One solution is naturally to create a new class that would inherit the osg::ComputeBoundVisitor, and use that. I don't like that idea as the ComputeBoundVisitor does actually have what I need - it is only hidden in a protected function.
I am therefor suggesting a slight generalization of the ComputeBoundVisitor with the attached patch, which is tested.
The patch has two parts:
we add applyBBox() so that one can use that in a customized traverse-function and add a bbox to the visitor. I considered calling this function expandByBBox(), but I though applyBBox was better.
The MatrixStack is made available to the outside world. That enables a traverse-function to do whatever it wishes.
I do actually only need one of the two, as I can implement what I wish either way, but adding getMatrixStack() will make more generic expansions possible.
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From Robert Osfield, changed the name of the new applyBBox(..) method to applyBoundingBox(..) to keep it's naming more consistent with the rest of the OSG.
