
# Sub Emitters

Starting from Babylon.js v3.2, you can create sub emitters which let you spawn a new particle from an existing particle. Each one of these spawned sub particle systems is totally independent from the parent.

**Note:** Sub emitters are NOT supported in GPU particles.

## How To Use Sub Emitters

The list of sub particle systems to be used as sub emitters is kept in an array and assigned top the new property `subEmitters` of the appropriate system. 

```javascript
// Create sub emitter
var subEmitter = new BABYLON.SubEmitter(subParticleSystem);
// Have the sub emitter spawn the particle system when the particle dies
subEmitter.type = BABYLON.SubEmitterType.END;
// Set the +Y direction of the sub emitter equal to the direction the particle is/was heading
subEmitter.inheritDirection = true;
// How much of the existing particles speed should be added to the emitter particles
subEmitter.inheritedVelocityAmount = 1;

particleSystem.subEmitters = [subEmitter];
```

Specifying an array of arrays of sub emitters will choose a random array and all the sub emitters in the chose array will be attached to the spawned particle.
```javascript
particleSystem.subEmitters = [[subEmitter],[subEmitter, subEmitter2, subEmitter3], [subEmitter4]];
```

## END sub emitter type
When a particle dies one of the particle systems in the array is selected at random as the one to be spawned. It is then cloned and rendered. Any element of the array can itself have `subEmitters` and hence a chain of sub emitters can be formed. In this case the property `manualEmitCount` could be used to avoid an infinite loop of creating and spawning new systems.

## ATTACHED sub emitter type
When a particle is spawned this emitter will be cloned and attached to the new particle. This can be used to create a trailing particle effect on new particles.

To support attached sub emitter's to have their orientation accounted for when emitting particles, their emitter must be a mesh type:
```javascript
subEmitter.particleSystem.emitter = new BABYLON.Mesh("", scene);
```

## Active Sub Systems
Each particle system with that has sub emitters also has a property `activeSubSystems` which is an array containing all currently active sub particle systems.

You can stop the root `ParticleSystem` and all `activeSubSystems` by calling the stop function on the root system:

```javascript
particleSystem.stop(); 
```

When you want to stop the root system without affecting the `activeSubSystems`, you pass false to the Stop function:

```javascript
particleSystem.stop(false);
```

## Demos

<Playground id="#T0L01N#47" title="Sub Emitters" description="Simple example of sub emitters."/>
<Playground id="#9NHBCC#1" title="Sub Emitters On Death Only" description="Simple example of sub emitters on death only"/>
<Playground id="#7HH1UH#6" title="Complete example (hit Space to launch a barrel)" description="Complete Sub Emitter Example"/>


# GPU Particles

Starting from Babylon.js v3.2, you can leverage a new WebGL2 feature, the transform feedback buffer, to drastically boost the performance of particles. Whereas regular particles use the CPU for animation and the GPU for rendering the new WebGL2 API allows Babylon.js to use the GPU for both animation and rendering. With GPU particles, everything is offloaded to the GPU.

Unfortunately this feature is only available when WebGL2 is available. You can use `BABYLON.GPUParticleSystem.IsSupported` to detect if GPU particles can be used. When they are supported, GPU particles can almost be used like regular particles:

```javascript
var particleSystem = new BABYLON.GPUParticleSystem("particles", { capacity:1000000 }, scene);
```

As CPU is no longer involved, you can go crazy with active particles (1000000 in this example). Also, you can use `particleSystem.activeParticleCount` to define the number of active particle count if you want to limit the GPU usage.

**Note:** Sub emitters are not supported in GPU particles.

## Random Texture
It is a shame but there is no good way to get random numbers when running on the GPU. To fill this gap, Babylon.js will create a texture filled with thousands of random values. These values will be read by the particle update shader to animate the particles.
By default the biggest supported texture size is used (16K). You may want to reduce the size of this texture by initializing the system like this:

```javascript
var particleSystem = new BABYLON.GPUParticleSystem("particles", { capacity:1000000, randomTextureSize: 4096 }, scene);
```

## Fallback
As the GPUParticleSystem and the ParticleSystem share almost all their API, it is easy to switch from one to another when WebGL2 is not supported. Keep in mind that the CPU cannot animate as many particles as the GPU can. So you will probably have to reduce the capacity of your system when not using the GPUParticleSystem.

## Stopping a GPU Particle System
When calling `system.stop()` on a `GPUParticleSystem` object, you will force the system to stop generating new particles. But particles will still be rendered even if not visible.

To completely stop a `GPUParticleSystem`, you have to call `dispose()` on it.

## Using custom effects to render the particle system

New since 5.0, you can now use a custom effects with GPU particles!

GPU Particles with custom effect: <Playground id="#1ASENS#68" title="GPU Particles with custom effect" description="Simple example of a GPU particle system using a custom effect for display."/>

## Unsupported Features
The following features are not supported by GPU particles due to their inner nature:
- ManualEmitCount
- disposeOnStop
- Dual values per gradient (only one value is supported)
- Emit rate gradients are not supported
- Start size gradients are not supported
- Mesh emitter

## Example

GPU Particles: <Playground id="#PU4WYI#4" title="GPU Particles Example" description="Simple example of a GPU particle systems."/>



# Color Ramps and Blends, and Billboard Mode

## Ramp Gradients
Ramp gradients produce a gradient color texture by assigning a color to an index between 0 and 1

![ramp gradient](/img/how_to/Particles/rampgrad.png)

