var system = new Partykals.ParticlesSystem({
        container: scene, // <-- THREE.JS object to attach system to.
        particles: {
            // particles options, will be described later..
        },
        system: {
            // system options, will be described later..
            emitters: // emitter(s), will be described later
        }
    });

system.update();

// scene and renderer are assumed to be created here..

// create  particles system:
var system = new Partykals.ParticlesSystem({
    container: scene,
    particles: {
        globalSize: 5,
        ttl: 10,
        velocity: new Partykals.Randomizers.SphereRandomizer(12.5),
        velocityBonus: new THREE.Vector3(0, 25, 0),
        gravity: -10,
        startColor: new Partykals.Randomizers.ColorsRandomizer(),
        endColor: new Partykals.Randomizers.ColorsRandomizer(),
    },
    system: {
        particlesCount: 1000,
        emitters: new Partykals.Emitter({
            onInterval: new Partykals.Randomizers.MinMaxRandomizer(0, 5),
            interval: new Partykals.Randomizers.MinMaxRandomizer(0, 0.25),
        }),
        speed: 1,
    }
});

// update loop
function animate() {

    requestAnimationFrame( animate );
    system.update();
    renderer.render( scene, camera );

}

/*
* // PARTICLES OPTIONS
* ============================================================================
* @param {*} options.particles Particle-related options.
* 
* // PARTICLES TTL
* @param {Number} options.particles.ttl How long, in seconds, every particle lives.
* @param {Number} options.particles.ttlExtra If provided, will add random numbers from 0 to ttlExtra to particle's ttl.
* 
* // PARTICLES FADING / ALPHA
* @param {Boolean} options.particles.alpha Per-particle constant alpha; either a constant value (Number) or a Partykals.Randomizers.Randomizer instance to create random values.
* @param {Number} options.particles.startAlpha Particles starting opacity; either a constant value (Number) or a Partykals.Randomizers.Randomizer instance to create random values.
* @param {Number} options.particles.endAlpha Particles ending opacity; either a constant value (Number) or a Partykals.Randomizers.Randomizer instance to create random values.
* @param {Number} options.particles.startAlphaChangeAt Will only start shifting alpha when age is over this value; either a constant value (Number) or a Partykals.Randomizers.Randomizer instance to create random values.
* 
* // PARTICLES GROWING / SIZE
* @param {Number} options.particles.size Per-particle constant size; either a constant value (Number) or a Partykals.Randomizers.Randomizer instance to create random values.
* @param {Number} options.particles.startSize Particles starting size; either a constant value (Number) or a Partykals.Randomizers.Randomizer instance to create random values.
* @param {Number} options.particles.endSize Particles ending size; either a constant value (Number) or a Partykals.Randomizers.Randomizer instance to create random values.
* @param {Number} options.particles.startSizeChangeAt Will only start shifting size when age is over this value; either a constant value (Number) or a Partykals.Randomizers.Randomizer instance to create random values.
* 
* // PARTICLES COLORING
* @param {THREE.Color} options.particles.color Per-particle constant color; either a constant value (THREE.Color) or a Partykals.Randomizers.Randomizer instance to create random values.
* @param {THREE.Color} options.particles.startColor Starting color min value; either a constant value (THREE.Color) or a Partykals.Randomizers.Randomizer instance to create random values.
* @param {THREE.Color} options.particles.endColor Ending color min value; either a constant value (THREE.Color) or a Partykals.Randomizers.Randomizer instance to create random values.
* @param {Number} options.particles.startColorChangeAt Will only start shifting color when age is over this value; either a constant value (Number) or a Partykals.Randomizers.Randomizer instance to create random values.
* 
* // PARTICLES ACCELERATION 
* @param {THREE.Vector3} options.particles.acceleration Particles acceleration; either a constant value (THREE.Vector3) or a Partykals.Randomizers.Randomizer instance to create random values.
* @param {Number} options.particles.gravity Gravity force affecting the particles.    
* 
* // PARTICLES ROTATION
* @param {Number} options.particles.rotation Per-particle rotation (only works with texture); either a constant value (Number) or a Partykals.Randomizers.Randomizer instance to create random values.
* @param {Number} options.particles.rotationSpeed Particles rotation speed (only works with texture); either a constant value (Number) or a Partykals.Randomizers.Randomizer instance to create random values.
* 
* // PARTICLES VELOCITY 
* @param {*} options.particles.velocity Particles starting velocity; either a constant value (THREE.Vector3) or a Partykals.Randomizers.Randomizer instance to create random values.
* @param {THREE.Vector3} options.particles.velocityBonus Velocity value to add to all particles after randomizing velocity.
* 
* // PARTICLES OFFSET
* @param {THREE.Vector3} options.particles.offset Particles offset from system's center; either a constant value (THREE.Vector3) or a Partykals.Randomizers.Randomizer instance to create random values.
* 
* // PARTICLE GLOBALS
* @param {Boolean} options.particles.worldPosition If true, particles will maintain their world position after spawn even if the system moves.
* @param {Number} options.particles.globalSize Const size for all particles. Note: this is more efficient than setting per-particle size property.
* @param {Number} options.particles.globalColor Global color to affect all particles. Note: this is more efficient than setting per-particle color property.
* @param {String} options.particles.blending Particles blending mode (opaque / blend / additive).
* @param {THREE.Texture} options.particles.texture Particle's texture to use.
* 
* // CUSTOM CALLBACKS
* @param {Function} options.particles.onUpdate Optional method to call per-particle every update frame.
* @param {Function} options.particles.onSpawn Optional method to call per-particle every time a particle spawns (after everything is set).
*  */

/*
* // SYSTEM OPTIONS
* ============================================================================
* @param {*} options.system System-related options.
* @param {Number} options.system.particlesCount Particles count.
* @param {Number} options.system.ttl How long, in seconds, the particle system lives.
* @param {Number} options.system.speed Speed factor to affect all particles and emitting. Note: the only thing this don't affect is system's ttl.
* @param {Function} options.system.onUpdate Optional method to call every update frame.
* @param {Partykals.Emitter} options.system.emitters A single emitter or a list of emitters to attach to this system.
* @param {Boolean} options.system.perspective If true, will scale particles based on distance from camera.
* @param {Number} options.system.scale Overall system scale when in perspective mode (if perspective=false, will be ignored). A good value is between 400 and 600.
* @param {Boolean} options.system.depthWrite Should we perform depth write? (default to true).
* @param {Boolean} options.system.depthTest Should we perform depth test? (default to true).
*/

var emitter = new Partykals.Emitter(options);

/*
* @param {*} options Emitter options.
* @param {*} options.onSpawnBurst Burst of particles when particle system starts; either a constant value (Number) or a Partykals.Randomizers.Randomizer instance to create random numbers.
* @param {*} options.onInterval Burst of particles every interval; either a constant value (Number) or a Partykals.Randomizers.Randomizer instance to create random numbers.
* @param {Number} options.interval Spawn interval time, in seconds; either a constant value (Number) or a Partykals.Randomizers.Randomizer instance to create random numbers.
* @param {Number} options.detoretingMinTtl If provided and particle system's ttl is below this value, will start emitting less and less until stopping completely.
*/