module BABYLON {

    /**
     * This represents a particle system in Babylon.
     * Particles are often small sprites used to simulate hard-to-reproduce phenomena like fire, smoke, water, or abstract visual effects like magic glitter and faery dust.
     * Particles can take different shapes while emitted like box, sphere, cone or you can write your custom function.
     * @example https://doc.babylonjs.com/babylon101/particles
     */
    export class ParticleSystem extends BaseParticleSystem implements IDisposable, IAnimatable, IParticleSystem {
        /**
         * This function can be defined to provide custom update for active particles.
         * This function will be called instead of regular update (age, position, color, etc.).
         * Do not forget that this function will be called on every frame so try to keep it simple and fast :)
         */
        public updateFunction: (particles: Particle[]) => void;      

        private _emitterWorldMatrix: Matrix;

        /**
         * This function can be defined to specify initial direction for every new particle.
         * It by default use the emitterType defined function
         */
        public startDirectionFunction: (worldMatrix: Matrix, directionToUpdate: Vector3, particle: Particle) => void;
        /**
         * This function can be defined to specify initial position for every new particle.
         * It by default use the emitterType defined function
         */
        public startPositionFunction: (worldMatrix: Matrix, positionToUpdate: Vector3, particle: Particle) => void;

        /**
        * An event triggered when the system is disposed
        */
        public onDisposeObservable = new Observable<ParticleSystem>();

        private _onDisposeObserver: Nullable<Observer<ParticleSystem>>;
        /**
         * Sets a callback that will be triggered when the system is disposed
         */
        public set onDispose(callback: () => void) {
            if (this._onDisposeObserver) {
                this.onDisposeObservable.remove(this._onDisposeObserver);
            }
            this._onDisposeObserver = this.onDisposeObservable.add(callback);
        }

        private _particles = new Array<Particle>();
        private _epsilon: number;
        private _capacity: number;
        private _stockParticles = new Array<Particle>();
        private _newPartsExcess = 0;
        private _vertexData: Float32Array;
        private _vertexBuffer: Nullable<Buffer>;
        private _vertexBuffers: { [key: string]: VertexBuffer } = {};
        private _spriteBuffer: Nullable<Buffer>;
        private _indexBuffer: Nullable<WebGLBuffer>;
        private _effect: Effect;
        private _customEffect: Nullable<Effect>;
        private _cachedDefines: string;
        private _scaledColorStep = new Color4(0, 0, 0, 0);
        private _colorDiff = new Color4(0, 0, 0, 0);
        private _scaledDirection = Vector3.Zero();
        private _scaledGravity = Vector3.Zero();
        private _currentRenderId = -1;
        private _alive: boolean;
        private _useInstancing = false;

        private _started = false;
        private _stopped = false;
        private _actualFrame = 0;
        private _scaledUpdateSpeed: number;
        private _vertexBufferSize: number;

        /** @hidden */
        public _currentEmitRateGradient: Nullable<FactorGradient>;
        /** @hidden */
        public _currentEmitRate1 = 0;
        /** @hidden */
        public _currentEmitRate2 = 0;   
        
        /** @hidden */
        public _currentStartSizeGradient: Nullable<FactorGradient>;
        /** @hidden */
        public _currentStartSize1 = 0;
        /** @hidden */
        public _currentStartSize2 = 0;   

        // end of sheet animation

        // Sub-emitters
        /**
         * this is the Sub-emitters templates that will be used to generate particle system when the particle dies, this property is used by the root particle system only.
         */
        public subEmitters: ParticleSystem[];
        /**
        * The current active Sub-systems, this property is used by the root particle system only.
        */
        public activeSubSystems: Array<ParticleSystem>;
        
        private _rootParticleSystem: ParticleSystem;
        //end of Sub-emitter

        /**
         * Gets the current list of active particles
         */
        public get particles(): Particle[] {
            return this._particles;
        }

        /**
         * Returns the string "ParticleSystem"
         * @returns a string containing the class name
         */
        public getClassName(): string {
            return "ParticleSystem";
        }

