ok. I understand. Thanks all for your help.
On Fri, Aug 10, 2012 at 4:49 PM, Jean Brefort
<jean.bref...@normalesup.org>wrote:
> It is not the sme thing. With your latest code, you create surface each
> time the widget needs redraw. configure events only occur when the
> widget changes size.
> Otherwise, you are leaking surface and off_cr.
>
> Le vendredi 10 août 2012 à 16:41 +0530, Prasanta Sadhukhan a écrit :
> > Thanks for the code and the explanation. Now, it's quite clear.
> > Last thing I wanted to know is, do I need to always have
> > "configure_event" handler to create the offscreen surface.
> > Can't we create the offscreen surface in "expose_event" handler
> > itself?
> > I tried with this (after commenting "configure_event" callback) which
> > also seems to do the same thing as your code.
> >
> > static gboolean
> > draw_cb (GtkWidget *widget,
> > GdkEventExpose *event,
> > gpointer data)
> > {
> > cairo_t *off_cr, *cr;
> >
> > g_print("draw event\n");
> >
> > surface = gdk_window_create_similar_surface (event->window,
> > CAIRO_CONTENT_COLOR,
> > event->area.width,
> > event->area.height);
> >
> > off_cr = cairo_create(surface);
> > cairo_set_source_rgb(off_cr, 1, 0, 0);
> > cairo_paint (off_cr);
> >
> > cairo_move_to (off_cr, 100, 100);
> > cairo_set_source_rgb (off_cr, 0, 0, 0);
> > cairo_set_font_size (off_cr, 20);
> > cairo_show_text (off_cr, "Offscreen buffer is red");
> >
> >
> > cr = gdk_cairo_create (event->window);
> > cairo_set_source_surface(cr, surface, 0, 0);
> > cairo_paint(cr);
> >
> > cairo_move_to (cr, 200, 200);
> > cairo_set_source_rgb (cr, 0, 1, 0);
> > cairo_set_font_size (cr, 20);
> > cairo_show_text (cr, "This text is not blitted");
> >
> > cairo_destroy (cr);
> >
> > return TRUE;
> > }
> >
> > Regards
> > Prasanta
> > On Fri, Aug 10, 2012 at 4:14 PM, Tadej Borovšak <tadeb...@gmail.com>
> > wrote:
> > Hello.
> >
> > Have a look at this code (targeted at GTK+-2.x):
> >
> > #include <gtk/gtk.h>
> >
> > static cairo_surface_t *surface = NULL;
> >
> > static gboolean
> > configure_event_cb (GtkWidget *widget,
> > GdkEventConfigure *event,
> > gpointer data)
> > {
> > cairo_t *cr;
> >
> > g_print("configure event: %d, %d\n", event->width,
> > event->height);
> >
> > if (surface)
> > cairo_surface_destroy (surface);
> >
> > surface = gdk_window_create_similar_surface (event->window,
> >
> > CAIRO_CONTENT_COLOR,
> > event->width,
> > event->height);
> >
> > cr = cairo_create(surface);
> >
> > cairo_set_source_rgb(cr, 1, 0, 0);
> > cairo_paint (cr);
> >
> >
> > cairo_move_to (cr, 100, 100);
> > cairo_set_source_rgb (cr, 0, 0, 0);
> > cairo_set_font_size (cr, 20);
> > cairo_show_text (cr, "Offscreen buffer is red");
> >
> > cairo_destroy(cr);
> >
> > return FALSE;
> > }
> >
> > static gboolean
> > draw_cb (GtkWidget *widget,
> >
> > GdkEventExpose *event,
> > gpointer data)
> > {
> > cairo_t *cr;
> >
> > g_print("draw event\n");
> >
> > cr = gdk_cairo_create (event->window);
> >
> > cairo_set_source_surface(cr, surface, 0, 0);
> > cairo_paint(cr);
> >
> >
> > cairo_move_to (cr, 200, 200);
> > cairo_set_source_rgb (cr, 0, 1, 0);
> > cairo_set_font_size (cr, 20);
> > cairo_show_text (cr, "This text is not blitted");
> >
> > cairo_destroy (cr);
> >
> > return TRUE;
> > }
> >
> > int
> > main(int argc,
> > char **argv)
> > {
> > GtkWidget *window,
> > *area;
> >
> > gtk_init(&argc, &argv);
> >
> > window = gtk_window_new(GTK_WINDOW_TOPLEVEL);
> > gtk_window_set_default_size (GTK_WINDOW (window), 1200,
> > 800);
> > g_signal_connect (window, "destroy", gtk_main_quit, NULL);
> >
> > area = gtk_drawing_area_new();
> > g_signal_connect (area, "expose-event",
> >
> > G_CALLBACK (draw_cb), NULL);
> > g_signal_connect (area, "configure-event",
> > G_CALLBACK(configure_event_cb), NULL);
> > gtk_container_add (GTK_CONTAINER (window), area);
> >
> > gtk_widget_show_all(window);
> > gtk_main();
> >
> > return 0;
> > }
> >
> >
> >
> > surface is your offscreen buffer and contains red background
> > and black
> > text. This is then blitted during expose-event and to finish
> > off, some
> > green text is added. And that's it.
> >
> > Cheers,
> > Tadej
> >
> >
> > --
> > Tadej Borovšak
> > blog.borovsak.si
> > tadeb...@gmail.com
> > tadej.borov...@gmail.com
> >
> >
>
>
>
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