Niagara

Posted on | In
Paradigm
Obsidian: [[04-01-01-U_FluidNinja Fluid Ninja]] [[16-01-01-VFX VFX]]

https://youtu.be/vOSXl7-2vd0 https://80.lv/articles/drawing-locations-to-a-render-target-in-unreal-engine-5-1/ https://youtu.be/3fW5xjiDm-A

Interaction spaces

  • Triangles - u must point to specific mesh in query
  • Phys Volumetric -
  • Scene Depth - 2d buffer, don’t penetrate behind first depth
  • Distance Fields -

Paradigm

  • Modules - graph paradigm
  • Emitters - stack paradigm
  • Systems - stack and Sequencer timeline

Calculation stages

System

  • Module usage flags
    • System Spawn Script - on system spawn
    • System Update Script -

Emitter

Do what system (optimal to set for multiple emitters) do or define.

  • Module usage flags
    • Emitter Spawn Script - once on spawn
    • Emitter Update Script - Tick

Particle

  • Module usage flags
    • Particle Spawn Script - on spawn
    • Particle Update Script - every frame
    • Particle Event Script - In response to event
    • Particle Simulation Stage Script -

Spawn

Update

Scripts

Dynamic Input scripts

Dynamic Input scripts by Usage flag:

Module

Use as module in particle emitter.
Read/Writes parameters will appear in module.
Can be used with: particle , emitter, system scripts
IN: Map OUT: Module

Dynamic Input

Use as expression in parameter value. Almost the same as creating modules, but can be selected and dropped into the stack without actually creating new modules. (extensibility for inheritance. Instead of acting on a parameter map, dynamic inputs act).
Can be used with: particle , emitter, system scripts
IN: Map OUT: Module

Function

Functions to use inside module.
IN: Input OUT: Output

Attributes

Name Space

Name Space R W Define Share within
PARTICLES. Particle Particle Persisted f2f Loaded as payload. Per-particle (@point)
INPUT. Y N   Module input. Use inside of module for promoted Parameters
Module Module Module Module expose a module input to the System and Emitter Editor
LOCAL. Module Module Not persist f2f Transient values. Truly local for function ! Transient values.
EMITTER. Emitter, Particle Emitter Persisted f2f Emitter instance / color ect…
SYSTEM. Y System Persisted f2f System
ENGINE. Y N Runtime for Niagara itself Fundamental Attribs from unreal
USER. Y N    
OUTPUT. N (An output in Particle Spawn cannot be accessed in Particle Update) Y Not persist f2f pay for calculate but not for adding it to emitter (parameter writes) useful helpers included in the modules which are not yet written to the particle payload, but are available for use.
TRANSIENT. from any module from any module Not persist f2f Local only to a given stack context (like Particle Update)

Name space modifiers:

Name Space R
.MODULE. insert module name as namespace so if u have x modules u have x different params
.INITIAL. initial value of attribute (from eg in particle spawn)

Particle attributes vs Transient outputs:

  • Transient - Not persist f2f and between stages, not written to the payload, which means they don’t cross stack boundaries and are recalculated from scratch every frame
  • Particles - Persisted f2f (memory and performance cost)

Orientation

Mesh

Set Orientation

Inexpensive constant rotation rate. (rotational drag, an option on the drag module) has no effect. set: Particles.MeshOrientation

Update Mesh Orientation Module -
Orient Mesh To Vector Module - Can be after solve forcces

Rotational Force

Paradigm which factors mesh scale, mass, density, and drag into the model. larger meshes have a tendency to resist rotation due to their mass, and rotational drag can be used to control the acceleration/deceleration. Transient.PhysicsRotationalForce

"Mesh Rotation Force" Module in Particle Update - Solve Rotational Forces and Velocity Solver -
Drag

Need “Initial Model Dimensions” and mass > “Calculate Size by Mass”

Rotational Velocity / Drag

Rotational Forces accumulate into a Particles.RotationalVelocity variable and persist from frame to frame. Here we give the particles an initial “kick”, by applying a Rotational Force and then applying those forces to the Rotational Velocity. We use this method as it factors mass into the initial rotational velocity.

This then gets solved by the solver in update, and rotational drag eventually slows the particles down.

If you want the initial “kick” to not factor in mass, you can use an “Add Rotational Velocity Module” to directy set a rotation speed.

