[osg-users] ComputeBoundsVisitor does not consider Billboards

[Guy Volckaert]

Hi,

I'm having problem with the osg::ComputeBoundsVisitor and osg::Billboards. In essence, the osg::ComputeBoundsVisitor does not consider the pivot position of the facing billboard. For example, let say I have a simple model that contains a single facing quad billboard (like a tree) located at (20, 20, 0) with a dimension of (10, 0, 10). I would expect the osg::ComputeBoundsVisitor to calculate a scene bounding box of min(15, 20, 0) max(25, 20, 10). However, what I seem to get instead is min(-5, 0, 0 ) max( 5, 0, 10 ).

My investigation led me to review osg::ComputeBoundsVisitor and I found that it does not consider billboards - i.e. the osg::ComputeBoundsVisitor::apply(osg::Billboard& billboard) is missing. In effect, the osg::ComputeBoundsVisitor does not consider the pivot position stored in osg::Billboard::_positionList.

Is this design intentional? If not, then how would you propose fixing this issue?

Thank you!

Cheers,
Guy

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[Robert Osfield]

Hi Guy,

On 20 October 2017 at 15:34, Guy Volckaert <guy.vo...@meggitt.com> wrote:

My investigation led me to review osg::ComputeBoundsVisitor and I found that it does not consider billboards - i.e. the osg::ComputeBoundsVisitor::apply(osg::Billboard& billboard) is missing. In effect, the osg::ComputeBoundsVisitor does not consider the pivot position stored in osg::Billboard::_positionList.

Is this design intentional? If not, then how would you propose fixing this issue?

This is a design/implementation bug, looking that the implementation it's clearly too simple and misses the special case of handling osg::Billboard. 

To fix the bug a ComputeBoundVisitor::apply(osg::Billboard&) is required, the implementation of this new method would need to iterator through the _positionList and the drawables associated with each position and account for the full rnage of potistions that are possible for each drawables bounding box given the possible rotation and translation required.  The easiest way to do this would be to use the diameter of each drawable child's bounding box for the x,y and z extents.

I am not in a position to be able to write a fix right away as I have other tasks to complete, but if you can't get to it hopefully next week I'll have a chance to look at it.

Cheers,

Robert.

 

[Guy Volckaert]

If I have a chance, I'll try to look at it as well based on your suggestion solution.

Cheers,
Guy

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Read this topic online here:

http://forum.openscenegraph.org/viewtopic.php?p=72217#72217