Linking the rate to particle life

How many particles an emitter needs to emit depends on how long they live. The rate of the percentage-based generators is measured in percent of the emitter's capacity per second, and the rule of thumb is simple: rate = 100 / life. Particles that live 2 seconds need a rate of 50 %, so that the emitter refills exactly as fast as its particles die.

The Emitter Guide can keep that relation for you. The link button on the title bar of the Termination section ties the generator rate to the Max Lifetime value: change the life, and the rate follows.

The button

The link button sits on the right of the Termination title bar, next to the section's … menu. It has three states:

• On (highlighted, linked chain icon). The rate is derived from the particle life. In the Generation section the rate shows the computed number, but its editors are disabled; hover the rate to see why.
• Off (broken chain icon). The rate is yours to edit; the life does not touch it.
• Unavailable (greyed out). The link cannot work with the current setup. The button's tooltip names the reason (see When the link breaks).

Click the button to switch between On and Off. Turning the link on is a regular editor action: Undo turns it off again and restores the previous rate.

New emitters start with the link on — their defaults already agree (a 2-second life and a 50 % rate). Effects saved by earlier editor versions open with the link off, so nothing in them changes until you turn it on.

How the rate is computed

EvenRing uses the maximum because it spaces particles evenly around a ring of slots: a slot may only be reused once the longest-living particle in it has died.

The particle life can be any of these value types:

• Fixed — the value itself is both the mean and the maximum. A life of 4 s gives a rate of 25 %.
• Random — the mean is the middle of the range, the maximum is its upper end. A life between 2 s and 6 s gives 25 % for Periodic and Approx Rate (mean 4 s) and 16.67 % for EvenRing (maximum 6 s).
• Graph — the graph is sampled: the mean is the average of the curve over its whole range, the maximum is its highest point. A graph without a shift is required.

There is no upper limit on the computed rate: particles that live half a second give 200 %.

While the link is on, the rate is always a single Fixed value. Turning the link on replaces whatever the rate was before — a graph, a random range, an expression with several rows — by that one number. Turn the link off if you want to shape the rate yourself again.

If the life is momentarily zero or shorter than a millisecond (for example, while you type a new number), the link stays on and the rate keeps its last value.

Changing the number of particles

While the link is on, the rate cannot be edited — it always keeps the emitter about full. To emit more or fewer particles without changing how long they live, change the emitter's Max. num. particles (its capacity) instead: the rate is a percentage of it, so twice the capacity means twice the particles per second, with the same life.

Other terminators

The link reads only the Max Lifetime terminator. Other terminators — Path and Condition — can end particles earlier than their maximum life. The link does not know about that: particles then die sooner than the rate assumes, so fewer of them are alive at once and the emitter does not fill up. If that matters, check the result in the preview, or turn the link off and raise the rate by hand.

When the link breaks

The link needs:

• a generator with a rate: Periodic, Approx Rate or EvenRing;
• exactly one Max Lifetime terminator (Path and Condition terminators do not count);
• a particle life that is a single Fixed, Random or Graph value — no expression, no extra rows, no shifted graph;
• a valid Generation section, and for Periodic, a rate in percent (not a legacy absolute rate from an old effect — use Convert to % first).

If one of these stops being true while the link is on — you switch the generator to By distance, add a second Max Lifetime terminator, paste a Generation section without a rate, or turn the life into an expression — the link turns itself off and the editor shows a notification naming the reason. It does not turn back on by itself when the setup becomes valid again: click the button when you want it back.

Switching between Periodic, Approx Rate and EvenRing keeps the link on; the rate is recomputed with the formula of the new generator.

Reflected emitters

On a reflected emitter the link follows its source emitter: the button is disabled and shows the source's state, and the rate comes from the source. A rate you overrode on the reflection earlier stays overridden until you discard the override.