8

Go To Rotation Test 221
To set a target orientation, place the Go To
Rotation test
before an orientation-type operator
(
Rotation (page 2–149) or a Script operator (page
2–204)
if it defines the rotation channel) in the
same event. In this situation, the Go To Rotation
test can grab the particle rotational component
beforetheorientation-typeoperatoroverwritesit.
The Go To Rotation operator modifies the particle
orientation and spinning in the post-evaluation
cycle. For an example, see the procedure below.
Wa rn in g : The G o To Rotation test is n ot compatible with
the Spin, Shape Facing, and Shape Mark operators. Do
not use any of these operators in the same event with a
Go To R otation test.
Note:
You can define the tra nsition period only in
terms of time. You cannot set the test to come to a
specific rotation by the time of another test, such
as a collision test. Also, limited control is provided
over the axis of spinning when a particle comes to
the final rotation.
Procedure
Example: To mak e falling particles land smoothly,
face up:
This procedure assumes a basic knowledge of
Particle Flow usage.
1. In the Perspective viewpor t, add a Part icle Flow
system and r aise its icon about 80 units on the
Zaxis.
2. In Event 01, make the follow ing changes:
• Birth > Amount=50
• Speed=100
• Shape=Cube(oruseShapeInstancewith
acustomobject,suchasacoin-shaped
cylinder)
• Display > Type=Geometry
Thisreducesthenumberofparticlesandslows
them down, making it easier to see what’s going
on.
3. Add a Spin operator (page 2–150) to Event 01,
and set both Spin Rate and Variation to 150.
This gives the particles random spinning
behav ior as they fall.
4. Add an Age test to the end of Event 01, and set
Test Value=15.
This allows each particle to fall and tumble for
15 f rames before Go To Rotation takes effect.
5. From the Depot, drag a Go To R otation
test to an empty area in Event Display. Set
Durat ion=15 and keep all other default settings.
6. Insert a Rotation operator immediately after
theGoToRotationtest. ChooseRandom
Horizonta l as the orientation matrix. Keep the
other default settings.
TheGoToRotationtestwillusethisasthefinal
orientation for the particles.
7. Use a Speed event to create a third event. Set
Speed=0.0.
This stops the particles at the end of t he
animation.
8. In both new events, set Display >
Type=Geometry.
9. Wire the Age Test in Event 01 to Event 02, and
then wire the G o To Rotation test in Event 02 to
Event 03.
10. Play the animation.
The p articles tumble chaotically as they fall for
about 30 frames, and then come to a smooth
stop, facing up.