        /**
         * Instantiates a particle system.
         * Particles are often small sprites used to simulate hard-to-reproduce phenomena like fire, smoke, water, or abstract visual effects like magic glitter and faery dust.
         * @param name The name of the particle system
         * @param capacity The max number of particles alive at the same time
         * @param scene The scene the particle system belongs to
         * @param customEffect a custom effect used to change the way particles are rendered by default
         * @param isAnimationSheetEnabled Must be true if using a spritesheet to animate the particles texture
         * @param epsilon Offset used to render the particles
         */
        constructor(name: string, capacity: number, scene: Scene, customEffect: Nullable<Effect> = null, isAnimationSheetEnabled: boolean = false, epsilon: number = 0.01) {
            super(name);

            this._capacity = capacity;

            this._epsilon = epsilon;
            this._isAnimationSheetEnabled = isAnimationSheetEnabled;

            this._scene = scene || Engine.LastCreatedScene;

            // Setup the default processing configuration to the scene.
            this._attachImageProcessingConfiguration(null);

            this._customEffect = customEffect;

            this._scene.particleSystems.push(this);

            this._useInstancing = this._scene.getEngine().getCaps().instancedArrays;

            this._createIndexBuffer();
            this._createVertexBuffers();

            // Default emitter type
            this.particleEmitterType = new BoxParticleEmitter();

            this.updateFunction = (particles: Particle[]): void => {
                let noiseTextureData: Nullable<Uint8Array> = null;
                let noiseTextureSize: Nullable<ISize> = null;

                if (this.noiseTexture) { // We need to get texture data back to CPU
                    noiseTextureData = <Nullable<Uint8Array>>(this.noiseTexture.readPixels());
                    noiseTextureSize = this.noiseTexture.getSize();
                }

                for (var index = 0; index < particles.length; index++) {
                    var particle = particles[index];
                    particle.age += this._scaledUpdateSpeed;

                    if (particle.age >= particle.lifeTime) { // Recycle by swapping with last particle
                        this._emitFromParticle(particle);
                        this.recycleParticle(particle);
                        index--;
                        continue;
                    }
                    else {
                        let ratio = particle.age / particle.lifeTime;

                        // Color
                        if (this._colorGradients && this._colorGradients.length > 0) {
                            Tools.GetCurrentGradient(ratio, this._colorGradients, (currentGradient, nextGradient, scale) => {
                                if (currentGradient !== particle._currentColorGradient) {
                                    particle._currentColor1.copyFrom(particle._currentColor2);
                                    (<ColorGradient>nextGradient).getColorToRef(particle._currentColor2);    
                                    particle._currentColorGradient = (<ColorGradient>currentGradient);
                                }
                                Color4.LerpToRef(particle._currentColor1, particle._currentColor2, scale, particle.color);
                            });
                        }
                        else {
                            particle.colorStep.scaleToRef(this._scaledUpdateSpeed, this._scaledColorStep);
                            particle.color.addInPlace(this._scaledColorStep);

                            if (particle.color.a < 0) {
                                particle.color.a = 0;
                            }
                        }

                        // Angular speed
                        if (this._angularSpeedGradients && this._angularSpeedGradients.length > 0) {                  
                            Tools.GetCurrentGradient(ratio, this._angularSpeedGradients, (currentGradient, nextGradient, scale) => {
                                if (currentGradient !== particle._currentAngularSpeedGradient) {
                                    particle._currentAngularSpeed1 = particle._currentAngularSpeed2;
                                    particle._currentAngularSpeed2 = (<FactorGradient>nextGradient).getFactor();    
                                    particle._currentAngularSpeedGradient = (<FactorGradient>currentGradient);
                                }                                
                                particle.angularSpeed = Scalar.Lerp(particle._currentAngularSpeed1, particle._currentAngularSpeed2, scale);
                            });
                        }                        
                        particle.angle += particle.angularSpeed * this._scaledUpdateSpeed;

                        // Direction
                        let directionScale = this._scaledUpdateSpeed;

