Re: drawing on offscreen surface

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The code in expose_event_offscr actually draws on screen. Actually your
widget might use double buffering.
surface is the offscreen scene.
Or may be I just not understand your point.

Le vendredi 10 août 2012 à 14:58 +0530, Prasanta Sadhukhan a écrit :
> I have added the drawing of green rectangle in configure_event_cb()
> code where I am creating the surface.
> Now, when I run this I get BOTH the green rectangle and blue rectangle
> on the main window.
> I assume since I am not calling   cairo_set_source_surface() in
> configure_event_cb() that means the green rectangle is being drawn on
> main window and NOT on offscreen surface, whereas
> in expose_event(), since I am calling cairo_set_source_surface() and
> drawing blue rectangle on that surface, it is getting drawn on
> offscreen.
> Please confirm and second my understanding.
> 
> Thank you all for your help.
> 
> #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, 0, 0, 0);
>     cairo_paint(cr);
> 
>   cairo_set_source_rgb(cr, 0, 1, 0);
>   cairo_rectangle(cr, 100, 100, 200, 200);
>   cairo_stroke(cr);
> 
>     return FALSE;
> }
> 
> static gboolean
> expose_event_offscr (GtkWidget *widget,GdkEventExpose *event, gpointer
> data)
> {
>   g_print("draw event offscr\n");
> 
>   cairo_t *cr = gdk_cairo_create(widget->window);
>   cairo_set_source_surface(cr, surface, 0, 0);
>   cairo_paint(cr);
> 
>   cairo_set_source_rgb(cr, 0, 0, 1);
>   cairo_rectangle(cr, 300, 300, 200, 200);
>   cairo_stroke(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 (expose_event_offscr), 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;
> }
> 
> 
> On Fri, Aug 10, 2012 at 2:38 PM, Jean Brefort
> <jean.brefort@xxxxxxxxxxxxxx> wrote:
>         I suppose that surface is the offscreen scene. In that case,
>         ther bule
>         rectangle should not be drawn during the expose event
>         callback, but when
>         you build surface. Then you can use the code in my previous
>         message,
>         replacing the blue color by green color.
>         
>         Hope this helps.
>         
>         Le vendredi 10 août 2012 à 14:34 +0530, Prasanta Sadhukhan a
>         écrit :
>         > Thanks for your code. This draws a blue rectangle on a black
>         > background and the offscreen surface contents is rendered on
>         main
>         > window.
>         > But I also would like to draw green rectangle in main window
>         so after
>         > final rendering of offscreen contents (the blue rectangle)
>         on main
>         > window, I would get both blue and green rectangles on main
>         window.
>         > Can you please clarify how can I achieve that (both
>         offscreen & main
>         > window contents being shown on main window)?
>         >
>         > Thanks in advance!!
>         >
>         > Regards
>         > Prasanta
>         >
>         > On Fri, Aug 10, 2012 at 2:22 PM, Jean Brefort
>         > <jean.brefort@xxxxxxxxxxxxxx> wrote:
>         >         You should use something like:
>         >
>         >         cairo_set_source_surface(cr, surface, 0, 0);
>         >         cairo_paint(cr).
>         >         cairo_set_source_rgb(cr, 0, 0, 1);
>         >         cairo_rectangle(cr, 300,300, 200, 200);
>         >         cairo_stroke(cr);
>         >
>         >
>         >         This will paint the window with surface as source
>         and then
>         >         draw a blue
>         >         rectangle.
>         >
>         >         Le vendredi 10 août 2012 à 14:09 +0530, Prasanta
>         Sadhukhan a
>         >         écrit :
>         >         >
>         >         >
>         >         > On Fri, Aug 10, 2012 at 1:22 PM, Jean Brefort
>         >         > <jean.brefort@xxxxxxxxxxxxxx> wrote:
>         >         >         This code is quite strange. Your call to
>         >         >         cairo_set_source_surface() is
>         >         >         not useful since you use
>         cairo_set_source_rgb() just
>         >         after.
>         >         >         You should
>         >         >         call cairo_paint() just after
>         >         cairo_set_source_surface() if
>         >         >         you want it
>         >         >         to have any effect.
>         >         >
>         >         > If I do not call     cairo_set_source_rgb(cr, 0,
>         0, 1); how
>         >         will get a
>         >         > blue rectangle?
>         >         > Just having   these is giving me a window with
>         black
>         >         background.
>         >         > cairo_set_source_surface(cr, surface, 0, 0);
>         >         > cairo_rectangle(cr, 300,300, 200, 200);
>         >         > cairo_stroke(cr);
>         >         > cairo_paint(cr).
>         >         >
>         >         > Can you please clarify?
>         >         > As I told, I would like to get a blue rectangle in
>         offscreen
>         >         surface
>         >         > and a green rectangle in main visible surface so
>         after final
>         >         rendering
>         >         > of offscreen contents on main window, I would get
>         both
>         >         rectangles on
>         >         > main window.
>         >         >
>         >         > Regards
>         >         > Prasanta
>         >         >
>         >         >         Hope it helps,
>         >         >         Jean
>         >         >
>         >         >         Le vendredi 10 août 2012 à 13:07 +0530,
>         Prasanta
>         >         Sadhukhan a
>         >         >         écrit :
>         >         >         > expose_event (GtkWidget
>         *widget,GdkEventExpose
>         >         *event,
>         >         >         gpointer
>         >         >         > data)
>         >         >         > {
>         >         >         >   g_print("draw event main\n");
>         >         >         >
>         >         >         >   cairo_t *cr =
>         gdk_cairo_create(widget->window);
>         >         >         > // draw blue rectangle into offscreen
>         >         >         >   cairo_set_source_surface(cr, surface,
>         0, 0);
>         >         >         >   cairo_set_source_rgb(cr, 0, 0, 1);
>         >         >         >   cairo_rectangle(cr, 300, 300, 200,
>         200);
>         >         >         >   cairo_stroke(cr);
>         >         >         >   cairo_paint(cr);
>         >         >         >
>         >         >         > //draw green rectangle onto main window
>         >         >         >     cairo_set_source_rgb(cr, 0, 1, 0);
>         >         >         >   cairo_rectangle(cr, 100, 100, 200,
>         200);
>         >         >         >    cairo_stroke(cr)
>         >         >         > }
>         >         >         >
>         >         >         >
>         >         >         >
>         >         >
>         >         >
>         >         >
>         _______________________________________________
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>         >         >         gtk-list@xxxxxxxxx
>         >         >
>         https://mail.gnome.org/mailman/listinfo/gtk-list
>         >         >
>         >
>         >
>         >
>         >
>         
>         
>         
> 


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