9

Shape Facing Operator 177
Inter face
Look At Cam era/Object group
Use this cont rol for defining the camera or object
toward which the particle will face. This object is
known as the Look At object.Forthetechnically
minded, the facing is maintained by keeping each
particle’s local Z axis pointed at the Look At object,
or when Use Parallel Direction is on, aligned with
the vector b etween the Particle Source icon and
the Look At object.
Name—After picking a Look At object, its name
appears here.
Pick Camera or Object—Click this button, and then
selectacameraorobjectinthescenetouseasthe
Look At object. The mouse cursor changes to a
cross shape when positioned over a valid object.
Use Par allel Direction—When off, al l particles
continuously rotate to stay facing toward the
Look At object. Each particle’s orientation varies
because its location differs from those of the
others. When on, all particles face in the same
direction, defined by an ima ginary line between
theParticleSourcegizmocenterandtheLookAt
object. Default=off.
Size/Width group
Use these settings to specify the coordinate system
for setting the size, as well as the s ize parameters.
The numeric settings in this group are not
animatable.
In World Space—Setstheabsolutesizeinsystem
units, using the World coordinate system.
Units—With the In World Space option, sets
theparticlesizeinsystemunits. Range=0to
1000000000. Default=1.
In Local Space—Sets particle size relative to the
existing size, in local space. The software uses the
dimensions of the existing shape to determine the
size of the “facing rectangle.”
Inherited % —Sets the facing particles’ size as a
percentage of the existing size. Range=0 to 100.
Default=100.
In Screen Space—Sets the facing par ticles’ size as
apercentageofthescreenwidth.Theactualsize
of each particle changes as necessary throughout
the animation, depending its distance from the
camera, to maintain a constant size from the
camera’s point of view.
This option is available only when the Look At
object is a camera, and Use Parallel Direction is off.
Propor ti on % —Sets the particle size a s a percentage
of the screen w idth. Default=1.