[Plib-users] <<Code review>> ssgEntity::isectTest ( sgSphere *s, sgMat4 m, int testNeeded )

[Rahul C. <rah...@ya...>]

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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