Graphics Programs Reference
In-Depth Information
Even though this is a very simple simula-
tion, it's still quite impressive! The Particle
Emitter begins generating a virtual water-
fall at frame 0. Then at frame 20, the
Collision object rams into it, sending parti-
cles flying. At frame 40, the Collision object
passes through the Emitter again, causing
particles to bounce off as it returns to its
starting point. You can see that the initial
impact of our Collision object causes the
particles to scatter farther than the second
impact. It's important to note that the speed
at which your Collision object moves has a
tremendous effect on the object it collides
with, just as it would in real life. Stop for a
moment and think about how long it would
take you to animate each of these particles
by hand. You'll begin to realize just how
powerful Dynamics can be!
The settings for a Collision object play a
large part in determining how it interacts
with other dynamic objects in your scene.
As we examine the remaining Dynamic
types, we'll spend more time talking about
Collision objects and their various settings.
For now, however, we'll wrap up this dis-
cussion with a few
helpful hints.
A collision occurs
when the points of an
object come in contact
with the polygons of
another object. If the
polygons (or edges )ofan
object collide with the
polygons (or edges )of
another object, the colli-
sion detection will fail.
For this reason, it's best
to have more points in
the object that collides
(often a personal
dynamic) and less
points in the object it collides with (the Col-
lision object).
The Collision property works best
when the object it's applied to is made up of
quads. If you find that the collision detec-
tion is failing, even on simple geometry, try
rebuilding the collision surface so that it is
comprised of four-point polygons.
Collision detection works differently
depending on the type of object you're
using. When the Collision dynamic is
applied to a regular polygonal object, a
bounding box will be used to determine the
collision area. This works well in some
cases, but not so well in others. Take, for
example, Figure 19-7. You would expect the
ball to fall through the hole in the ground,
but it won't. Instead, the ball will fall onto
the hole and bounce. To remedy this, we
need to convert the ground into a subpatch
object. Collision detection for subpatch
objects is determined by the actual shape of
the polygons in the object.
If you follow these hints, you should be able
to avoid most situations that cause collision
Figure 19-7
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