Mesh Rotation Force Module in Particle Spawn - Apply Initial Forces Module

Inheret Velocity - In Update, magnify velocity of root (have limit) Static Mesh Velocity with sample static mesh - will have velo of mesh Normal Vortex velocity

Sprite

Orient Mesh along vector

Alignment

` Particles.SpriteFaceing` - is the vector variable which controls which direction a particle faces

SpriteAlignment
SpriteRotation

SpriteUVScale
SpriteSubimageIndex
(in particles.)

Velocity

[Add Velocity] / [Add Velocity from point] / [Add Velocity in cone]- in particle spawn (ever frame if in update)

Coordinates & Space

Simulation, World, Local
Mesh Tri Coordinates > Bary Coords

Physics

Solve Forces and velocity

Write to intrinsic properties

Choose whether or not to write to intrinsic properties

ENGINE.DelatTime    
ENGINE.OWNER.Position    
Emitter Local Space  
Masss Position  Previous.Position, Velocity, Previous.Velocity,
TRANSIENT.PhysicsDeltaTime
TRANSIENT.PhysicsDrag
TRANSIENT.PhysicsForce
  • (time) Fractional updates based on collision equations
  • (Init copy:)
  • TRANSIENT.PhysicsForce > LOCAL.PhysicsForce, OUTPUT.MODULE.IncomingPhysicsForce
  • PARTICLE.Velocity > OUTPUT.MODULE.Velocity
  • PARTICLE.Mass > LOCAL /
  • PARTICLE.Position > OUTPUT.MODULE.Position
  • copy to > PARTICLES.PRESOLVE
  • (Apply mass to phys)
    • (1/LOCAL.Mass) * LOCAL.PhysicsForce > LOCAL.PhysicsForce
  • (Apply forces to velo) (copy drag irrespective of Mass)
    • OUTPUT.MODULE.Velocity * LOCAL.DelatTime * LOCAL.PhysicsForce > OUTPUT.MODULE.Velocity
    • TRANSIENT.PhysicsDrag > OUTPUT.MODULE.IncomingPhys
  • limit velko and acc
  • (Apply velo to pos)
  • OUTPUT.MODULE.Velocity * LOCAL.DelatTime* OUTPUT.MODULE.Position > OUTPUT.MODULE.Position
  • [T] copy
  • OUTPUT.MODULE.Position/ > PARTICLE.Position/
  • Velocity > Velocity
  • If Forces/Drag have been converted to Velocity, zero out
  • [T] 0 > TRANSIENT.PhysicsForce / PhysicsDrag
PARTICLE.Position
PARTICLE.Velocity
Presolve pos, velo
Presolve physic forces
TRANSIENT.PhysicsDrag
TRANSIENT.PhysicsForce

Point Attraction Force

EMITTER.LocalSpace
PARTICLE.Position
PARTICLE.Velocity
TRANSIENT.PhysicsForce

…

TRANSIENT.PhysicsForce

Point Force

EMITTER.LocalSpace
PARTICLE.Position
TRANSIENT.PhysicsForce

…

OUTPUT.POINTFORCE.Withinrange
OUTPUT.POINTFORCE.NormalizedFallof
OUTPUT.POINTFORCE.NormalizedDistance
TRANSIENT.PhysicsForce

Limit Force

Drag

Acceleration, Avoid, Gravity, Line Attraction, Linear, Mesh Rot, Spring, Vector Noise, Vortex, Wind

Houdini Combine Forces

.
  • Copy
  • PARTICLES.NiagaraForce > TRANSIENT.NiagaraForce
  • 0 > TRANSIENT.PhysicsForce
  • Lerp
  • Lerp PARTICLES.Velocity or (PARTICLES.HOUDINI.Velocity or PARTICLES.HOUDINI.GoalPosition) > PARTICLES.Velocity
  • Apply
  • PARTICLES.NiagaraForce > TRANSIENT.PhysicsForce
PARTICLES.NiagaraForcesMultiplayer
PARTICLES.Velocity
TRANSIENT.PhysicsForce

Render

HLSL

Micro Expressions

  • /* Custom HLSL! */
  • sin(Emitter.Age *0.3) /2 +0.5 - 0-1 time x 0.3
  • cross(Particles.RandomVector, float3(0,8,0)) - cross
  • rand(1.5f) + 2.2f - random
  • length(Particles.Position - Emitter.InitialPosition) - length
  • saturate() - fast clamp 0-1
  • frac(Emitter.Age *0.3) - 0-1 loop in time x 0.3
  • float3(0.0f, 0.0f, Emitter.ZOffset) *0.2f) - Add Z
  • Particles.Position + float3(0, 0, (sin(Engine.Time) * 0.3f )) - Add Z sin to actual pos

.

