Hello all!
I'm working on a NodeKit (that is coming along nicely, btw) for using
the NVidia NV_path_rendering extension with OSG. This new extension has
an interesting--and, AFAIK, hitherto unseen--rendering model.
When using NV_path_rendering (which I will call NVPR), one must feed
path coordinate data into the OpenGL driver and it will "compile" this
data for you into resources the graphics context identifies by number.
This work fairly well in OSG using the Drawable override of
compileGLObjects(), since I am given a valid and active graphics context
which I can use to build the renderable objects.
(As a side node, for the uninitiated, a "path" in this context is a
N-order series of 2D coordinates that you use to draw vectors graphics;
for example, fonts. NVPR is an extension that uses your Cuda cores to
drastically speed this process up and create incredibly fast and
high-quality 2D graphics.)
I mentioned earlier that compiling these objects and making them
available to OSG (even as displayLists) is straightforward. HOWEVER,
there is an issue with regards to properly informing OSG of the bounding
boxes of these objects, a kind of "chicken-and-egg" problem. :)
Up until now, Drawable objects in OSG have had some kind of 3D geometric
data associated with them. This lets the object calculate the bounding
box on the CPU as the object is created, and inform the scenegraph
almost immediately what to expect with regards to its bounds. In NVPR,
we need the GPU to compute these bounds, but it cannot do so until AFTER
it has compiled the objects internally. This means it needs a valid
graphics context an should ideally do so towards the end of the
compileGLObjects method. As before, this is straightforward to execute,
but the order of operations here makes things tricky with OSG.
Consider the following:
osg::Geode* g = new osg::Geode();
osgNVPR::Path* p = new osg::PathCommands();
p->doStuff();
g->addDrawable(p);
// DOH! OSG wants to do bounding calculations here, but we
// haven't yet compiled or calculated the path internally
// until compileGLObjects is called!
I've come up with some workarounds, such as calling:
viewer.realize();
viewer.frame();
...and then manually calling dirtyBound(), but these feels very wrong to
me.
I wanted to quickly as the OSG community if they had any advice on how I
should best approach this problem. Drawble::dirtyBound() isn't a const
method, and so can't be easily called from compileGLObjects.
Perhaps there may be some way to "pre-compile" these paths with a valid
rendering context shortly after creating the Viewer?
At any rate, hope everyone has a great week! LABOR DAY EXTENDED WEEKEND!
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