Adobe AFTER EFFECTS 5.5 Help Manual page 370

Adobe After Effects Help
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Using a layer map to specify particles affected by a Property
Mapper (PB only)
In both the Persistent and Ephemeral Property Mappers, you can use the layer map's alpha
channel to make more subtle changes to the value of a particle property. For example,
particles over a layer-map pixel in which the alpha channel value is 255 are fully affected,
while lower values affect particles less. Layer-map pixels that are completely transparent
have no effect on particle properties. For more information, see "About layer maps (PB
only)" on page 374.
Note: As with other sets of options in Particle Playground, you can also use the Affects
options in both the Persistent and Ephemeral Property Mappers to narrow the set of
particles that are affected. See "Using Affects options to specify particles (PB only)" on
page 372.
When you set any of the following properties, Particle Playground copies the value from
the layer map (that is, the layer selected in the Use Layer as a Map menu) and applies it to
the particle.
None Modifies no particle property.
Red Copies the value of the particle's red channel within a range of 0.0–1.0.
Green Copies the value of the particle's green channel within a range of 0.0–1.0.
Blue Copies the value of the particle's blue channel within a range of 0.0–1.0.
Kinetic Friction Copies the amount of resisting force against a moving object, typically
within a range of 0.0–1.0. Increase this value to slow down or stop moving particles as if
braking.
Static Friction Copies the amount of inertia that holds a stationary particle in place,
typically within a range of 0.0–1.0. At zero, a particle will move when any other force, such
as gravity, is present. If you increase this value, a stationary particle requires more of
another force to start moving.
Angle Copies the direction in which the particle points, in degrees relative to the
particle's original angle. The angle is easily observable when a particle is a text character or
a layer without radial symmetry.
Angular Velocity Copies the velocity of particle rotation in degrees per second. This
determines how fast a particle rotates around its own axis.
Torque Copies the force of particle rotation. The angular velocity of a particle is increased
by a positive torque and is increased more slowly for particles of greater mass. Brighter
pixels affect angular velocity more forcefully; if enough torque is applied against angular
velocity, the particle starts spinning in the opposite direction.
Scale Copies the scale value of a particle along both the X and Y axis. Use this to stretch a
particle proportionally. A value of 1.0 scales the particle to its full size; a value of 2.0 scales
it 200%, and so on.
X Scale/Y Scale Copies the scale value of a particle along the X or Y axis. Use these to
stretch a particle horizontally or vertically.
X/Y Copies the position of a particle along the X or Y axis in the frame, in pixels. A value of
zero specifies a position at the left of the frame (for X) or at the top of the frame (for Y).
X Speed/Y Speed Copies the horizontal speed (X-axis velocity) or vertical speed (Y-axis
velocity) of a particle in pixels per second.
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