  • float3(Particles.UV,0) - make vector from uvs
  • (Particles.Position-Particles.PreviousPosition)/Engine.DeltaTime - render velocity

.

  • Emitter.InitialPosition + Particles.RandomVector
  • Particles.NormalizedAge
  • Particles.Position - Emitter.InitialPosition

.

  • (1.0f-(abs((Particles.RibbonLinkOrder)-0.5f)*2.0f))*50.0f - Ribbon radious

Conditioning

Particles.NormalizedAge<0.3 ? float4(1,0.1,0.1,1):Particles.NormalizedAge<0.5 ? float4(1,1,1,1):float4(1,1,1,1)

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

Map Attributes

Time:

  • Engine. DeltaTime / InverseDeltaTime / Owner.TimeSinceRendered / RealTime
  • Emitter.Age
  • System. Age/ TickCount
  • Time -
  • Particles.Age -
  • Particles.NormalizedAge - 0-1
  • Particles.Lifetime -
  • Module.DeltaTime
  • Module.LifeTime
  • Module.LoopParticlesLifetime

Translation

  • Particles.Position - @P
  • Particles.Scale- @pscale (mesh)
  • Particles.SpriteSize- @pscale (sprite)
  • Particles.RibbonWidth - Ribbon width
  • Particles.Owner.Position /Rotation /Scale - Owner Transform

Physics

  • Particles.Mass
  • Particles.Velocity - @v
  • Particle.PreviousVelocity - @v
  • Engine.Owner.Velocity
  • Physics.Force
  • Physics.DeltaTime

Render

  • Particles.MaterialRandom - Float
  • Particles.Color - Linear Color
  • Particles.DynamicMaterialParameter - Vector 4
  • Particles.CameraOffset
  • Particles.UVScale

Tips

  • Niagara 16 params can send to material
  • U can access only depth buffer can read
  • Use: Inheritance. You can always reparent

Interfaces

The Kill Particles module at spawn - acts as a form of “Rejection Sampling”. We sample the texture and then kill the newly spawned particles on their first frame if the sampled texture alpha equals 0.

Because Interpolated Spawn is unchecked in the emitter properties, newly spawned particles do not run both their spawn and update scripts on the frame they were born, making this technique quite inexpensive.

Particles.VisibilityTag - Render Visibility - can change renderer dynamicly

Ribbons

`NiagaraRibbonRendererProperties` module.  


##### Ribbon Render

Ribbon - `Particles.RibbonFaceing`, `RibbonLinkOrder`, `RibbonTwist`  


##### more ribbons

`SetRibbonIDByExecOrder` - get the particles execution index, make a Niagara ID and assign the execution index to the ID index, and then set `Particles.RibbonID` in the Map with our new ID.

-

`Particles.RibbonLinkOrder` is the variable which determines how particles of a given `RibbonID` link up with each other.

The Spawn Beam module establishes the order based on the new particles as they are spawned in a burst, and assigns a new unique `RibbonID` to each new set of particles so they stay as separate beams instead of one large interconnected ribbon between all particles in the emitter.

From there, normal particle simulation takes over, and because the ribbon ID and link order are not changing from frame to frame, the beams stay stable.


## Events
push  
Will be 2.0! cause of fixed payloads (could be arbitrary )

Location Event

CPU

Leader emitter

Particle update

Generate Location Event

Follower emitter

Event Handler

Event Handler Properties - Event Handler
Recive Locaation Event - Event Handler

Which runs after the event is received. This needs to include a “Receive X Event” Module to handle the event, and then other modules can be placed inside to have additional effect on the particles which receive events, for example an additional location module to provide an additional offset from the received event position.

