result_info compute_box_visibility(const vec3& center, const vec3& extent, const plane_info frustum[6], result_info in)
// Returns a visibility code indicating the culling status of the
// given axis-aligned box. The result_info passed in should indicate
// which planes might cull the box, by setting the corresponding
// bit in in.active_planes.
{
// if (in.culled) return in; // This check should be done by caller.
// Check the box against each active frustum plane.
int bit = 1;
for (int i = 0; i < 6; i++, bit <<= 1) {
if ((bit & in.active_planes) == 0) {
// This plane is already known to not cull the box.
continue;
}
const plane_info& p = frustum[i];
// Check box against this plane.
float d = p.normal * center - p.d;
float extent_toward_plane = fabsf(extent.get_x() * p.normal.get_x())
+ fabsf(extent.get_y() * p.normal.get_y())
+ fabsf(extent.get_z() * p.normal.get_z());
if (d < 0) {
if (-d > extent_toward_plane) {
// Box is culled by plane; it's not visible.
return result_info(true, 0);
} // else this plane is ambiguous so leave it active.
} else {
if (d > extent_toward_plane) {
// Box is accepted by this plane, so
// deactivate it, since neither this
// box or any contained part of it can
// ever be culled by this plane.
in.active_planes &= ~bit;
if (in.active_planes == 0) {
// This box is definitively inside all the culling
// planes, so there's no need to continue.
return in;
}
} // else this plane is ambigious so leave it active.
}
}
return in; // Box not definitively culled. Return updated active plane flags.
}
plane_class classify_point( const plane_info& p, vec3 a, float slop )
// Classify the given point with respect to the given plane; use a tolerance
// of +/- slop to determine when a point is ON the plane.
{
float distance = p.normal * a - p.d;
if ( distance < -slop ) {
return INSIDE;
} else if ( distance > slop ) {
if ( print_debug ) {
printf( "d = %f, pn = %f %f %f, pd = %f, a = %f %f %f, p*a = %f\n",
distance, p.normal.get_x(), p.normal.get_y(), p.normal.get_z(), p.d,
a.get_x(), a.get_y(), a.get_z(),
p.normal * a
); //xxxx
}
return OUTSIDE;
} else {
return ON;
}
}
