> 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 <
tadeboro 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
>
tadeboro gmail com
>
tadej borovsak gmail com
>
>