Attribute Reader

GPU
Spawn Particles From Other Emitter and Sample Particles From Other Emitter modules which utilize the Particle Attribute Reader. Listen to other emitter (events not push, but pull directly) - bats, flock, swarming bugs, Flight Orientation

Get by ID - niagara unique particle qttribute
Get Vector by index – get attribute (like Color) by Index (order particle responce)
Get Spawned ID at Index > Get Vector by ID

  • can use it on yourself every particle can ask of neighbour pos (phys line)
  • can integrate with otherforces (like cable component in niagara) and

newParticleAtributeReader

Constraints

Vector Fields

.fga
add an Acceleration Force module under our Sample Vector Field, and then bind the value SampleVectorField.SampledVector to the Acceleration value VectorFieldSize

http://andy.moonbase.net/archives/1499

Distance Field

Sample Distance Field

Collision

CPU

Expensive, should be used sparingly.

  • can optionally generate events using the “Generate Event” (Receive collision event)

Collision- Ray Traced Generate Collision Event

GPU

Direction and D-buffer sampling

  • can sample the scene depth, or the global distance field.

Collision- GPU Distance field / GPU Depth Buffer. Can be used at the end of particle update (before solvere) or special collision module.

Collision module

  • Place a Solve Forces and Velocity module at the end of particle update. Ensure that the “Write to Presolve Parameters” checkbox is set to true.

  • Place a Collision module in a final simulation stage.

The simulation stage should operate on “particles” and perform 1 iteration.

  • A second “Solve Forces and Velocity” module should be placed immediately after the collision module. That module’s “Write to Intrinsic Properties” Bool should be driven by [Transient]CollisionValid.

Neighbor Grid 2D GPU

Sampling image - value to sample the texture as if it were a UV.

Spawn Particles In Grid - Emiter up
Grid Location
Sample Texture

Neighbor Grid 3D

special position cash when a lot of particle need global comunication

PBD

Mesh Reproduction Static

Set position from static mesh
Set UV by Dynamic material

Mesh Reproduction Skeletal

initialize mesh reproduction

Particle Update

update mesh reproduction

Material

  • add Niagara mesh reproduce uv’s

Houdini Point Clouds

Houdini

Niagara ROP

Export pointcloud as: .hjson, .hbjson - bin quicker

  • i@id per particle same for one particle
  • f@time of pop-up / arrival time // just normalize time before export! check length from a to b and set time
  • @type group
  • @life Life set for first point
  • i@dead = 1
  • NID - niagara id attrib CREATED BY SAMPLE MODULES
    no Force ?

hardcoded attributes -

Unreal

Emitter Spawn

InitHoudiniPointCache - Initialize

.

W:  
emitter.Houdini.LastSpawnTime - 0.0  
emitter.Houdini.LastSpawnTimeRequest - 0.0  
emitter.Houdini.LastSpawnedPointID - 0  
emitter.Houdini.RestSpawnState - [V]

Emitter Update

SpawnParticleFromHoudiniPointCache - Spawn only

  • GetPointIDTospawnAtTime - create spawn data: deltaTime, InterpStart, Delat, Count


.

R:    
engine.DeltaTime
emitter.LoopedAge  

R/W:  
emitter.Houdini.LastSpawnTime - 0.0   
emitter.Houdini.LastSpawnTimeRequest - 0.0   
emitter.Houdini.LastSpawnedPointID - 0  
emitter.Houdini.RestSpawnState - [V]   

W:
emitter.Houdini.MaxIndex  
emitter.Houdini.MinIndex  
emitter.Houdini.ASpawnParticlesFromHoudiniPoinCache.SpawnData

Particle Spawn

SampleSpawnHoudiniPointCache - sample data not set! (similar to sample niagara mofules )

  • Creat NID - Particles.Houdini.NID: This is not the same value as the original ID attribute. This is the persistent Niagara ID that should be used for attribute lookups.
  • GetPoint...AtTime -
  • Transform... - Local to sim for: P, N, v

.

