Adobe After Effects CS4 - Manual (Page 572)

566 USING AFTER EFFECTS CS4
Effects and animation presets
Last updated 12/21/2009
Radius Of New Particles Specifies the radius of the particles resulting from the explosion. This value must be smaller
than the radius of the original layer or particle.
Velocity Dispersion Specifies, in pixels per second, the maximum speed of the range within which Particle Playground
varies the velocity of the resulting particles. High values create a more dispersed or cloudlike explosion. Low values
keep the new particles closer together and can make the exploded particles resemble a halo or shockwave.
Affects Specifies which particles the Layer Exploder and Particle Exploder affect.
Layer Map controls
By default, the Cannon, Grid, Layer Exploder, and Particle Exploder create dot particles. To replace the dots with a
layer in the composition, use the Layer Map. For example, if you use a movie of a single bird flapping its wings as a
particle source layer, After Effects replaces all dots with an instance of the bird movie, creating a flock of birds. A
particle source layer can be a still image, a solid, or a nested After Effects composition.
A multiframe layer is any layer with a source that varies over time, such as a movie or a composition. When you map
new particles to a multiframe layer, use the Time Offset Type control to specify how you want to use the frames of the
layer. For example, use Absolute to map an unchanging image onto a particle, or use Relative to map an animating
sequence of frames onto a particle. You can randomize both Absolute and Relative across particles.
Note: When you choose a layer for Layer Map, Particle Playground ignores any changes that you made to that layer
within that composition. Instead, it uses the layer in its original state. To keep transformations, effects, masks,
rasterization options, expressions, or keyframe changes for a layer when you use it as a particle source, precompose the
layer.
Use Layer Specifies the layer you want to use as the particles.
Time Offset Type Specifies how you want to use the frames of a multiframe layer. For example, if you are using a layer
of a bird flapping its wings and you choose Relative for Time Offset Type with a Time Offset of 0, the flapping wings
for all the instances of the bird are synchronized. While this may be realistic for a marching band, it is not realistic for
a flock of birds. To make each bird start flapping its wings from a different frame in the layer, use Relative Random.
• Relative Starts playing the layer at a frame based on the Time Offset you specify, relative to the current time of the
effect layer; then advances in step with the current time of the Particle Playground layer. If you specify a Time Offset
of 0, all particles show the frame that corresponds to the current time of the effect layer. If you choose a Time Offset
of 0.1 (and your composition is set to 30 fps), each new particle displays the frame that is 0.1 seconds after the previous
particle’s frame. Regardless of the Time Offset you specify, the first particle always displays the frame of the source
layer that corresponds to the current time of the effect layer.
• Absolute Displays a frame from the layer based on the Time Offset you specify, regardless of the current time.
Choose Absolute when you want a particle to show the same frame of a multiframe source layer for its entire lifespan,
instead of cycling through different frames as the effect layer advances in time. For example, if you choose Absolute
and specify a Time Offset of 0, every particle shows the first frame of the source layer for its entire lifespan. If you want
to show a frame other than the first frame, move the layer earlier in time until the frame you want to show corresponds
to the In point of the Particle Playground layer. If you specify a Time Offset of 0.1, for example, each new particle
displays a frame that is 0.1 second after the frame of the previous particle (or every third frame of a 30-fps animation).
• Relative Random Starts playing the layer from a frame chosen at random, within the range between the current
time of the effect layer and the Random Time Max you specify. For example, if you choose Relative Random and
specify a Random Time Max of 1, each particle starts playing from a layer frame chosen at random from between the
current time and 1 second after the current time. If, for another example, you specify a negative Random Time Max
value of - 1, the Random Time Max is before the current time, so that the range within which new particles start playing
advances as the current time advances. However, the range is always between the current time and one second earlier
than the current time.