gvalues

[suk <suk artax karlin mff cuni cz>]

I'm writing about minor performance disadvantage when accesing
style_property values. So it goes:

This code pattern is at several places. Example from GtkButon.c

 static const GtkBorder default_default_outside_border = { 0, 0, 0, 0 };
 static const GtkBorder default_default_border = { 1, 1, 1, 1 };

 .....

static void gtk_button_get_props (GtkButton *button,
                      GtkBorder *default_border,
                      GtkBorder *default_outside_border,
                      gboolean  *interior_focus)
{
  GtkWidget *widget =  GTK_WIDGET (button);
  GtkBorder *tmp_border;                       
  if (default_border)
    {
      gtk_widget_style_get (widget, "default_border", &tmp_border,NULL);

      if (tmp_border)
        {
          *default_border = *tmp_border;
          g_free (tmp_border);
        }
      else
        *default_border = default_default_border;
    }
....

This function is called from other code like this:

  GtkBorder default_border;
  gtk_button_get_props (button, &default_border, NULL, NULL);


This tries to get_style_property and if not found then return some
fallback value. But it unreasonably allocates/frees memory and copies
the value twice (branch when property exists) and once otherwise.
This of course goes against the idea in gtk_style_... to have access
to values fast.

Variant 1:

So maybe it would be better to have
  boolean  gtk_widget_style_get_property (widget, "default_border", &variable );
instead of
  void gtk_widget_style_get_property (widget, "default_border", &variable );


With this we can make it with only one copying (in each branch one).
      if (!gtk_widget_style_get (widget, "default_border", default_border, NULL))
            *default_border = default_default_border;
So one copying is done inside gtk_widget_style_get 
        - but this time, without alocating new struct.
and if there is no such property, we do copying outside.

I don't understand G_VALUES properly, but this would be fairly easy for
someone who does. 

Variant 2:
Of course we can make no copying at all. Because 

        void* gtk_widget_style_get_property (widget, "default_border" );

gets the value from style->property_cache, so if we promise to not touch
and not store for a long time.... This variant will not get through, i'm
sure.


Suk


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