gtk2/perf/README

README for gtk+/perf
--------------------

This is a framework for testing performance in GTK+.   For GTK+, being
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.


Using the framework
-------------------

Right now the framework is very simple; it just has utility functions
to time widget creation, mapping, exposure, and destruction.  To run
such a test, you use the GtkWidgetProfiler object in
gtkwidgetprofiler.h.

The gtk_widget_profiler_profile_boot() function will emit the
"create-widget" signal so that you can create your widget for
testing.  It will then take timings for the widget, and emit the
"report" signal as appropriate.

The "create-widget" signal:

  The handler has this form:

    GtkWidget *create_widget_callback (GtkWidgetProfiler *profiler, 
				       gpointer user_data);

  You need to create a widget in your handler, and return it.  Do not
  show the widget; the profiler will do that by itself at the right
  time, and will actually complain if you show the widget.


The "report" signal:

  This function will get called when the profiler wants to report that
  it finished timing an important stage in the lifecycle of your
  widget.  The handler has this form:

    void report_callback (GtkWidgetProfiler      *profiler,
			  GtkWidgetProfilerReport report,
			  GtkWidget              *widget,
			  gdouble                 elapsed,
			  gpointer                user_data);

  The "report" argument tells you what happened to your widget:

    GTK_WIDGET_PROFILER_REPORT_CREATE.  A timer gets started right
    before the profiler emits the "create-widget" signal,, and it gets
    stopped when your callback returns with the new widget.  This
    measures the time it takes to set up your widget, but not show it.

    GTK_WIDGET_PROFILER_REPORT_MAP.  A timer gets started right before
    the profiler calls gtk_widget_show_all() on your widget, and it
    gets stopped when the the widget has been mapped.

    GTK_WIDGET_PROFILER_REPORT_EXPOSE.  A timer gets started right before
    the profiler starts waiting for GTK+ and the X server to finish
    painting your widget, and it gets stopped when the widget is fully
    painted to the screen.

    GTK_WIDGET_PROFILER_REPORT_DESTROY.  A timer gets started right
    before the profiler calls gtk_widget_destroy() on your widget, and
    it gets stopped when gtk_widget_destroy() returns.

As a very basic example of using GtkWidgetProfiler is this:

----------------------------------------------------------------------
#include <stdio.h>
#include <gtk/gtk.h>
#include "gtkwidgetprofiler.h"

static GtkWidget *
create_widget_cb (GtkWidgetProfiler *profiler, gpointer data)
{
  GtkWidget *window;

  window = gtk_window_new (GTK_WINDOW_TOPLEVEL);
  /* ... fill the window with widgets, and don't show them ... */

  return window;
}

static void
report_cb (GtkWidgetProfiler *profiler, GtkWidgetProfilerReport report, GtkWidget *widget, gdouble elapsed, gpointer data)
{
  const char *type;

  switch (report) {
  case GTK_WIDGET_PROFILER_REPORT_CREATE:
    type = "widget creation";
    break;

  case GTK_WIDGET_PROFILER_REPORT_MAP:
    type = "widget map";
    break;

  case GTK_WIDGET_PROFILER_REPORT_EXPOSE:
    type = "widget expose";
    break;

  case GTK_WIDGET_PROFILER_REPORT_DESTROY:
    type = "widget destruction";
    break;

  default:
    g_assert_not_reached ();
    type = NULL;
  }

  fprintf (stderr, "%s: %g sec\n", type, elapsed);

  if (report == GTK_WIDGET_PROFILER_REPORT_DESTROY)
    fputs ("\n", stderr);
}

int
main (int argc, char **argv)
{
  GtkWidgetProfiler *profiler;

  gtk_init (&argc, &argv);

  profiler = gtk_widget_profiler_new ();
  g_signal_connect (profiler, "create-widget",
		    G_CALLBACK (create_widget_cb), NULL);
  g_signal_connect (profiler, "report",
		    G_CALLBACK (report_cb), NULL);

  gtk_widget_profiler_set_num_iterations (profiler, 100);
  gtk_widget_profiler_profile_boot (profiler);
  
  return 0;
}

----------------------------------------------------------------------


Getting meaningful results
--------------------------

Getting times for widget creation/mapping/exposing/destruction is
interesting, but how do you actually find the places that need
optimizing?

Why, you run the tests under a profiler, of course.

FIXME: document how to do this.


Feedback
--------

Please mail your feedback to Federico Mena-Quintero <federico@novell.com>.
This performance framework is a work in progress.