[cairo] Threaded animation with cairo_gl backend over a GtkWidget

Carlos López González genetita at gmail.com
Sat Jan 12 02:29:34 PST 2013

looks like it doesn't work. I've added XInitThreads() and it still
crashing. Also added XLockDisplay and XUnlockDisplay with the same result.
Any idea?

int main (int argc, char *argv[])



         return 0;



    gtk_init(&argc, &argv);

    GtkWidget *window = gtk_window_new(GTK_WINDOW_TOPLEVEL);

    g_signal_connect(window, "destroy", G_CALLBACK(gtk_main_quit), NULL);

    gtk_window_set_title(GTK_WINDOW(window), "cairo_gl");

    gtk_window_set_default_size(GTK_WINDOW(window), 400, 300);

    gtk_widget_set_app_paintable(window, TRUE);

    gtk_widget_set_double_buffered(window, FALSE);



     (void)g_timeout_add(33, (GSourceFunc)timer_exe, window);




    return 0;


void *do_draw(void *ptr)



     cairo_t *cr = cairo_create(window_surface);


return NULL;

   Display *dpy =cairo_glx_device_get_display((cairo_surface_get_device(


    //do some time-consuming drawing here ...

    // ...

    // ...


    cairo_gl_surface_swapbuffers (window_surface);



    return NULL;


2013/1/11 Carlos López González <genetita at gmail.com>

> Thanks Henry, I'll give it a try.
> 2013/1/11 Henry (Yu) Song - SISA <hsong at sisa.samsung.com>
> Hi,
>> Please add XInitThreads() in your main.  For multithreaded application
>> using gl_surface is not a good idea for the moment unless you have
>> intel/radeon/nouveau drivers, otherwise, you will have very sloooooow
>> performance.
>> We will resolve that soon in cairo for gl backend, I hope.
>> Henry
>> ________________________________________
>> From: cairo-bounces+henry.song=samsung.com at cairographics.org[cairo-bounces+henry.song=
>> samsung.com at cairographics.org] on behalf of Carlos López González [
>> genetita at gmail.com]
>> Sent: Thursday, January 10, 2013 11:26 AM
>> To: cairo at cairographics.org
>> Subject: [cairo] Threaded animation with cairo_gl backend over a GtkWidget
>> Hi!
>> I've made a modified version [1] of the example of threaded animation
>> using Cairo [2].
>> First I've used the method to create a cairo_gl_surface from the
>> test/gl_source_surface.c file adapted to create the surface for a given
>> widget instead for a defined size.
>> Also, for simplicity, I removed all the handled signals except the
>> destroy one.
>> To handle the drawing for the window widget using the cairo_gl backend I
>> use the create_gl_surface_for_window function passing it the proper widget
>> information.
>> So far, for a single drawing execution it works as expected:
>> 1) In main() create the window_surface
>> 2) The do_draw function creates a context based on window_surface
>> 3) Once done the drawings with Cairo then the buffers are swapped and the
>> content is shown on screen.
>> Notice that the window_surface is never destroyed explicitly because it
>> is owned by the window widget and so it will be destroyed when the window
>> is destroyed by gtk.
>> The problem comes when I enable the multithreading support by
>> uncommenting the line:
>> //(void)g_timeout_add(33, (GSourceFunc)timer_exe, window);
>> It triggers the timer_exe function 33 times per second and then it
>> creates threads that will call do_draw each time.
>> Once enabled it crashes at the first painting function from Cairo.
>> I believe that the problem is that the window_surface belongs to the
>> window widget when I created it and then I can't modify it outside the main
>> gtk thread.
>> How can I solve this? If I enclose the Cairo painting operations inside a
>> gdk_threads_enter and
>> gdk_threads_leave I would add a lot of time consuming operations to the
>> main gtk thread, which is precisely what I want to avoid using
>> multithreading.
>> Any help? I would like to know at last, if my assumptions of the
>> window_surface ownership are true or not.
>> Thanks!
>> [1]
>> https://github.com/genete/my-test-area/blob/direct_draw/src/cairo_sample.c
>> [2] http://cairographics.org/threaded_animation_with_cairo/
>> --
>> Carlos
>> http://synfig.org
> --
> Carlos
> http://synfig.org

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