[Gtk-sharp-list] Best way to continuously update a Gtk.Image (V4L)

Sebastian scut@nb.in-berlin.de
Sat, 17 Apr 2004 12:47:37 +0800

Hi everybody,

I am really happy that Debian/sid now has up to date gtk# packages (thanks
to Mr. Bloch) and it is really fun to code with gtk#. Thanks gtk# guys! :)

I am planning to use Gtk# as GUI framework for a video4linux related
application. I use a small C glue to the v4l interface and a Gdk.Pixbuf
within Gtk.Image to display a continously updated image.

Currently, it looks like this, within Main() of my test application:


        vl.StartCapture ();
        while (true) {
            vl.GetFrame ();
            conv.ConvertCurrentFrame ();
            img.QueueDraw ();

            // Free frame buffer and process GTK events, because we have some
            // free time now until the next frame is catched.
            vl.FreeFrame ();
            while (Application.EventsPending ())
                Application.RunIteration ();


The conv.ConvertCurrentFrame function just overwrites/updates the Pixels
array within the Gdk.Pixbuf that is displayed by the GUI and then calls a
QueueDraw on the wrapped Gtk.Image.

The while loop is from the Gtk# documentation, albeit I think its not the
normal usage here.

Now, here come the questions:

 1. Is just overwriting the Pixbuf byte array and queuing a redraw the
    proper way or may this pointer change somehow?

 2. How to call this from the Gtk# main loop? There is no main loop at the
    moment, and if I try to close the window, I get this message:

	(<unknown>:1970): Gtk-CRITICAL **: file gtkmain.c: line 1151
		(gtk_main_quit): assertion `main_loops != NULL' failed

    I do not want the user to have to click a start-button or the like.

 3. As the GetFrame() function in my glue calls an ioctl that blocks, I will
	have to run it in another thread. Is it still ok for Gtk# to just let
	this thread continuously overwrite the Pixels array? How to call the
	QueueDraw method so it is queued within the Gtk# mainloop thread and not
    the ioctl-thread?

Thanks for bearing with my newbie questions in advance,

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