[osg-users] switch between two camera

Peter Amstutz peter.amstutz at tseboston.com
Tue Mar 17 05:57:01 PDT 2009


Robert Osfield wrote:
> Hi Peter, Benoit et,
>
> On Mon, Mar 16, 2009 at 8:15 PM, Peter Amstutz 
> <peter.amstutz at tseboston.com <mailto:peter.amstutz at tseboston.com>> wrote:
>
>     The way I handled this in my application was to create multiple
>     instances of osgViewer::Viewer with a separate camera for each
>     view but all bound to the same output window.  On each render
>     iteration, draw just the active camera.
>
>
> I'm afraid I really wouldn't recommend this solution, having multiple 
> viewers just to alternate between views is complicated implementation 
> and conceptual wise and you'd be very lucky for it to work in anything 
> other that very limited usage models.  Using multiple viewers will 
> cause problems with threading, timing codes, it'd be a right old mess.
Well, I force it to use single threading since my render thread already 
runs independently of the main logic thread.  This avoids most of the 
problems you mention, but in general I wouldn't recommend this solution 
either.  I just thought I'd throw it out there because it has worked for 
me so far.  I think I am doing it this way because I originally wrote my 
code for OSG 1.2, which didn't have any of the nice osgViewer 
infrastructure.
>  
>
>     The best solution depends on exactly what you need to display; I
>     decided to switch between completely independent scenes because my
>     2D and 3D views looks actually render somewhat different geometry
>     (the 2D ortho view is an abstracted version of the "real" 3D
>     geometry).  Having entirely separate scenes is also pretty
>     straightforward although it imposes some overhead due to
>     duplication of resources that could otherwise be shared between
>     among views.
>
>
> In your case you are talking about multiple Views, and this is fine, 
> but you don't use multiple Viewers for it, you'd use a single 
> CompositeViewer with multiple Views.  You can add and remove Views, or 
> just toggle Camera's on/off using NodeMask's.
I'll take a look at this.  The (doxygen) documentation is a bit thin 
here, so I wasn't sure what exactly CompositeViewer was for -- I assumed 
it was for rendering multiple subwindows of a single main window.

I'm still fuzzy on the relationship between Graphics Context, View, 
Viewer, Camera, Scene -- there's at least a couple layers of abstraction 
there.  Especially when I see inheritance graphs like this 
(http://www.openscenegraph.org/documentation/OpenSceneGraphReferenceDocs/a01055.html)   
:-)

- Peter




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