Niagara Tutorial: Expressions | UE Content Examples Reconstruction

1. Preparation

This is the effect we are going to make in this tutorial.

Note: The main content of this tutorial comes from the Content Examples that come with Unreal Engine

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Full Tutorials:

1. UE Niagara: Simple Sprite Emitter
2. UE Niagara: Simple Mesh Emitter
3. UE Niagara: Simple GPU Emitter
4. UE Niagara: Sprite Facing
5. UE Niagara: Blend Attributes By Value
6. UE Niagara: Static Beams
7. UE Niagara: Dynamic Beams
8. UE Niagara: Multiple Renderers
9. UE Niagara: Location Events
10. UE Niagara: Expressions

3. Introduction

Expressions are small snippets of HLSL that can be used to create micro behaviors inline in the stack without needing to create new modules.

In this example, no modules are used to influence the simulation, only direct setting of variables in conjunction with expressions and dynamic inputs.

4. Sim Target

Select Emitter Properties, set Sim Target to GPUCompute Sim, and check Fixed Bounds.

5. Spawn Rate

Click on the + sign to the right of the Emitter Update to add the Spawn Rate module.

Spawn Rate: Number of particles per second to spawn.

6. Spawn Rate

Set the Spawn Rate value to 1000.0.

Spawn 1000.0 particle per second.

7. Emitter Update Parameter

Add Set new or existing parameter directly module to the Emitter Update section.

8. Emitter Update Parameter

Add a Vector parameter.

9. Emitter Update Parameter

Rename this parameter to InitialPosition and set its value to Simulation Position.

10. Emitter Update Parameter

Add a Float parameter.

11. Emitter Update Parameter

Rename this parameter to ZOffset and set its value type to New Expression.

12. Emitter Update Parameter

Set ZOffset to sin(Emitter.Age)*56.

13. Remove Initialize Particles

Delete Initialize Particles module.

14. Set Parameter

Add Set new or existing parameter directly module to the Particle Spawn section.

15. Particle Spawn Parameter

Add a Vector parameter.

16. Particle Spawn Parameter

Rename this parameter to RandomVector and set its value type to New Expression, then set its value to normalize(((( rand(float3(1.0,1.0,1.0) ))) * 2 ) -1 )

17. Particle Spawn Parameter

With the same operation, adds a number of parameters to Particle Spawn:

Name: Lifetime
Type：float
expression: rand(1.5f) + 2.2f

Name：Position
Type: vector
Expression: Emitter.InitialPosition + Particles.RandomVector *rand(145.0f)

18. Particle Spawn Parameter

Name: SpriteRotation
Type: float - NormalizedAngle
Expression: rand(1.0f)

Name: SpriteSize
Type: Vector 2d - float
Expression: rand(2.5f) + 0.5f

19. Particle Spawn Parameter

Name: Velocity
Type: Vector
Expression:

cross(Particles.RandomVector, float3(0,8,0)) * (float3(0.0f, 0.0f, Emitter.ZOffset) *0.2f) + (-1.0f * normalize(Emitter.InitialPosition - Particles.Position)*20)

20. Set Parameter

Add Set new or existing parameter directly module to the Particle Update section.

21. Particle Update Parameter

Name: Color
Type: Linear Color
Expression:

Particles.NormalizedAge < 0.333 ? float4(1,0.1,0.1,1) : Particles.NormalizedAge < 0.575 ? float4(0.1,1,0.1,1) : float4(0.1,0.1,1,1)

Name: Position
Type: Vector
Expression: Particles.Position + float3(0, 0, ( sin(Engine.Time) * 0.3f ))

22. Particle Update Parameter

Name: SpriteSize
Type：Vector 2D
Expression: (1.0f - abs(Particles.NormalizedAge * 2.0f - 1.0f)) * 2.0f

Name: PhysicsForce
Type: Vector
Expression: 1-Particles.RandomVector * (length(Particles.Position - Emitter.InitialPosition)*0.25)

23. Particle Update Parameter

Note that the namespace for PhysicsForce needs to be located in Transient

24. Particle Update Parameter

With the same operation, adds a parameter to Particle Update:
Name: Position
Type: Vector
Expression:

Particles.Position.z > Emitter.InitialPosition.z - Emitter.ZOffset ? Particles.Position : float3(Particles.Position.x, Particles.Position.y, Emitter.InitialPosition.z - Emitter.ZOffset)

25. Solve Forces and Velocity

Add Solve Forces and Velocity module to the Particle Update section.

26. 🎉 Finish! 🎉

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