2009

Interface
The user interface appears in the parameters panel, on the right side of the
Particle View dialog.
Emit Start The frame number at which the operator begins emitting particles.
Emit Stop The frame number at which the operator stops emitting particles.
NOTE The Emit Start and Emit Stop values are tied to the system frame rate. If
you change the frame rate, Particle Flow automatically adjusts the Emit values
accordingly. For example, if you set Emit Start to 120 and Emit Stop to 300 using
the default NTSC frame rate (30 fps), and then switch to PAL (25 fps) using the
Time Configuration dialog, you've reduced the frame rate to 5/6 of the original
value. Thus, Particle Flow automatically uses the same ratio to adjust the Emit
settings, resulting in an Emit Start value of 100 and an Emit Stop value of 250.
This allows the particle system to retain the timing you specify, no matter which
frame rate you use.
NOTE With Subframe Sampling off, such adjustments are rounded off to the
nearest integer frame number. With Subframe Sampling on, fractional frame values
that result from such adjustments will be used, but not displayed.
Amount To specify the total number of particles emitted by the operator,
choose Amount, and then set the quantity of particles.
Using the Amount option, the first particle is always emitted at the Emit Start
frame, and the last particle is always emitted at the Emit Stop frame. Particles
emitted between these endpoints appear at equal intervals within the emission
period. For example, if you set Amount to 3, the second particle is emitted
halfway through the emission period.
To determine the number of particles emitted per frame when using Amount,
divide the Amount value by the number of emission frames (Emit Stop-Emit
Start+1).
2846 | Chapter 14 Space Warps and Particle Systems