                        /// Velocity
                        if (this._velocityGradients && this._velocityGradients.length > 0) {                  
                            Tools.GetCurrentGradient(ratio, this._velocityGradients, (currentGradient, nextGradient, scale) => {
                                if (currentGradient !== particle._currentVelocityGradient) {
                                    particle._currentVelocity1 = particle._currentVelocity2;
                                    particle._currentVelocity2 = (<FactorGradient>nextGradient).getFactor();    
                                    particle._currentVelocityGradient = (<FactorGradient>currentGradient);
                                }                                
                                directionScale *= Scalar.Lerp(particle._currentVelocity1, particle._currentVelocity2, scale);
                            });
                        }                  
                        
                        particle.direction.scaleToRef(directionScale, this._scaledDirection);

                        /// Limit velocity
                        if (this._limitVelocityGradients && this._limitVelocityGradients.length > 0) {                  
                            Tools.GetCurrentGradient(ratio, this._limitVelocityGradients, (currentGradient, nextGradient, scale) => {
                                if (currentGradient !== particle._currentLimitVelocityGradient) {
                                    particle._currentLimitVelocity1 = particle._currentLimitVelocity2;
                                    particle._currentLimitVelocity2 = (<FactorGradient>nextGradient).getFactor();    
                                    particle._currentLimitVelocityGradient = (<FactorGradient>currentGradient);
                                }                                
                                
                                let limitVelocity = Scalar.Lerp(particle._currentLimitVelocity1, particle._currentLimitVelocity2, scale);
                                let currentVelocity = particle.direction.length();

                                if (currentVelocity > limitVelocity) {
                                    particle.direction.scaleInPlace(this.limitVelocityDamping);
                                }
                            });
                        }   

                        /// Drag
                        if (this._dragGradients && this._dragGradients.length > 0) {                  
                            Tools.GetCurrentGradient(ratio, this._dragGradients, (currentGradient, nextGradient, scale) => {
                                if (currentGradient !== particle._currentDragGradient) {
                                    particle._currentDrag1 = particle._currentDrag2;
                                    particle._currentDrag2 = (<FactorGradient>nextGradient).getFactor();    
                                    particle._currentDragGradient = (<FactorGradient>currentGradient);
                                }                                
                                
                                let drag = Scalar.Lerp(particle._currentDrag1, particle._currentDrag2, scale);

                                this._scaledDirection.scaleInPlace(1.0 - drag);
                            });
                        }                           

                        particle.position.addInPlace(this._scaledDirection);

                        // Noise
                        if (noiseTextureData && noiseTextureSize) {
                            let localPosition = Tmp.Vector3[0];
                            let emitterPosition = Tmp.Vector3[1];

                            this._emitterWorldMatrix.getTranslationToRef(emitterPosition);
                            particle.position.subtractToRef(emitterPosition, localPosition);

                            let fetchedColorR = this._fetchR(localPosition.y, localPosition.z, noiseTextureSize.width, noiseTextureSize.height, noiseTextureData);
                            let fetchedColorG = this._fetchR(localPosition.x + 0.33, localPosition.z + 0.33, noiseTextureSize.width, noiseTextureSize.height, noiseTextureData);
                            let fetchedColorB = this._fetchR(localPosition.x - 0.33, localPosition.y - 0.33, noiseTextureSize.width, noiseTextureSize.height, noiseTextureData);
                            
                            let force = Tmp.Vector3[0];
                            let scaledForce = Tmp.Vector3[1];

                            force.copyFromFloats((2 * fetchedColorR - 1) * this.noiseStrength.x, (2 * fetchedColorG - 1) * this.noiseStrength.y, (2 * fetchedColorB - 1) * this.noiseStrength.z);

                            force.scaleToRef(this._scaledUpdateSpeed, scaledForce);
                            particle.direction.addInPlace(scaledForce);
                        }

                        // Gravity
                        this.gravity.scaleToRef(this._scaledUpdateSpeed, this._scaledGravity);
                        particle.direction.addInPlace(this._scaledGravity);                       

                        // Size
                        if (this._sizeGradients && this._sizeGradients.length > 0) {                  
                            Tools.GetCurrentGradient(ratio, this._sizeGradients, (currentGradient, nextGradient, scale) => {
                                if (currentGradient !== particle._currentSizeGradient) {
                                    particle._currentSize1 = particle._currentSize2;
                                    particle._currentSize2 = (<FactorGradient>nextGradient).getFactor();    
                                    particle._currentSizeGradient = (<FactorGradient>currentGradient);
                                }                                
                                particle.size = Scalar.Lerp(particle._currentSize1, particle._currentSize2, scale);
                            });
                        }

