# A particles generator in rust for laser shows


## Philosophy 

This library should allow users to define their own particle behaviours

- how many particles at start? min/max at any time? how many to add at any time?
- how do particles behave? Are there different types? Different shapes?
- how do particles react with real world? To audio? To a controller?

## Constraints

- Render as lists of points in the form [x,y,color] with color encoded as 12 bits (r,g,b)
    - i.e. it doesn't speak to the laser directly, we use a middleware for that part (see. xxx)
    - it can output to STDOUT or send to redis
- Obviously be as fast as possible
- Use a physics engine as a tool for collision detection, velocity and more
- Be easy to use: good defaults for everything
- Handle bounding and drawing boxes
- Handle user custom particle properties (ex: decay, frequency, personality, etc.)
- Handle additional drawings for the current frame due to custom events (ex: random edge between two particles)

## Questions 

### Working with the Physics engine 

    - Q: how do we enable custom behaviours (ex: reacting to audio)
    - Q: how do we map physics engine object (ex: ball, square) for users as concept
    - Q: how do we convert the physics engine objets to 2D points
    - Q: how do we handle 3D? On by default? 

## How to use in a project

1. Clone lj_rust_template and edit draw.rs
2. add lj_particle library crate
3. edit the draw function 
4. compile

## Fundamental Features
- [ ] Use a 3D physics engine
- [ ] Provide hooks to create and update the simulation (onInit, onTick, onCollide, etc.)
- [ ] Render using box clipping for out of bound particles points
- [ ] Use an out-of-simulation list of additional points
- [ ] Render to STDOUT or Redis 

## Future Features 

- [ ] Use a 2D physics engine
- [ ] Use attractors/repulsors objects
- [ ] Use OSC to update configuration

## Library struct/objects

```
Particle
- PhysicsBody
- Shape : Square, Triangle, Circle, 3DSphere 
- UserData // custom ex: life decay, seed, created_at, frequency
- Group 

PhysicsEngine
PhysicsEngineConfig

RenderEngine
RenderEngineConfig


Config
- ParticlesGroups: vec<<Particle>
- RedisConfig
- PhysicsEngineConfig
- RenderEngineConfig

// future feature
OSCConfig
- OSCCache
- OSCServer <IP,Port>
````

## API example

```rust

/***
  An idea of the crate API
***/

use LJParticleSystem as ParticleSystem;
use LJRedilysis as Redilysis;
use Rapier as PhysicsEngine;

// Configure 
let boundingbox  = BoundingBox();
let clipping_box = ClippingBox();

let particle_system = ParticleSystem( ParticleSystemConfig, PhysicsEngine, ClippingBox, BoundingBox );
let redilysis  = Redilysis ( RedilysisConfig( file_path ) );


// by default, equiprobability to generate a particle from any group
particle_system.new_particle( lambda() => { ... }) 

// some way to init the particles 
world.init();

particle_system.tick = lambda(){

    // Configuration update if read via OSC 
    current_config = self->getConfig();

    // Retrieve bandwidth/bpm/rms info (with caching)
    analysis = redilysis.update();

    // Manage 
    self.boundingBox();

    self.physicsEngine();

    for( particle in self.getParticles() ) {

         


    }


    n_particles = current_config.particles_amount;

    return self.clippingBox();


}

pub fn draw() -> Result<Vec<Point>, Box<dyn std::error::Error>> {
    let mut v: Vec<Point> = vec![];
    v.push( particle_system.tick() );
    Ok(v)
}

```


## OSC CONFIG

### Actors and notations

```
- [S] Server / (LJ) OSC Server and client
eventual config
 channel 1 : IP
 channel X : IP

- [R] Rust = (LJ Particle) OSC Server and Client

- [U] User Interface = (Tablet) HTML Interface

- [c] Program Channel = configurable, uint ex: 1
- [n] Programe name = configurable, string ex: particle_foo_square

``` 

### Sequence Diagram

```
# Prerequisite : [S] is running and available and U is connected to [S]
# [R] starts
# [R]: Do you have my config already ?
[R] -> [S] "/program/${c}/${n}/configure" 

# [S] needs to stock which program is currently used for ${n} channel and its parameters

# If no, [S] manifests the need to init the configuration
[S] -> [R] "/program/${c}/${n}/no-config"

# If no-config, [R] sends its default config for [S] to store
[R] -> [S] "/program/${c}/${n}/var1 default_value1" # etc.

# In any case, [S] sends to [R] the current config
[S] -> [R] "/program/${c}/${n}/var1 value1" # etc.

# [S] creates an event for the User to change  
[S] -> U "/program/${c}/${n}" 

# U can change the program configuration 
U -> [S] "/program/${c}/${n}" 

```