[osg-users] AutoTransform, ROTATE_TO_SCREEN and small feature culling

[Hartwig Wiesmann]

Hi,

I found a very old article covering this issue: https://www.mail-archive.com/osg-users@lists.openscenegraph.org/msg15948.html. In the meantime it seems to be that proposal (2) has been implemented and the AutoTransform's computeBound() method returns an invalid bounding sphere during the first cull traversal. Nevertheless, when checking in the example osgautotransform.cpp the bounding spheres (of the text messages) remain invalid. To check this I have added an update callback to the AutoTransforms that only checks the validity of the bounding sphere.

Now, if the bounding sphere remains invalid culling of the AutoTransform's children will not be correctly performed because the AutoTransform's isCullingActive method will always return false (bounding sphere is invalid).

To solve this issue I was thinking to add a ComputeBoundingSphere callback or an update callback to the AutoTransform. But this is not a good solution because in this case I have to calculate always a new bounding sphere as I do not have access to the node's "_boundingSphereComputed" flag.

Another solution is to patch the node's getBound() method that will set the flag "_boundingSphereComputed" only to true if a valid "_boundingSphere" exists. This sounds reasonable in any case:

Code:
        inline const BoundingSphere& getBound() const
        {
            if(!_boundingSphereComputed)
            {
                _boundingSphere = _initialBound;
                if (_computeBoundCallback.valid())
                    _boundingSphere.expandBy(_computeBoundCallback->computeBound(*this));
                else
                    _boundingSphere.expandBy(computeBound());

                _boundingSphereComputed = _boundingSphere.valid();
            }
            return _boundingSphere;
        }



But I do not know if this breaks anything.

Is there any other method to get a valid bounding sphere for the AutoTransform without sacrificing performance?

Thank you!

Cheers,
Hartwig

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