                        if (this._isAnimationSheetEnabled) {
                            particle.updateCellIndex();
                        }
                    }
                }
            }
        }


        private _addFactorGradient(factorGradients: FactorGradient[], gradient: number, factor: number, factor2?: number) {
            let newGradient = new FactorGradient();
            newGradient.gradient = gradient;
            newGradient.factor1 = factor;
            newGradient.factor2 = factor2;
            factorGradients.push(newGradient);

            factorGradients.sort((a, b) => {
                if (a.gradient < b.gradient) {
                    return -1;
                } else if (a.gradient > b.gradient) {
                    return 1;
                }

                return 0;
            });            
        }

        private _removeFactorGradient(factorGradients: Nullable<FactorGradient[]>, gradient: number) {
            if (!factorGradients) {
                return;
            }

            let index = 0;
            for (var factorGradient of factorGradients) {
                if (factorGradient.gradient === gradient) {
                    factorGradients.splice(index, 1);
                    break;
                }
                index++;
            }
        }

        /**
         * Adds a new life time gradient
         * @param gradient defines the gradient to use (between 0 and 1)
         * @param factor defines the life time factor to affect to the specified gradient         
         * @param factor2 defines an additional factor used to define a range ([factor, factor2]) with main value to pick the final value from
         * @returns the current particle system
         */
        public addLifeTimeGradient(gradient: number, factor: number, factor2?: number): IParticleSystem {
            if (!this._lifeTimeGradients) {
                this._lifeTimeGradients = [];
            }

            this._addFactorGradient(this._lifeTimeGradients, gradient, factor, factor2);

            return this;
        }

        /**
         * Remove a specific life time gradient
         * @param gradient defines the gradient to remove
         * @returns the current particle system
         */
        public removeLifeTimeGradient(gradient: number): IParticleSystem {
            this._removeFactorGradient(this._lifeTimeGradients, gradient);

            return this;
        }       

        /**
         * Adds a new size gradient
         * @param gradient defines the gradient to use (between 0 and 1)
         * @param factor defines the size factor to affect to the specified gradient         
         * @param factor2 defines an additional factor used to define a range ([factor, factor2]) with main value to pick the final value from
         * @returns the current particle system
         */
        public addSizeGradient(gradient: number, factor: number, factor2?: number): IParticleSystem {
            if (!this._sizeGradients) {
                this._sizeGradients = [];
            }

            this._addFactorGradient(this._sizeGradients, gradient, factor, factor2);

            return this;
        }

        /**
         * Remove a specific size gradient
         * @param gradient defines the gradient to remove
         * @returns the current particle system
         */
        public removeSizeGradient(gradient: number): IParticleSystem {
            this._removeFactorGradient(this._sizeGradients, gradient);

            return this;
        }        

        /**
         * Adds a new angular speed gradient
         * @param gradient defines the gradient to use (between 0 and 1)
         * @param factor defines the angular speed  to affect to the specified gradient         
         * @param factor2 defines an additional factor used to define a range ([factor, factor2]) with main value to pick the final value from
         * @returns the current particle system
         */
        public addAngularSpeedGradient(gradient: number, factor: number, factor2?: number): IParticleSystem {
            if (!this._angularSpeedGradients) {
                this._angularSpeedGradients = [];
            }

            this._addFactorGradient(this._angularSpeedGradients, gradient, factor, factor2);

            return this;
        }

        /**
         * Remove a specific angular speed gradient
         * @param gradient defines the gradient to remove
         * @returns the current particle system
         */
        public removeAngularSpeedGradient(gradient: number): IParticleSystem {
            this._removeFactorGradient(this._angularSpeedGradients, gradient);

            return this;
        }     
                   
        /**
         * Adds a new velocity gradient
         * @param gradient defines the gradient to use (between 0 and 1)
         * @param factor defines the velocity to affect to the specified gradient         
         * @param factor2 defines an additional factor used to define a range ([factor, factor2]) with main value to pick the final value from
         * @returns the current particle system
         */
        public addVelocityGradient(gradient: number, factor: number, factor2?: number): IParticleSystem {
            if (!this._velocityGradients) {
                this._velocityGradients = [];
            }

