.
GtkWidgetProfiler has special code to wait for the X server and give
you accurate timings.
Using the framework
......@@ -132,6 +192,8 @@ main (int argc, char **argv)
gtk_widget_profiler_set_num_iterations (profiler, 100);
gtk_widget_profiler_profile_boot (profiler);
gtk_widget_profiler_profile_expose (profiler);
return 0;
}
......
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