Particles now emit at a specified rate and correctly obey parent positions

examples/particles/particles.js

@@ -4,6 +4,7 @@ import MomentumEngine from "../../src/es6";
 
 let white = new MomentumEngine.Classes.Color(255, 255, 255);
 
+
 class BlueParticle extends MomentumEngine.Classes.Rect {
 
     constructor (x, y) {
@@ -15,11 +16,11 @@ class BlueParticle extends MomentumEngine.Classes.Rect {
 
 window.onload = function () {
 
-    var width = 640,
+    let width = 640,
         height = 360,
         baseSize = width / 64;
 
-    var particles = new MomentumEngine.Classes.Game({
+    let particles = new MomentumEngine.Classes.Game({
         canvas: document.getElementById("canvas"),
         width: width,
         height: height,
@@ -27,19 +28,23 @@ window.onload = function () {
         desiredFps: 60
     });
 
-    var black = new MomentumEngine.Classes.Color(0, 0, 0),
+    let black = new MomentumEngine.Classes.Color(0, 0, 0),
         red = new MomentumEngine.Classes.Color(255, 0, 0);
 
-    var mainScene = new MomentumEngine.Classes.Rect(0, 0, width, height, black);
+    let mainScene = new MomentumEngine.Classes.Rect(0, 0, width, height, black);
     particles.addChildEntity(mainScene);
 
-    var rect = new MomentumEngine.Classes.Rect(width / 2 - baseSize, height / 2 - baseSize, baseSize * 2, baseSize * 2, red),
-        emitter = new MomentumEngine.Classes.Emitter(0, 0, new MomentumEngine.Classes.Vector2D(1, 1), BlueParticle);
+    let rect = new MomentumEngine.Classes.Rect(width / 10 - baseSize, height - (baseSize * 10), baseSize * 2, baseSize * 2, red),
+        emitter = new MomentumEngine.Classes.Emitter(baseSize, baseSize, 2, new MomentumEngine.Classes.Vector2D(1, 1), BlueParticle);
 
     mainScene.addChildEntity(rect);
     rect.addChildEntity(emitter);
+    rect.setVelocity(0.01, 0);
+    rect.setAcceleration(0.01, 0);
 
+    emitter.setParticleParent(mainScene);
     emitter.emitting = true;
+
     particles.start();
 
 };

src/classes/emitter.js

@@ -7,46 +7,88 @@ import Vector2D from "./vector2d.js";
 class Emitter extends Entity {
 
 
-    constructor (x, y, velocity, particle) {
+    constructor (x, y, rate, velocity, particle) {
 
         super(x, y);
 
         this.particleVelocity = velocity;
         this.particleClass = particle;
+
+        this.emitRate = rate;
         this.emitting = false;
+        this._lastEmitTime = this._creationTime;
+        this._wasEmitting = false;
 
         this.particles = [];
 
         this.spread = function () {
-            return Math.PI / 32;
+            return Math.PI / 1;
         }
 
     }
 
 
+    setParticleParent (entity) {
+        this._particleParent = entity;
+    }
+
+
     _emit () {
 
+        let ParticleClass = this.particleClass,
+            parent = this._particleParent || this._parent;
+
+        let angle = this.particleVelocity.angle() + this.spread() - (Math.random() * this.spread() * 2),
+            magnitude = this.particleVelocity.length(),
+            velocity = Vector2D.fromAngle(angle, magnitude);
+
+        let particle = new ParticleClass(this._calculatedPos.x, this._calculatedPos.y);
+        particle.velocity = velocity;
+
+        this.particles.push(particle);
+        parent.addChildEntity(particle);
+
+    }
+
+
+    _triggerEmissions () {
+
+        // We prematurely call preprocess so that child particles can spawn from the emitters permission but be children of a different parent
+        // NK: This might cause a bug where child renders have an incorrect position because preprocess should normally be called after the update function but before the render, here it is before update. We'll see.
+        this._preprocess();
+
         if (this.emitting) {
 
-            let ParticleClass = this.particleClass;
+            let currentTime = +(new Date());
 
-            let angle = this.particleVelocity.angle() + this.spread() - (Math.random() * this.spread() * 2),
-                magnitude = this.particleVelocity.length(),
-                velocity = Vector2D.fromAngle(angle, magnitude);
+            if (!this._wasEmitting) {
+                this._wasEmitting = true;
+                this._lastEmitTime = currentTime;
+            }
 
-            let particle = new ParticleClass(this.pos.x, this.pos.y);
-            particle.velocity = velocity;
+            // In honour the code of Alex Evans
+            let emitDelta = currentTime - this._lastEmitTime;
+            if (emitDelta > this.emitRate) {
 
-            this.particles.push(particle);
-            this._parent.addChildEntity(particle);
+                let emissions = ~~(emitDelta / this.emitRate);
 
+                this._lastEmitTime = currentTime + (emitDelta - (this.emitRate * emissions));
+
+                for (let i = 0; i < emissions; i++) {
+                    this._emit();
+                }
+
+            }
+
+        } else {
+            this._wasEmitting = false;
         }
 
     }
 
 
     update () {
-        this._emit();
+        this._triggerEmissions();
     }
 
 

src/classes/entity.js

@@ -19,6 +19,8 @@ class Entity {
         this._game = null;
         this._parent = null;
 
+        this._creationTime = +(new Date());
+
     }
 
 
@@ -130,6 +132,12 @@ class Entity {
 
     _updateEntity (delta) {
 
+        if (this.timeToLive) {
+            if (+(new Date()) - this._creationTime > this.timeToLive) {
+                this._parent.detachChildEntity(this);
+            }
+        }
+
         // Calculate new position based on velocity and acceleration if there's one set
         if (this.velocity) {