            this._addFactorGradient(this._velocityGradients, gradient, factor, factor2);

            return this;
        }

        /**
         * Remove a specific velocity gradient
         * @param gradient defines the gradient to remove
         * @returns the current particle system
         */
        public removeVelocityGradient(gradient: number): IParticleSystem {
            this._removeFactorGradient(this._velocityGradients, gradient);

            return this;
        }     
        
        /**
         * Adds a new limit velocity gradient
         * @param gradient defines the gradient to use (between 0 and 1)
         * @param factor defines the limit velocity value to affect to the specified gradient         
         * @param factor2 defines an additional factor used to define a range ([factor, factor2]) with main value to pick the final value from
         * @returns the current particle system
         */
        public addLimitVelocityGradient(gradient: number, factor: number, factor2?: number): IParticleSystem {
            if (!this._limitVelocityGradients) {
                this._limitVelocityGradients = [];
            }

            this._addFactorGradient(this._limitVelocityGradients, gradient, factor, factor2);

            return this;
        }

        /**
         * Remove a specific limit velocity gradient
         * @param gradient defines the gradient to remove
         * @returns the current particle system
         */
        public removeLimitVelocityGradient(gradient: number): IParticleSystem {
            this._removeFactorGradient(this._limitVelocityGradients, gradient);

            return this;
        }       
        
        /**
         * Adds a new drag gradient
         * @param gradient defines the gradient to use (between 0 and 1)
         * @param factor defines the drag value to affect to the specified gradient         
         * @param factor2 defines an additional factor used to define a range ([factor, factor2]) with main value to pick the final value from
         * @returns the current particle system
         */
        public addDragGradient(gradient: number, factor: number, factor2?: number): IParticleSystem {
            if (!this._dragGradients) {
                this._dragGradients = [];
            }

            this._addFactorGradient(this._dragGradients, gradient, factor, factor2);

            return this;
        }

        /**
         * Remove a specific drag gradient
         * @param gradient defines the gradient to remove
         * @returns the current particle system
         */
        public removeDragGradient(gradient: number): IParticleSystem {
            this._removeFactorGradient(this._dragGradients, gradient);

            return this;
        }         
        
        /**
         * Adds a new emit rate gradient (please note that this will only work if you set the targetStopDuration property)
         * @param gradient defines the gradient to use (between 0 and 1)
         * @param factor defines the emit rate value to affect to the specified gradient         
         * @param factor2 defines an additional factor used to define a range ([factor, factor2]) with main value to pick the final value from
         * @returns the current particle system
         */
        public addEmitRateGradient(gradient: number, factor: number, factor2?: number): IParticleSystem {
            if (!this._emitRateGradients) {
                this._emitRateGradients = [];
            }

            this._addFactorGradient(this._emitRateGradients, gradient, factor, factor2);

            if (!this._currentEmitRateGradient) {
                this._currentEmitRateGradient = this._emitRateGradients[0];
                this._currentEmitRate1 = this._currentEmitRateGradient.getFactor();
                this._currentEmitRate2 = this._currentEmitRate1;
            }

            if (this._emitRateGradients.length === 2) {
                this._currentEmitRate2 = this._emitRateGradients[1].getFactor();
            }

            return this;
        }

        /**
         * Remove a specific emit rate gradient
         * @param gradient defines the gradient to remove
         * @returns the current particle system
         */
        public removeEmitRateGradient(gradient: number): IParticleSystem {
            this._removeFactorGradient(this._emitRateGradients, gradient);

            return this;
        }    
        
        /**
         * Adds a new start size gradient (please note that this will only work if you set the targetStopDuration property)
         * @param gradient defines the gradient to use (between 0 and 1)
         * @param factor defines the start size value to affect to the specified gradient         
         * @param factor2 defines an additional factor used to define a range ([factor, factor2]) with main value to pick the final value from
         * @returns the current particle system
         */
        public addStartSizeGradient(gradient: number, factor: number, factor2?: number): IParticleSystem {
            if (!this._startSizeGradients) {
                this._startSizeGradients = [];
            }

