Paul, I had a similar problem (I think). I installed a custom callback on the RTT camera (CullSettings::setClampProjectionMatrixCallback). This callback would call the original implementation first, then store the results of the projection matrix clamp so that I could use it immediately.
You can see the custom callback here: https://github.com/gwaldron/osgearth/blob/master/src/osgEarth/ClampingTechnique.cpp#L171 Each frame, I prime it with the current CullVisitor: https://github.com/gwaldron/osgearth/blob/master/src/osgEarth/ClampingTechnique.cpp#L384 And then immediately use the result to set a uniform: https://github.com/gwaldron/osgearth/blob/master/src/osgEarth/ClampingTechnique.cpp#L403 Hope this helps. Glenn Waldron / @glennwaldron / osgEarth.org On Fri, Dec 14, 2012 at 3:12 PM, Paul Martz <[email protected]> wrote: > I think I have a pretty good idea of the cause. > > The CullVisitor gathers near & far info during traversal but doesn't > actually compute the final projection matrix until after the traversal > completes. This means, obviously, that the projection matrix for the > current frame hasn't been computed at the time the CullVisitor encounters > my post-render Camera. Instead, the CullVisitor inserts last frame's > projection matrix into the render graph, which is used for the box > rendering. Then it completes traversal, computes the *correct* projection > matrix, and uses this new matrix for the viewer root Camera's cylinder > rendering. Thus, the two projection matrices are off just slightly, and the > result is incorrect z interaction. > > But knowing this, I haven't been able to come up with a workaround. (Okay, > well, short of editing the render graph after cull, which seems like I'd be > asking for trouble.) So, still hoping for input from the community on how > to make this work without visual artifacts. Thanks. > -Paul > > > On 12/14/2012 11:28 AM, Paul Martz wrote: > >> Hi all -- I'm attempting to render with two Cameras, where one inherits >> the >> projection matrix of the other. But there appears to be some latency such >> that >> the subordinate Camera doesn't get the projection matrix until one frame >> late. >> You can reproduce the issue with the attached example and animation path. >> >> The example configures the viewer's root Camera to render to an FBO with >> color >> and depth textures attached. It renders a cylinder into these textures. A >> post-render Camera then splats the color texture into the window with a >> full >> screen quad. >> >> The problem occurs when a final post-render Camera draws the checkerboard >> box. >> It uses the depth texture an input to a fragment shader that performs a >> manual >> depth test. I have taken steps to ensure that this post-render Camera has >> RELATIVE_RF ref frame, and set it to disable near & far computation, so >> that it >> will inherit the projection matrix of the viewer root Camera. This works >> quite >> well except for the slight lag, indicating that this post-render Camera >> doesn't >> get the correct projection matrix until about a frame too late. >> >> The problem is definitely related to the fact that the viewer root Camera >> is >> configured to auto-compute near & far, because if I disable this and set >> a fixed >> projection matrix on the root Camera, the problem goes away (uncomment >> lines 49 >> and 50). >> >> Can anyone explain the one-frame lag with the projection matrix? I'll be >> digging >> into the code over the weekend to figure this out myself, but would >> appreciate >> any input while I dig... >> >> Thanks, >> -Paul >> >> >> >> >> >> ______________________________**_________________ >> osg-users mailing list >> osg-users@lists.**openscenegraph.org <[email protected]> >> http://lists.openscenegraph.**org/listinfo.cgi/osg-users-** >> openscenegraph.org<http://lists.openscenegraph.org/listinfo.cgi/osg-users-openscenegraph.org> >> >> ______________________________**_________________ > osg-users mailing list > osg-users@lists.**openscenegraph.org <[email protected]> > http://lists.openscenegraph.**org/listinfo.cgi/osg-users-** > openscenegraph.org<http://lists.openscenegraph.org/listinfo.cgi/osg-users-openscenegraph.org> >
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