Re: drawing moving shapes

[Michael L Torrie <torriem chem byu edu>]

On Fri, 2007-02-02 at 16:02 -0700, Rob Barnes wrote:
> I am using gtk_widget_queue_draw() already. The doc says,"Once the main loop
> becomes idle (after the current batch of events has been processed,
> roughly), the window will receive expose events for the union of all regions
> that have been invalidated.", but this does not seem to be happening.
> Placing a printf in my expose event revealed that expose is not being called
> unless I move the mouse or something like that.  My program is
> multithreaded, could that be causing problems?

I was going to ask if your program was multithreaded as this is classic
behavior when you try to use threads.  

Did you read the documentation on how to properly use threads in GTK?
Are you initializing thread support in gdk?  Do you properly lock gdk
when making any gtk or gdk call from a thread?

In general (on all platforms and all widget toolkits), making gui calls
from the thread is a bad idea.  Instead, notify the main loop when you
want it to do something by doing g_idle_add and a callback.  This
ensures that the callback, which could update the drawing area, for
example, runs in the main thread at the next opportunity.  Note that you
have to synchronize any data that you want to share between threads
using locking primitives.

Michael


> Some code snippets:
>
> GtkWidget *drawing_area;
> ....
> //Inside main:
> drawing_area = gtk_drawing_area_new ();
> g_signal_connect (G_OBJECT (drawing_area), "expose_event", G_CALLBACK
> (expose_event), NULL);
> gtk_widget_set_events(drawing_area,GDK_ALL_EVENTS_MASK);
> ....
>
> gboolean expose_event( GtkWidget      *widget,
>                               GdkEventExpose *event )
> {
> printf("expose\n");
>     //draw_player(players[0]);
>   gdk_draw_drawable (widget->window,
>              widget->style->fg_gc[GTK_WIDGET_STATE (widget)],
>              pixmap,
>              event->area.x, event->area.y,
>              event->area.x, event->area.y,
>              event->area.width, event->area.height);
>
>   return FALSE;
> }
>
> //Inside a asynchronous function
> //marker is an ADT
> gdk_draw_polygon (pixmap,marker.kontext,TRUE,marker->poly,4);
> ....
> gdk_widget_queue_draw(drawing_area);
> ....
>
> Thanks.
> -RobB
>
>
> On 2/2/07, Michael Ekstrand <mekstran scl ameslab gov> wrote:
> > On Fri, 2007-02-02 at 12:20 -0700, Rob Barnes wrote:
> > > I'm trying to write a simple program that draws a moving polygon on the
> > > screen. I started with the scribble-simple example and modified to draw
> > the
> > > moving shape by redrawing the shape in the background color in the
> > previous
> > > position first then drawing it in the foreground color in the current
> > > position. It works fine, except it only refreshes when something happens
> >
> > > such as mouse movement, click, expose, window adjustment. So to keep
> > things
> > > moving I have to keep moving the mouse around, but it stops if the mouse
> > > stops, even though the polygon is being redrawn contently.
> >
> > Make sure you request a redraw every time the underlying state changes -
> > check out gtk_widget_queue_draw.
> >
> > --
> > Michael Ekstrand
> > Research Assistant, Scalable Computing Laboratory
> > Goanna, compute cluster and InfiniBand network monitor tool:
> >         http://www.scl.ameslab.gov/Projects/Monitor/
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