Hi Tanguy,
What makes you think its wrong ? I think its very smart code which does only
whats really neccessary. _lowerBBCorner and _upperBBCorner are not constant
and in fact are relative and precalculated based on plane orientation.
Depending on the plane orientation its possible to know before hand which
corners of axis aligned bounding box will represent most extreme points of the
box.
Cheers,
Wojtek
----- Original Message -----
From: Tanguy Fautre
To: OpenSceneGraph Users
Sent: Monday, October 19, 2009 3:25 PM
Subject: [osg-users] Plane::intersect(BoundingBox & box) buggy ?
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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