To produce a gradient color texture, such as the color bar above, you need the *addRampGradient* method

```javascript
particleSystem.addRampGradient(fraction_of_bar, color3);
```
For this particular color bar you use
```
particleSystem.addRampGradient(0.0, new BABYLON.Color3(1, 1, 1));
particleSystem.addRampGradient(0.09, new BABYLON.Color3(209/255, 204/255, 15/255));
particleSystem.addRampGradient(0.18, new BABYLON.Color3(221/255, 120/255, 14/255));
particleSystem.addRampGradient(0.28, new BABYLON.Color3(200/255, 43/255, 18/255));
particleSystem.addRampGradient(0.47, new BABYLON.Color3(115/255, 22/255, 15/255));
particleSystem.addRampGradient(0.88, new BABYLON.Color3(14/255, 14/255, 14/255));
particleSystem.addRampGradient(1.0, new BABYLON.Color3(14/255, 14/255, 14/255));
```
To use them you need to turn them on.
```javascript
particleSystem.useRampGradients = true;
```

By default the alpha value of the particle (built from `textureAlpha * particleColorAlpha`) is used to as the index get the ramp color from the ramp gradient using this formula: `finalColor = textureColor * particleColor * rampColor`.

Ramp gradient: <Playground id="#0K3AQ2#42" title="Ramp Gradient Example" description="Simple example of using ramp gradients."/>

To give you more control you can use a remap function to change the index over time with  
```javascript
particleSystem.addColorRemapGradient(fraction_of_lifetime_elapsed, minimum_index, maximum_index); //set a range of values for the index at the given time point
```

```javascript
particleSystem.addColorRemapGradient(0, 0, 0.1);
particleSystem.addColorRemapGradient(0.2, 0.1, 0.8);
particleSystem.addColorRemapGradient(0.3, 0.2, 0.85);
particleSystem.addColorRemapGradient(0.35, 0.4, 0.85);
particleSystem.addColorRemapGradient(0.4, 0.5, 0.9);
particleSystem.addColorRemapGradient(0.5, 0.95, 1.0);
particleSystem.addColorRemapGradient(1.0, 0.95, 1.0);
```

The color remap gradients define a min and max that will vary over the particle lifetime.  The index is then remapped from [min, max] to [0, 1] with this formula: `finalIndex = clamp((index - min) / (max - min), 0.0, 1.0)`.

With remap over lifetime of particle: <Playground id="#0K3AQ2#43" title="Ramp Gradient With Remap Over Liftetime" description="Simple example of using ramp gradients with a remap over the lifetime of the particle."/>

Ultimately you can also remap the alpha value generated per pixel with:
```
particleSystem.addAlphaRemapGradient(0, 0, 0.1);
particleSystem.addAlphaRemapGradient(1.0, 0.1, 0.8);
```

The alpha remap will compute the final index value using this formula: `finalIndex = clamp((textureAlpha * particleColorAlpha * rampColor.a - min) / (max - min), 0.0, 1.0)`.


## Particle blending
There are different ways that particles are blended with the scene and these are set with `blendMode`.

```javascript
particleSystem.blendMode = BABYLON.ParticleSystem.BLENDMODE_ONEONE;
```

```javascript
particleSystem.blendMode = BABYLON.ParticleSystem.BLENDMODE_STANDARD;
```

* `BLENDMODE_ONEONE` - colors are added without alpha affecting the result, default;
* `BLENDMODE_STANDARD` - colors are added using particle’s alpha (ie. color * (1 - alpha) + particleColor * alpha).
* `BLENDMODE_ADD` - colors are added but only particle color uses particle’s alpha (ie. color + particleColor * alpha).
* `BLENDMODE_MULTIPLY` - colors are multiplied and added to (1 - alpha) (ie. color * particleColor +  1 - alpha). 
* `BLENDMODE_MULTIPLYADD` - two passes rendering with `BLENDMODE_MULTIPLY` and then `BLENDMODE_ADD`. 

## Billboard Modes
By default all particles are rendered as billboards, that is to face the camera. But you can decide to instead align them with particle direction with 
```javascript
particleSystem.isBillboardBased = false;
```

When billboard is enabled you can decide to either have a full billboard (on all axes) or only on Y axis with this code:

```javascript
particleSystem.billboardMode = BABYLON.ParticleSystem.BILLBOARDMODE_Y;
```

You can also use stretched billboard which will be like a full billboard mode but with an additional rotation to align particles with their direction.

```javascript
particleSystem.billboardMode = BABYLON.ParticleSystem.BILLBOARDMODE_STRETCHED;
```

## Examples
Billboard mode Y - steam: <Playground id="#B9HKG0#10" title="Billboard Mode Y" description="Simple example of using billboard mode in Y."/>
Billboard false - spherical: <Playground id="#EV0SEQ" title="Billboard Mode False" description="Simple example of setting billboard mode to false."/>
Multiply blend mode - smoke pillar: <Playground id="#KUDH9F#1" title="Multiply Blend Mode" description="Simple example of setting particle blend mode to multiply."/>
Add blend mode and billboard mode stretched - sparks (select scene, press space): <Playground id="#5A4TP5" title="Add Blend Mode And Stretched Billboard Mode" description="Simple example of setting particle blend mode to add and billboard mode to stretched."/>
Ramp and blend - explosion (select scene, press space): <Playground id="#VS5XS7#8" title="Ramp and Blend" description="Simple example of a ramp and blend."/>

Sub Emitters

How To Use Sub Emitters

END sub emitter type

ATTACHED sub emitter type

Active Sub Systems

Demos

Further reading

Particle System

Learn all about the particle system in Babylon.js.

Particles

Dive into the rich and exciting world of particles in Babylon.js.

Animating Particles

Learn how to animate particles in Babylon.js.

Solid Particle System

Learn all about the solid particle system in Babylon.js.

Customizing Particles

Learn how to customize particles in Babylon.js.