Exercise 3: One burst on demand

Purpose. To fire the sparks from Exercise 2 as a single burst, at the moment you choose.

Enabled gives a stream that runs until it is switched off. An impact, a muzzle flash or an explosion is the other kind of effect: it happens once and is over. The HUD fires that kind. It holds three numbers and one button.

Before starting

• The emitter from Exercise 2 is in the workspace and selected.
• Enabled is off.

Procedure

The three boxes are in the HUD, under the emitter’s name, labelled Emit, Delay and Duration. The Emit button is under them.

Step	Control	Action	Result
1	HUD ▸ Emit button	Press	One spark leaves and falls. The Emit box reads 1.
2	HUD ▸ Emit box	Enter 30	No change yet.
3	HUD ▸ Emit button	Press	Thirty sparks leave at the same instant, spread, and fall.
4	HUD ▸ Delay box	Enter 0.5	No change yet.
5	HUD ▸ Emit button	Press	The burst leaves half a second after the press.
6	HUD ▸ Duration box	Enter 2	No change yet.
7	HUD ▸ Emit button	Press	After the delay, the burst of thirty leaves. A stream at the emitter’s Rate follows it for 2 seconds, then stops by itself.
8	HUD ▸ auto-emit button (the icon to the right of Emit)	Press	The icon turns green. The whole effect replays, with a pause of one second after each play ends.
9	HUD ▸ auto-emit button	Press again	The replays stop.

NOTE

The Emit button fires exactly what the three boxes say. On a new emitter they read 1, 0 and 0, so one press makes one particle. See Emit count of 1.

NOTE

Auto-emit keeps replaying the items that were selected when it was switched on. Selecting something else does not change what it replays. Switch it off and on again to point it at a new selection.

What the numbers did

Emit is the size of the burst: the number of particles made at once when the button is pressed.

Delay is the wait, in seconds, between the press and the burst.

Duration is the length, in seconds, of the stream that follows the burst. During that time the emitter behaves as if Enabled were on, and makes particles at its Rate. At 0 there is no stream.

The three combine. Take Emit 30, Delay 0.5 and Duration 2. One press gives half a second of nothing, thirty particles at once, then two seconds of stream.

Emit	Duration	One press gives
0	0	Nothing
1	0	One particle. A new emitter starts here.
30	0	A burst of 30
0	2	A stream for 2 seconds, with no burst
30	2	A burst of 30, then a stream for 2 seconds

All three numbers are saved with the emitter, like the values in the Properties panel.

Auto-emit presses Emit for you. It waits until every particle of the last play has finished, waits one second more, and plays again. The length of that extra wait is AutoEmit Delay in Settings (≡, then Settings).

If the result differs

Symptom	Cause	Action
The Emit button does nothing	Emit and Duration are both 0.	Enter a number in one of them.
A typed value has no effect	The text was not a number. These three boxes do not flash red.	Enter the number again and press Enter.
The burst looks like one particle	SpreadAngle is 0, 0, so all thirty take the same line.	Set SpreadAngle as in Exercise 2.
Auto-emit replays the wrong effect	It was switched on with another selection.	Switch it off, select the emitter, switch it on.

Variations

Change	Result
Emit 200	A dense burst. All 200 count toward the Particle Cap.
Emit 0, Duration 3	Each press gives a three second stream and no burst.
The switch at the right of the HUD’s button row	It turns Enabled on or off for everything selected. With one emitter selected it is the same switch as the Enabled row in the Properties panel.
AutoEmit Delay 0.2 in Settings	Replays follow each other almost without a pause.

Log

New in this exercise	The Emit, Delay and Duration boxes. The Emit button. Auto-emit.
Done before	Selecting the emitter (Exercises 1 and 2). Everything the sparks do in flight (Exercise 2).
Carried forward	Leave auto-emit off. Exercise 4 starts with a new Part.