Adobe After Effects CS4 - Manual (Page 571)

565 USING AFTER EFFECTS CS4
Effects and animation presets
Last updated 12/21/2009
With the Grid, a new particle appears on every frame at each grid intersection. You can’t adjust this frequency, but if
you want to turn off the Grid or make the Grid stop generating particles at specific times, set the Particle Radius/Font
Size control to 0, or use keyframes to animate the value of the Particles Across and Particles Down controls. To make
more particles appear in each frame, increase the values for Particles Across and Particles Down.
Note: By default, the Cannon is on and the Grid is off. If you are using the Grid and want to stop the Cannon from
generating particles, turn off the Cannon by setting its Particles Per Second value to 0.
Position Specifies the (x,y) coordinates of the grid center. When a grid particle is created, it is centered over its grid
intersection, regardless of whether it is a dot, a layer, or a text character. If you’re using text characters as particles, the
Use Grid option in the Edit Grid Text dialog box is on by default, placing each character on its own grid intersection,
so normal character spacing, word spacing, and kerning do not apply. If you want text characters to appear at the grid
position with normal spacing, use a text alignment other than the Use Grid option.
Width, Height Specify the dimensions of the grid, in pixels.
Particles Across, Particles Down Specify the number of particles to distribute horizontally and vertically across the grid
area. Particles are generated only when the value is 1 or more.
Note: If the Width, Height, Particles Across, and Particles Down controls are not available, the Use Grid option has been
turned off in the Edit Grid Text dialog box.
Color Sets the color of dots or text characters. This control has no effect if you use a layer as the particle source.
Particle Radius/Font Size Sets the radius of dots in pixels or the size of text characters in points. This control has no
effect if you use a layer as the particle source.
Layer Exploder and Particle Exploder
The Layer Exploder explodes a layer into new particles, and the Particle Exploder explodes a particle into more new
particles. In addition to explosion effects, the exploders are also handy for simulating fireworks or for rapidly
increasing the number of particles.
The following guidelines can help you control particles resulting from an explosion:
• A layer is exploded once for each frame. By default, this creates a continuous shower of particles for the duration
of the composition. If you want to start or stop a layer explosion, animate the Radius of New Particles control by
using keyframes so that its value is zero at times when you don’t want particles to be created.
• If the source of the layer is a nested composition, you can set different Opacity values or In and Out points for the
layers within the nested composition to make the exploding layer transparent at different points in time. The Layer
Exploder does not create particles where the source of the layer is transparent.
• To change the position of the exploding layer, precompose the layer with its new position (use the Move All
Attributes Into The New Composition option), and then use the precomposed layer as the exploding layer.
• When you explode particles, the new particles inherit the position, velocity, opacity, scale, and rotation of the
original particles.
• After layers or particles explode, Gravity, Repel, Wall, and Property Mapper controls influence the movement of
particles.
Some Persistent Property Mapper and Ephemeral Property Mapper options can make explosions more realistic.
For example, change Opacity to make the resulting particles fade out, or change the Red, Green, and Blue color
channels to make resulting particles change color as they appear to cool.
Explode Layer (Layer Exploder only) Specifies the layer you want to explode. To make the video disappear the
moment the particles appear, either turn off the video for the layer or trim the Out point of the layer.