9

Shape Mark Operator 183
New—
Calculates a new seed using a randomization
formula.
Shape Mark Operator
Particle View (page 2–125) > Click Shape Mark in an event
or add a Shape M ark operator to the par ticle system and
then select it.
UsetheShapeMarkoperatortoreplaceeach
particle with either a rectangle or a box cut out
from the particle geometry with an image mapped
onto it. The image can be animated and the
animation can be sy nchronized with particle
events.
A typical application of Shape Mark would be to
leave marks after particles impact objects in the
scene. For example, when a torpedo 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 2–186) inthesameeventwith
transparent areas to define the mark’s outline.
For example, apply a Mask map to the material’s
Opacity channel, and to the map’s Mask channel,
apply a bitmap containing an alpha channel. On
the Bitmap Parameters rollout, set Mono Channel
Output to Alpha.
Note: With its default settings, the Shape Mark
operator can generate coplanar faces, which the
mental ray renderer cannot render well. If you
want to use mental ray rendering with Shape Mark,
adjust the operator’s settings as follows:
• In the Shape group, cho ose Box Intersection.
• Set Surface Offset to 0.01.
• Set Offset Variation to 0.005.
• Set Vertex Jitter to 0.002.
With these settings, faces are no longer coplanar,
and the mental ray renderer gives better results.
See also
Shape Operator (page 2–176)
Shape Instance Operator (page 2–178)
Shape Facing Operator (page 2–176)
Procedure
Ex ample: To use Sha pe Ma rk :
1.
Determine which object is to receiv e the marks;
this wil l be the contact object. Apply a deflector
to this object.
2. Set up your par ticle system with an event that
causes particles to collide with the contact
object deflector.
3. At t he end of this event, add a Collision test
(page 2–212).
4. In the 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 necessary.
Now, when the particles strike the contact
object, they disappear, le aving marks on the
object.
If you want the particles to bounce after leaving
marks, rather than disappearing, use a Collision
Spawn test (page 2–215) instead, and t urn off its
Delete Parent check box. The spawned particles
become the mark s, and the orig inal particles
remain in the first event.
7. Optionally, add a Material operator to define
the surface characteristics of the marks.