R:
engine.Owner.SystemLocalToWorld
engine.Owner.SystemLocalToWorldNoScale
engine.Owner.SystemWorldToLocal
engine.Owner.SystemWorldToLocalNoScale

emitter.Houdini.MinIndex   // optimistaion > NID
emitter.LocalSpace
emitter.LoopedAge

R/W:
particles.Houdini.NID   

W:
particles.Lifetime
particles.Houdini.Alpha   // f@Alpha
particles.Houdini.Color   // v@Cd
particles.Houdini.Impulse  // @impulse
particles.Houdini.Normal  // v@N
particles.Houdini.Orient // 4@orient
particles.Houdini.Position // v@P  
particles.Houdini.Pscale  // f@pscale  
particles.Houdini.Type  // type  
particles.Houdini.Velocity  // v@v

Particle Update

SampleHoudiniPointCachce

  • GetSampleIndexesForPointAtTime - get sample index and BlendAlpha
  • Get... - and LERP
  • NF Transform Vector (Local to Sim) + NF Initial Particle Postition (engine.Owner.Position)

.

R:

engine.Owner.SystemLocalToWorld
engine.Owner.SystemLocalToWorldNoScale
engine.Owner.SystemWorldToLocal
engine.Owner.SystemWorldToLocalNoScale

engine.Owner.Position

emitter.LocalSpace
emitter.LoopedAge
particles.Houdini.NID  
particles.Houdini.CSVIndex

W:
particles.Houdini.Color   // v@Cd
particles.Houdini.Force   //
particles.Houdini.Normal  // v@N
particles.Houdini.Orient // 4@orient
particles.Houdini.Position // v@P  
particles.Houdini.Velocity  // v@v
  • set particle.position > particle.Houdini.position - drag and assign houdini particle positiopn
  • set Color > vector and float > Particles.Houdini.Color
  • set KillParticles > (see custom script)
    CombineForce

Custom attributes script

New niagara module script: custom attributes:

Map get > [Get Vector Attribute By Name] > set Input.HoudiniCache

(in parameters) [EmiterAttribute] > Input.HoudiniCache >
[ParticleAttrbute] > Particles.int32 (right namespace add modify to: Particles.Houdini.NID ) [EmitertAttribute] > Emiter.Age

Houdini trigger

R:
`engine.DeltaTime` -
`emmiter.TimerActive`


R/W:
`emitter.DistanceToPlayer`
`emmiter.HoudiniCacheTime`
`emmiter.MoveToStartTime`
`emmiter.NiagaraForcesMultiplayer`
`emmiter.T3.Execute`
`emmiter.T4.Execute`
`emmiter.T5.TriggeredOnce`
`emmiter.TimeToRest`
`emmiter.TriggeredOnce`

W:
`emmiter.T1.Execute`
`emmiter.T2.Execute`
`emmiter.T5.Execute`
`emmiter.TriggerSomething`

Sources

Houdini niagara - ue plugin
Houdini Extras - ue plugin
UNREAL FOR ALL CREATORS zobacz - SideFx
2020 04 SideFx Niagara(frompluginContent) / Demo2020 (water Paul)
2020 11 SideFx - 2020 11 SideFx YT - to samo co wyzej
Unreal
2018 11
2020 04 Inside Unreal - Houdini workflows / paul / crowd / chains
2020 05 Unreal - Building advanced effects in Niagara Unreal Engine character
2020 05 Unreal talk Wyeth
2020 08 Unreal Fest Online 2020 dek kart
2020 11 Advanced Niagara Effects Inside Unreal - popcorn

RTVFX
Particle Location Module Mini Tutorial - Near Surface Location Mini Tutorial - Using splines for GPU particles - Spline Location Mini Tutorial - Rope Physics Mini Tutoria - Near Surface Location Mini Tutorial - Ribbon Trail Mini Tutorial - UE4 Niagara Audio Visualization (passing data from BP to Niagara) - RTVFX pack

tuts

Camera Interface

on gpu more control. on cpu only on simulate will work

input.newCameraquery > GetCameraProperties - gpu/cpu properties newCameraquerry > PropertiesGpu
get Field Of View
Get View Space Transform GPU - tarnsforms View Properties GPU (in input)

Audio Interface

AudioOsciloscope - Direct access to waveform. high/low freq 1:1 waveform mapping
AudioSpectrum - Buckets fft

Play Audio module

Occlusion

GPU Occlusion of point in time can do for point ()
NewOcclusionQuery -
Occlusion Factor With Circle / Rectangle GPU - compare to depth bufer

``` Future:

  • ray matching particle sprites/ meshes
  • accum light in particle
  • vdb