Hey Everyone,
I have a quad geometry attached to an OSG billboard configured with
axial rotation. I'm using a custom IntersectionVisitor that inherits
from the osgUtil::IntersectionVisitor and implements the getEyePoint,
getDistanceToEyePoint and getDistanceFromEyePoint using the same logic
as the CullVisitor. All other functionality in IntersectionVisitor is
the same.
The normal for the billboard with no rotation is <0, 1, 0>, so the
bounding box for it is min = <-5, -0.01, -5> max = <5, 0.01, 5>. The
problem is that as I rotate around the billboard, the line segment never
gets transformed into the billboard's space. As a result, the
intersection is always incorrect unless the billboard is oriented to its
natural position.
I tried extending my IntersectionVisitor to have an
apply(osg::Billboard) that pushes the billboard's computed matrix, using
the eye position which is available to my visitor, but I can't seem to
get the code correct. I'm mostly guessing at how I should handle the
pushModelMatrix and pushClone methods, so maybe someone can tell me what
I'm doing wrong (efficiency aside)?
osg::Vec3 LodIntersectionVisitor::getEyePoint() const
{
// Const member access is not provided for get*Matrix for some insane
// reason, so cast away the const.
LodIntersectionVisitor* _this =
const_cast<LodIntersectionVisitor*>(this);
osg::Vec3 eye_point = eye;
if( _this->getViewMatrix() ) eye_point = eye_point *
osg::Matrix::inverse( *_this->getViewMatrix() );
if( _this->getModelMatrix() ) eye_point = eye_point *
osg::Matrix::inverse( *_this->getModelMatrix() );
return eye_point;
}
void LodIntersectionVisitor::apply(osg::Billboard& billboard)
{
if (!enter(billboard)) return;
for(unsigned int i=0; i<billboard.getNumDrawables(); ++i)
{
osg::ref_ptr<osg::RefMatrix> matrix = _modelStack.empty() ? new
osg::RefMatrix() : new osg::RefMatrix(*_modelStack.back());
billboard.computeMatrix( *matrix, getEyePoint(),
billboard.getPosition(i) );
pushModelMatrix(matrix.get());
// now push an new intersector clone transform to the new local
coordinates
push_clone();
intersect( billboard.getDrawable(i) );
// pop the clone.
pop_clone();
popModelMatrix();
}
leave();
}
Thanks,
Chase
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