Re: Draw on top of a window

[Lucas Hermann Negri <kkndrox gmail com>]

On Thu, Mar 11, 2010 at 11:41 PM, Richard Kung <richardkung linpus com> wrote:
> Hi,
>
> I want to use cairo to draw on top of a window but don't know how to achieve
> it.
> Below is my code.
> bottom_image is always on top of top_image.
> Any suggestion for beginners is welcome.
>
> Richard
>
> #include <cairo.h>
> #include <gtk/gtk.h>
>
> cairo_surface_t *top_image;
> GtkWidget *bottom_image;
>
> static gboolean on_expose_event(GtkWidget *widget, GdkEventExpose *event,
> gpointer data)
> {
>   cairo_t *cr;
>   cr = gdk_cairo_create(widget->window);
>   cairo_set_source_surface(cr, top_image, 0, 0);
>   cairo_paint(cr);
>   cairo_destroy(cr);
>
>   return FALSE;
> }
>
> int main(int argc, char *argv[])
> {
>   GtkWidget *window;
>
>   gtk_init(&argc, &argv);
>   window = gtk_window_new(GTK_WINDOW_TOPLEVEL);
>   top_image = cairo_image_surface_create_from_png("top.png");
>   bottom_image  = gtk_image_new_from_file("bottom.png");
>   gtk_container_add(GTK_CONTAINER(window), bottom_image);
>
>   g_signal_connect(window, "expose-event", G_CALLBACK (on_expose_event),
> NULL);
>   g_signal_connect(window, "destroy", G_CALLBACK (gtk_main_quit), NULL);
>   gtk_widget_set_app_paintable(window, TRUE);
>   gtk_window_set_position(GTK_WINDOW(window), GTK_WIN_POS_CENTER);
>   gtk_window_set_default_size(GTK_WINDOW(window), 200, 200);
>   gtk_widget_show_all(window);
>   gtk_main();
>
>   cairo_surface_destroy(top_image);
>   return 0;
> }
>
>
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>

Your callback should return TRUE, to indicate that the event shouldn't
be propagated further.

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