CollisionParabola into CollisionInvSphere

[hecris]

The algorithm basically combines CollisionSphere::intersects_parabola with CollisionInvSphere::test_intersection_from_segment:
Recursively divide the parabola into "close-enough" line segments and then test their intersection with the sphere using similar implementation to CollisionInvSphere::test_intersection_from_segment.
I included unit tests and you can use this as a visualizer (similar to @rdb 's test program for parabola-into-box):

from panda3d.core import *
# load_prc_file_data("", "notify-level-collide debug")

from direct.directbase import DirectStart
base.cam.set_y(-20)

parabola = CollisionParabola(LParabola((1, 0, 1), (1, 0, 0), (-1, 0, 0)), 0.0, 1.0)
into = CollisionInvSphere((-1, -1, -1), 3)

into_node = CollisionNode("into")
into_node.add_solid(into)
into_node.set_into_collide_mask(1)
into_np = render.attach_new_node(into_node)
into_np.show()

from_np_parent = render.attach_new_node("from-parent")

from_node = CollisionNode("from")
from_node.add_solid(parabola)
from_node.set_from_collide_mask(1)
from_np = from_np_parent.attach_new_node(from_node)
from_np.show()

handler = CollisionHandlerEvent()

base.cTrav = CollisionTraverser()
base.cTrav.show_collisions(base.render)
base.cTrav.add_collider(from_np, handler)

def update(task):
    if base.mouseWatcherNode.has_mouse():
        pos = base.mouseWatcherNode.get_mouse()
        from_np_parent.set_pos(pos[0] * 10, 0, pos[1] * 10)
    # print('')
    return task.cont

base.taskMgr.add(update)

base.run()

Suggestions are welcomed!

[rdb]

Sorry for the late review! Feel free to poke me regularly on Discord if I take a while to look at your PRs.

The surface normal should always point towards the center for an inverse sphere. You have it pointing away from the center. You can just flip the sign of that.

The surface point should always lie on the surface of the into object. In some cases it seems to go "inside" the inverse sphere. You can actually calculate the surface point by taking what you got for the normal and multiplying it by the radius, and adding it to the center.

The point you did calculate using the current math, you can set as the interior point, actually, using new_entry->set_interior_point(...).

[hecris]

Thanks @rdb ! Will make the changes soon.

[rdb]

Great, thanks a lot! Merged in 563ff75. For future reference, please configure your editor to strip extra spaces at the ends of lines.