8

Shape Mark Operator 179
New—
Calculates a new seed using a randomization
formula.
Shape Mark Operator
Particle Vie w (p age 2– 1 21) >ClickShapeMarkinanevent
or add a Shape Mark operator to the particle system and
then select it.
UsetheShapeMarkoperatortoreplaceeach
particle with either a rectangle or a box cut out
from the part icle geometry with an image mapped
onto it. The image can be animated and the
animation can be synchronized with part icle
events.
A typical application of Shape Mark would be to
leave marks after particles impact objects in the
scene. For exa mple, when a torpe do hits a boat
and explodes, you could use Shape Mark to leave
scorch marks on the boat surface.
Tip: By default, the mark left by Shape Mark is
always rectangular, no matter w hat shape the
particles are. To leave a differently shaped mark,
choosetheShapegroup>Rectangleoption,and
use a
material (page 2–182) inthesameeventwith
transparent areas to define the mark’s outline.
For example, apply a Mask map to the material’s
Opacity channel, and to the m ap’s Mask channel,
apply a bitmap containing an alpha channel. On
the Bitmap Parameters rollout, set Mono Channel
Output to A lpha.
Note: With its default settings, the Shape Mark
operator can generate coplanar faces, which the
mental ray renderer ca nnot render well. If you
want to use mental ray rendering with Shape Mark,
adjust the operator’s settings as follows:
• In the Shape group, choose Box Intersection.
• Set Surface Offset to 0.01.
• Set Offset Var iation to 0.005.
• Set Vertex Jitter to 0.002.
With these settings, faces are no longer coplanar,
and the mental ray renderer gives be tter results.
See also
Shape Operator (page 2–172)
Shape Instance Operator (page 2–174)
Shape Facing Operator (page 2–172)
Procedure
Ex ample: To use S hape M ar k :
1.
Determine which object is to receive the marks;
this will be the
contact object . Apply a deflector
to this object.
2. Set up your particle system w ith an event that
causes part icles to collide with the contact
object deflector.
3. At the end of this event, add a Collision test
(page 2–208)
.
4. In t he Collision test, designate the deflector
from step 1.
5. Create a new event with the Shape Mark
operator , and wire the Collision test to this
event.
6. In the Shape Mark operator > Contact Object
group, designate the object from step 1. Change
the other Shape Mark settings as necessar y.
Now, when the particles strike the contac t
object, they disappear, leaving marks on the
object.
If you want the particles to bounce after
leaving marks, rather than disappearing, use
a
Collision Spawn test (page 2–211) instead,
and turn off its Delete Parent check box. The
spaw ned p articles b ecome the marks, and the
original particles remain in the first event.
7. Optionally, add a Material operator to define
the surface characteristics of the marks.