[Qt-interest] Intercepting Phonon VideoWidget frames

[Trenton Tuggle]

Ha!  Good catch!

I've tried two approaches with that:

I tried making the VideoWidget a child widget of the WidgetImager --  
children should always be painted on their parents, right?  (Not  
necessarily true for VideoWidget)
I tried changing WidgetImager to derive from VideoWidget -- derived  
classes *are* the parents, and should therefore receive all their  
parents' events, right?  (Maybe, but VideoWidet has backend-specific  
private detail implementation classes which are free to do whatever...  
including bypassing PaintEvents!)

Neither case receives the events because I don't believe VideoWidget  
uses them in a "normal" fashion.  For performance, I believe  
VideoWidgets do whatever they need, bypassing the normal painting  
system.

In fact, VideoWidgets seem to only be able to render() their contents  
anywhere if they're stuck inside a QGraphicsScene, so, as I mentioned,  
I created a "dummy" graphics scene and stuck one in it, and presto! I  
was able to render() frames to a QImage.

Unfortunately, there appears now to be some problem with rendering it  
too quickly... it doesn't draw anything unless I wait a second or two  
between calling render()!

There are several problem with this approach.  First, I'd imagine this  
behavior is common to all backend-implementations, but I'm not  
positive.  Second, the problem with rendering frames too often.   
Third, not sure of the overhead of the dummy graphicsscene.  Finally,  
even if it worked, you have to "poll" the video or figure out if it's  
changed; there's no notification of the update.

If phonon ever gets used for more than playback, it'll probably  
acquire features that'll help with what I need... but it's not there  
yet, and I'm not sure I'll be able to make it work within my time  
constraints on this project.  Perhaps next time...

-Trent Tuggle <Trent at Tuggle.Org>

On Mar 27, 2009, at 4:03 AM, Richard Moe Gustavsen wrote:

>> I've tried creating a QWidget-derived container (the source code I
>> posted earlier) but it still didn't receive PaintEvents.
>
> I took a quick look at the code, but I'm a bit uncertain about it.  
> As far as
> I can read, that code should only receive paint events for the  
> WidgetImager,
> and not from any video widget?
>
> Have you tried installing an event filter on the video widget (or more
> important, it's children, since thats where the drawing happends)  
> and look
> for paint events?
>
> -Richard
>
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