I was just going through the code of SSG and saw
something interesting in the following:
ssgCullResult ssgEntity::isectTest ( sgSphere *s,
sgMat4 m, int testNeeded )
In the above member function you are
finding out the delta distances (in x, y and z
direction) between the centers of two
spheres and trying to see whether delta
distance in any direction is greater
than the sum of the radii.
The code currently looks like:
sgVec3 center_vec ;
float sum_radii = s->getRadius() + tmp.getRadius() ;
sgSubVec3 ( center_vec, s->getCenter(),
tmp.getCenter() ) ;
if ( center_vec[0] > sum_radii ||
center_vec[1] > sum_radii ||
center_vec[2] > sum_radii ) {
return SSG_OUTSIDE ;
}
I think the last line should be modified to
take absolute values of center_vec[0],
center_vec[1] and center_vec[2]
Next thing ssg code does is taking squares
of each of the radius, adding them and
compares them with the square of the
distances between the centers
Or in other words, it says
if d^2 >= radiousOne^2 + radiousTwo^2
then the given sphere lies outside the
entity. (here d is the distance
between the two centers of spheres,
radiousOne is the radius of the
entity sphere and radiousTwo is the
radius of second sphere).
In stead I think we should say
if d^2 >= (radiousOne + radiousTwo)^2
or d >= (radiousOne + radiousTwo)
then the given sphere lies outside the
entity.
In other words the distance between the
center of two spheres should be more
than or equal to the summation of radii
of two spheres for the sphere to be
disjoint.
Please let me know your thoughts on this.
-- Rahul
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