            this._addFactorGradient(this._startSizeGradients, gradient, factor, factor2);

            if (!this._currentStartSizeGradient) {
                this._currentStartSizeGradient = this._startSizeGradients[0];
                this._currentStartSize1 = this._currentStartSizeGradient.getFactor();
                this._currentStartSize2 = this._currentStartSize1;
            }

            if (this._startSizeGradients.length === 2) {
                this._currentStartSize2 = this._startSizeGradients[1].getFactor();
            }

            return this;
        }

        /**
         * Remove a specific start size gradient
         * @param gradient defines the gradient to remove
         * @returns the current particle system
         */
        public removeStartSizeGradient(gradient: number): IParticleSystem {
            this._removeFactorGradient(this._emitRateGradients, gradient);

            return this;
        } 

        /**
         * Adds a new color gradient
         * @param gradient defines the gradient to use (between 0 and 1)
         * @param color defines the color to affect to the specified gradient
         * @param color2 defines an additional color used to define a range ([color, color2]) with main color to pick the final color from
         */
        public addColorGradient(gradient: number, color: Color4, color2?: Color4): IParticleSystem {
            if (!this._colorGradients) {
                this._colorGradients = [];
            }

            let colorGradient = new ColorGradient();
            colorGradient.gradient = gradient;
            colorGradient.color1 = color;
            colorGradient.color2 = color2;
            this._colorGradients.push(colorGradient);

            this._colorGradients.sort((a, b) => {
                if (a.gradient < b.gradient) {
                    return -1;
                } else if (a.gradient > b.gradient) {
                    return 1;
                }

                return 0;
            });

            return this;
        }

        /**
         * Remove a specific color gradient
         * @param gradient defines the gradient to remove
         */
        public removeColorGradient(gradient: number): IParticleSystem {
            if (!this._colorGradients) {
                return this;
            }

            let index = 0;
            for (var colorGradient of this._colorGradients) {
                if (colorGradient.gradient === gradient) {
                    this._colorGradients.splice(index, 1);
                    break;
                }
                index++;
            }

            return this;
        }


        private _fetchR(u: number, v: number, width: number, height: number, pixels: Uint8Array): number {
            u = Math.abs(u) * 0.5 + 0.5;
            v = Math.abs(v) * 0.5 + 0.5;

            let wrappedU = ((u * width) % width) | 0;
            let wrappedV = ((v * height) % height) | 0;

            let position = (wrappedU + wrappedV * width) * 4;
            return pixels[position] / 255;
        }     

        protected _reset() {
            this._resetEffect();
        }

        private _resetEffect() {
            if (this._vertexBuffer) {
                this._vertexBuffer.dispose();
                this._vertexBuffer = null;
            }

            if (this._spriteBuffer) {
                this._spriteBuffer.dispose();
                this._spriteBuffer = null;
            }            

            this._createVertexBuffers();           
        }

        private _createVertexBuffers() {
            this._vertexBufferSize = this._useInstancing ? 10 : 12;
            if (this._isAnimationSheetEnabled) {
                this._vertexBufferSize += 1;
            }

            if (!this._isBillboardBased) {
                this._vertexBufferSize += 3;
            }

            let engine = this._scene.getEngine();
            this._vertexData = new Float32Array(this._capacity * this._vertexBufferSize * (this._useInstancing ? 1 : 4));
            this._vertexBuffer = new Buffer(engine, this._vertexData, true, this._vertexBufferSize);

            let dataOffset = 0;        
            var positions = this._vertexBuffer.createVertexBuffer(VertexBuffer.PositionKind, dataOffset, 3, this._vertexBufferSize, this._useInstancing);
            this._vertexBuffers[VertexBuffer.PositionKind] = positions;
            dataOffset += 3;

            var colors = this._vertexBuffer.createVertexBuffer(VertexBuffer.ColorKind, dataOffset, 4, this._vertexBufferSize, this._useInstancing);
            this._vertexBuffers[VertexBuffer.ColorKind] = colors;
            dataOffset += 4;

