Hi,
I've used an osg::Polytope to test whether a given convex volume was
colliding against a BoundingBox. Unfortunately it wouldn't work. I've
tracked the problem down to Plane::intersect().
/** intersection test between plane and bounding sphere.
return 1 if the bs is completely above plane,
return 0 if the bs intersects the plane,
return -1 if the bs is completely below the plane.*/
inline int intersect(const BoundingBox& bb) const
{
// if lowest point above plane than all above.
if (distance(bb.corner(_lowerBBCorner))>0.0f) return 1;
// if highest point is below plane then all below.
if (distance(bb.corner(_upperBBCorner))<0.0f) return -1;
// d_lower<=0.0f && d_upper>=0.0f
// therefore must be crossing plane.
return 0;
}
The piece of code above assumes that the plane is axis aligned and that
the normal is pointing toward the positive part of the axis. Such an
assumption is wrong for most other planes, and certainly does break
osg::Polytope implementation (from what I understand). I had to bypass
it with the following (note that in my case I only needed a Boolean
returned value).
bool intersect(const osg::Plane & plane, const osg::BoundingBox & bb)
{
if (plane.distance(osg::Vec3(bb.xMin(), bb.yMin(), bb.zMin())) <=
0)
return true;
if (plane.distance(osg::Vec3(bb.xMin(), bb.yMin(), bb.zMax())) <=
0)
return true;
if (plane.distance(osg::Vec3(bb.xMin(), bb.yMax(), bb.zMin())) <=
0)
return true;
if (plane.distance(osg::Vec3(bb.xMin(), bb.yMax(), bb.zMax())) <=
0)
return true;
if (plane.distance(osg::Vec3(bb.xMax(), bb.yMin(), bb.zMin())) <=
0)
return true;
if (plane.distance(osg::Vec3(bb.xMax(), bb.yMin(), bb.zMax())) <=
0)
return true;
if (plane.distance(osg::Vec3(bb.xMax(), bb.yMax(), bb.zMin())) <=
0)
return true;
if (plane.distance(osg::Vec3(bb.xMax(), bb.yMax(), bb.zMax())) <=
0)
return true;
return false;
}
I wonder whether the OSG implementation is limited on purpose (in which
case it should be documented), or whether this is a real bug.
Cheers,
Tanguy
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