[osg-users] Offscreen rendering (e.g. pbuffer) and event processing

[Émeric MASCHINO]

Hi,

I should have said that I was drawing the viewer in a pixel buffer in
my other question [1], that now leads to this one...
I'm streaming the pixel buffer data and displaying/manipulating the
scene in/from a webpage.
The offscreen viewer obviously hasn't any window, nor associated event queue.
I would like to forward the keyboard/mouse inputs emitted by the
JavaScript code in my webpage, so that I can leverage upon the OSG
manipulators (namely, trackball).

At the moment, I'm doing the following:

viewer.getEventQueue()->setGraphicsContext(pbuffer);
viewer.getEventQueue()->syncWindowRectangleWithGraphcisContext();

These operations are normally performed when initializing a
GraphicsWindow, e.g. in GraphicsWindowWin32::init() and are thus
missing when initializing a pbuffer, in e.g. PixelBufferWin32::init().

The syncWindowRectangleWithGraphcisContext (ever noticed the
misspelling?) was the missing thing for me in [1]. Thus, the
GUIEventAdapter created when processing an event in the EventQueue had
its _Xmin, _Xmax, _Ymin, _Ymax, _windowWidth and _windowHeight had
their default values.

So, am I adding correctly an event queue to an offscreen viewer/view this way?

Émeric

[1] http://lists.openscenegraph.org/htdig.cgi/osg-users-openscenegraph.org/2015-February/269273.html
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[Robert Osfield]

Hi Émeric,

Thanks for spotting to typo.  I hadn't noticed this before, and it hadn't been reported either.  I am fixing this and will get it checked in once my clean build has completed.

As for implementing an off screen viewer functionality using a pbuffer.  I haven't ever tried this on contemplated it.  It should be possible to mimic traditional window events by injecting them into the EventQueue, and you've spotted passing on the appropriate window size will be required.   I can't provide any specific advice though as you are already further down the road of trying something I haven't done yet :-)

Robert.

[Émeric MASCHINO]

Hi Robert,

> Thanks for spotting to typo. I hadn't noticed this before, and it hadn't
> been reported either. I am fixing this and will get it checked in once my
> clean build has completed.

My first major contribution to the OSG community ;-)

> As for implementing an off screen viewer functionality using a pbuffer. I
> haven't ever tried this on contemplated it. It should be possible to mimic
> traditional window events by injecting them into the EventQueue, and you've
> spotted passing on the appropriate window size will be required. I can't
> provide any specific advice though as you are already further down the road
> of trying something I haven't done yet :-)

OK, thanks for feedback.

For completeness, you'll also had to override
ViewerBase::checkEvents() if you want to leverage on viewer's
on-demand run scheme. Indeed, the Viewer and CompositeViewer
implementations only check for events from devices and windows. With
an off-screen viewer, you won't get any window, only views for which
you need to take care of setting a graphics contexts as I proposed
previously.

For a CompositeViewer-inherited off-screen viewer, checkEvents() looks like:

bool OffscreenViewer::checkEvents()
{
if (CompositeViewer::checkEvents())
return true;

Views views;
getViews(views);

// Check events from any views
for (Views::iterator vitr = views.begin();
vitr != views.end();
++vitr)
{
if ((*vitr)->getEventQueue() && !((*vitr)->getEventQueue()->empty()))
return true;
}

return false;
}

Hope this helps,

Émeric