            var options = this._vertexBuffer.createVertexBuffer("angle", dataOffset, 1, this._vertexBufferSize, this._useInstancing);
            this._vertexBuffers["angle"] = options;
            dataOffset += 1;
            
            var size = this._vertexBuffer.createVertexBuffer("size", dataOffset, 2, this._vertexBufferSize, this._useInstancing);
            this._vertexBuffers["size"] = size;
            dataOffset += 2;

            if (this._isAnimationSheetEnabled) {
                var cellIndexBuffer = this._vertexBuffer.createVertexBuffer("cellIndex", dataOffset, 1, this._vertexBufferSize, this._useInstancing);
                this._vertexBuffers["cellIndex"] = cellIndexBuffer;
                dataOffset += 1;
            }

            if (!this._isBillboardBased) {
                var directionBuffer = this._vertexBuffer.createVertexBuffer("direction", dataOffset, 3, this._vertexBufferSize, this._useInstancing);
                this._vertexBuffers["direction"] = directionBuffer;
                dataOffset += 3;
            }

            var offsets: VertexBuffer;
            if (this._useInstancing) {
                var spriteData = new Float32Array([0, 0, 1, 0, 1, 1, 0, 1]);  
                this._spriteBuffer = new Buffer(engine, spriteData, false, 2);  
                offsets = this._spriteBuffer.createVertexBuffer("offset", 0, 2);
            } else {
                offsets = this._vertexBuffer.createVertexBuffer("offset", dataOffset, 2, this._vertexBufferSize, this._useInstancing);
                dataOffset += 2;
            }
            this._vertexBuffers["offset"] = offsets;              
        }

        private _createIndexBuffer() {
            if (this._useInstancing) {
                return;
            }
            var indices = [];
            var index = 0;
            for (var count = 0; count < this._capacity; count++) {
                indices.push(index);
                indices.push(index + 1);
                indices.push(index + 2);
                indices.push(index);
                indices.push(index + 2);
                indices.push(index + 3);
                index += 4;
            }

            this._indexBuffer = this._scene.getEngine().createIndexBuffer(indices);
        }

        /**
         * Gets the maximum number of particles active at the same time.
         * @returns The max number of active particles.
         */
        public getCapacity(): number {
            return this._capacity;
        }

        /**
         * Gets whether there are still active particles in the system.
         * @returns True if it is alive, otherwise false.
         */
        public isAlive(): boolean {
            return this._alive;
        }

        /**
         * Gets if the system has been started. (Note: this will still be true after stop is called)
         * @returns True if it has been started, otherwise false.
         */
        public isStarted(): boolean {
            return this._started;
        }

        /**
         * Starts the particle system and begins to emit
         * @param delay defines the delay in milliseconds before starting the system (0 by default)
         */
        public start(delay = 0): void {
            if (delay) {
                setTimeout(()=> {
                    this.start(0);
                }, delay);
                return;
            }

            this._started = true;
            this._stopped = false;
            this._actualFrame = 0;
            if (this.subEmitters && this.subEmitters.length != 0) {
                this.activeSubSystems = new Array<ParticleSystem>();
            }

            if (this.preWarmCycles) {
                for (var index = 0; index < this.preWarmCycles; index++) {
                    this.animate(true);
                }
            }
        }

        /**
         * Stops the particle system.
         * @param stopSubEmitters if true it will stop the current system and all created sub-Systems if false it will stop the current root system only, this param is used by the root particle system only. the default value is true.
         */
        public stop(stopSubEmitters = true): void {
            this._stopped = true;

            if (stopSubEmitters) {
                this._stopSubEmitters();
            }
        }

        // animation sheet

        /**
         * Remove all active particles
         */
        public reset(): void {
            this._stockParticles = [];
            this._particles = [];
        }

