Particle
View 
Click Collision in an event or add Collision
to the particle system and then select it.
Collision tests for
particles that collide with one or more specified Deflector space
warps. It can also test whether a particle has slowed down or sped
up after one or more collisions, has collided more than once, and
even whether it will collide with a deflector in a specified number
of frames.
The Collision test supports
all deflector space warps except the DynaFlect deflectors:
TipWhen testing for
collisions with multiple deflectors, for best results, place all
the deflectors in a single Collision test. This tests for collisions
with all the deflectors simultaneously, and helps avoid possible
missed collisions.
Procedures
Example: To test for particles slowing
down after one or more collisions:
In the real world, particles
bouncing repeatedly against a surface lose kinetic energy at each
collision, and slow down gradually. Rather than testing for a specific
number of bounces, you can use the Is Slow After Collision(s) to
test whether particle speed has sunk below a specific level.
- Start or reset 3ds Max. Set the animation
length to 500 frames.
- Add a Gravity space warp and a Deflector
space warp. Decrease the deflector's Bounce setting below 1.0, and
increase the Variation and Chaos values above 0.0. Set the deflector's
Width and Length to 500.
- Create a default Particle Flow system.
Position the emitter directly above the deflector.
- Add a
Force
operator to the end of Event 01 and add
the Gravity space warp to the Force operator.
- Create a new event with a
Display
operator, and change the display type
to a different choice than is used in Event 01.
- Add a Collision test to Event 01, below
the Force operator, and wire it to the new event.
- In the Collision test settings, add the
deflector. Choose Is Slow After Collision(s), and set Speed Min=100 (assuming
you're using the default initial speed of 300).
-
Play
the animation. You might need to adjust one or more settings before
seeing the expected behavior.
After several bounces,
the particles change in appearance and move steadily away from the
deflector, indicating that they've entered the second event. Of
course, you can set any behavior you like in this event.
In the next step, you'll
see what happens when actions in an event are not in the right order.
- In Event 01, move the Collision test
above the Force operator, and then play the animation.
Quite a few particles
leak through the deflector. This happens because Particle Flow first
tests the particles for a collision, and then applies the Gravity
force. The particles that are approaching the deflector and are
very close to it are being tested for a collision, which tests False because
they haven't actually struck the deflector yet. Particle Flow then applies
the gravity, which pushes them past the deflector, making them no
longer eligible for testing for collision. Generally speaking, it
is best to keep Force operators above Collision tests in each event
to ensure that particles don't leak through the deflector.
Interface
The user interface appears
in the parameters panel, on the right side of the Particle View
dialog.
Deflectors group
This group displays the
deflectors currently in effect, and let you add and remove deflectors.
- [list]
-
Shows the deflectors
that apply to this operator. If more than three deflectors apply,
a scroll bar appears at the right side of the list.
If you delete a listed
space warp from the scene, its name is replaced in the list by the entry “<deleted>”.
- Add
-
Click this button, and then
select a Deflector space warp in the scene to add it to the list.
- By List
-
Click this button, and then
use the Select Deflectors dialog to add one or more space warps
to the list. The space warps must already exist in the scene.
- Remove
-
Highlight a deflector
in the list, and then click this button to remove it from the list.
Any removed space warps remain in the scene.
Test True If Particle group
Choose the condition
under which the test will pass particles on to the next event, and
then adjust the associated setting or settings. Default=Collides.
- Collides
-
Choose this option, and then
set Speed according to how particle speed should be affected by
the collision.
- Speed
-
Choose one of the following.
Default=Bounce.
- BounceThe
speed and direction after collision is determined by the deflector properties.
- ContinueParticle
speed and direction are unaffected by the collision.
- StopParticle
speed is set to 0 after the collision.
- RandomParticles
bounce off the deflector in random directions.
- Is Slow After Collision(s)
-
The test succeeds if,
after collision, particle speed is less than the Speed Min value.
With this choice, particle
behavior with respect to the deflector(s) is the same as with the
Collides Bounce option.
- Speed Min
-
Particles traveling at
less than this speed, in system units per second, test True and
become eligible for moving to the next event. Default=1.0.
- Is Fast After Collision(s)
-
The test succeeds if,
after collision, particle speed is greater than the Speed Max value.
With this choice, particle
behavior with respect to the deflector(s) is the same as with the
Collides Bounce option.
- Speed Max
-
Particles traveling faster than
this speed, in system units per second, test True and become eligible
for moving to the next event. Default=1000.0.
- Collided Multiple Times
-
The test becomes True after
a particle collides a specific number of times. The particle is
moved to the point of the last collision and then redirected to
the next event.
- # Times
-
The number of times a particle
must collide in order to test True.
- Speed
-
Determines speed and direction
after the specified number of collisions. See above for explanations
of the choices.
- Will Collide
-
Particle Flow extrapolates particle
motion in a linear fashion, based on the current direction and speed,
and the test becomes True if the results suggest that the particle
will collide with the deflector during a specified time interval.
The particle is redirected to the next event without updating its
speed or position.
- # Frames
-
The number of frames ahead
during which Particle Flow looks for an impending collision.
Uniqueness group
The Uniqueness setting
enables randomization of the Random options in the Speed drop-down
lists.
- Seed
-
Specifies a randomization value.
- New
-
Calculates a new seed using
a randomization formula.
