Emission and shape modules in Unity - Step-by-Step Execution

Concept Flow - Emission and shape modules

Start Particle System

↓

Emission Module

↓

Calculate Emission Rate

↓

Shape Module

↓

Determine Particle Spawn Position

↓

Spawn Particle

↓

Repeat per frame

The particle system starts, emission module sets how many particles to create, shape module decides where they appear, then particles spawn and the cycle repeats.

Execution Sample

Unity

var ps = GetComponent<ParticleSystem>();
var emission = ps.emission;
emission.rateOverTime = 10f;
var shape = ps.shape;
shape.shapeType = ParticleSystemShapeType.Cone;
ps.Play();

This code sets the particle system to emit 10 particles per second from a cone shape and starts the system.

Execution Table

Step	Action	Emission Rate	Shape Type	Particle Spawn Position	Output
1	Initialize Particle System	Default (varies)	Default (varies)	Default	No particles yet
2	Set emission.rateOverTime = 10	10 particles/sec	Default	Default	Prepare to emit 10 particles per second
3	Set shape.shapeType = Cone	10 particles/sec	Cone	Positions inside cone volume	Particles will spawn inside cone
4	Call ps.Play()	10 particles/sec	Cone	Positions inside cone volume	Particle system starts emitting
5	Frame 1: Emit particles	10 particles/sec	Cone	Random position in cone	Particles appear at cone positions
6	Frame 2: Emit particles	10 particles/sec	Cone	Random position in cone	More particles appear
7	Repeat emission each frame	10 particles/sec	Cone	Random position in cone	Continuous particle emission
8	Stop or disable system	0 particles/sec	Cone	No spawn	Emission stops

💡 Emission stops when particle system is stopped or emission rate set to zero

Variable Tracker

Variable	Start	After Step 2	After Step 3	After Step 4	After Step 5	Final
emission.rateOverTime	Default	10	10	10	10	10
shape.shapeType	Default	Default	Cone	Cone	Cone	Cone
particle spawn position	Default	Default	Inside cone	Inside cone	Inside cone (varies)	Inside cone (varies)

Key Moments - 3 Insights

Why do particles appear at different positions each frame even though the shape is fixed?

Because the shape module defines a volume (like a cone), particles spawn at random positions inside that volume each frame, as shown in execution_table rows 5 and 6.

What happens if emission.rateOverTime is set to zero after starting the system?

Emission stops immediately, so no new particles spawn, as shown in execution_table row 8.

Does changing the shape module after starting the system affect already spawned particles?

No, changing the shape affects only where new particles spawn, not existing ones, as seen between steps 3 and 5.

Visual Quiz - 3 Questions

Look at the execution table, what is the emission rate after step 3?

A 10 particles per second

B 0 particles per second

C Default emission rate

D Emission stopped

💡 Hint

Check the 'Emission Rate' column at step 3 in the execution_table.

At which step does the particle system start emitting particles?

A Step 2

B Step 4

C Step 1

D Step 8

💡 Hint

Look for the action 'Call ps.Play()' in the execution_table.

If the shape type is changed to Sphere after step 3, how would the particle spawn position change?

A Particles spawn at a single point

B Particles spawn inside a cone volume

C Particles spawn inside a sphere volume

D Particles stop spawning

💡 Hint

Refer to the 'Shape Type' and 'Particle Spawn Position' columns in the execution_table.

Concept Snapshot

Particle System Emission and Shape Modules:
- Emission module controls how many particles spawn per second.
- Shape module controls where particles appear (volume shape).
- Set emission.rateOverTime to control rate.
- Set shape.shapeType to control spawn area.
- Call Play() to start emitting particles.

Full Transcript

This visual execution shows how Unity's particle system uses emission and shape modules. First, the particle system is initialized with default settings. Then, the emission rate is set to 10 particles per second. Next, the shape module is set to a cone shape, which means particles will spawn inside a cone volume. When Play() is called, the system starts emitting particles at random positions inside the cone. Each frame, more particles spawn inside this volume. Emission stops when the system is stopped or the emission rate is set to zero. Variables like emission rate and shape type change step by step, affecting how and where particles appear. Key moments clarify why particles spawn at different positions and how changing settings affects emission. The quiz tests understanding of emission rate, start of emission, and shape effects.