        /**
         * @hidden (for internal use only)
         */
        public _appendParticleVertex(index: number, particle: Particle, offsetX: number, offsetY: number): void {
            var offset = index * this._vertexBufferSize;

            this._vertexData[offset++] = particle.position.x;
            this._vertexData[offset++] = particle.position.y;
            this._vertexData[offset++] = particle.position.z;
            this._vertexData[offset++] = particle.color.r;
            this._vertexData[offset++] = particle.color.g;
            this._vertexData[offset++] = particle.color.b;
            this._vertexData[offset++] = particle.color.a;
            this._vertexData[offset++] = particle.angle;

            this._vertexData[offset++] = particle.scale.x * particle.size;
            this._vertexData[offset++] = particle.scale.y * particle.size;
            
            if (this._isAnimationSheetEnabled) {
                this._vertexData[offset++] = particle.cellIndex;
            }

            if (!this._isBillboardBased) {
                if (particle._initialDirection) {
                    this._vertexData[offset++] = particle._initialDirection.x;
                    this._vertexData[offset++] = particle._initialDirection.y;
                    this._vertexData[offset++] = particle._initialDirection.z;
                } else {
                    this._vertexData[offset++] = particle.direction.x;
                    this._vertexData[offset++] = particle.direction.y;
                    this._vertexData[offset++] = particle.direction.z;
                }
            }

            if (!this._useInstancing) {
                if (this._isAnimationSheetEnabled) {
                    if (offsetX === 0)
                        offsetX = this._epsilon;
                    else if (offsetX === 1)
                        offsetX = 1 - this._epsilon;
    
                    if (offsetY === 0)
                        offsetY = this._epsilon;
                    else if (offsetY === 1)
                        offsetY = 1 - this._epsilon;
                }

                this._vertexData[offset++] = offsetX;
                this._vertexData[offset++] = offsetY;   
            }
        }

        // start of sub system methods

        /**
         * "Recycles" one of the particle by copying it back to the "stock" of particles and removing it from the active list.
         * Its lifetime will start back at 0.
         */
        public recycleParticle: (particle: Particle) => void = (particle) => {
            var lastParticle = <Particle>this._particles.pop();
            if (lastParticle !== particle) {
                lastParticle.copyTo(particle);
            }
            this._stockParticles.push(lastParticle);
        };

        private _stopSubEmitters(): void {
            if (!this.activeSubSystems) {
                return;
            }
            this.activeSubSystems.forEach(subSystem => {
                subSystem.stop(true);
            });
            this.activeSubSystems = new Array<ParticleSystem>();
        }

        private _createParticle: () => Particle = () => {
            var particle: Particle;
            if (this._stockParticles.length !== 0) {
                particle = <Particle>this._stockParticles.pop();
                particle._reset();
            } else {
                particle = new Particle(this);
            }
            return particle;
        }

        private _removeFromRoot(): void {
            if (!this._rootParticleSystem){
                return;
            }
            
            let index = this._rootParticleSystem.activeSubSystems.indexOf(this);
            if (index !== -1) {
                this._rootParticleSystem.activeSubSystems.splice(index, 1);
            }
        }

        private _emitFromParticle: (particle: Particle) => void = (particle) => {
            if (!this.subEmitters || this.subEmitters.length === 0) {
                return;
            }

            var templateIndex = Math.floor(Math.random() * this.subEmitters.length);

            var subSystem = this.subEmitters[templateIndex].clone(this.name + "_sub", particle.position.clone());
            subSystem._rootParticleSystem = this;
            this.activeSubSystems.push(subSystem);
            subSystem.start();
        }

        // End of sub system methods

        private _update(newParticles: number): void {
            // Update current
            this._alive = this._particles.length > 0;

            if ((<AbstractMesh>this.emitter).position) {
                var emitterMesh = (<AbstractMesh>this.emitter);
                this._emitterWorldMatrix = emitterMesh.getWorldMatrix();
            } else {
                var emitterPosition = (<Vector3>this.emitter);
                this._emitterWorldMatrix = Matrix.Translation(emitterPosition.x, emitterPosition.y, emitterPosition.z);
            }

            this.updateFunction(this._particles);

            // Add new ones
            var particle: Particle;
            for (var index = 0; index < newParticles; index++) {
                if (this._particles.length === this._capacity) {
                    break;
                }

                particle = this._createParticle();

                this._particles.push(particle);

                // Emitter
                let emitPower = Scalar.RandomRange(this.minEmitPower, this.maxEmitPower);

                if (this.startPositionFunction) {
                    this.startPositionFunction(this._emitterWorldMatrix, particle.position, particle);
                }
                else {
                    this.particleEmitterType.startPositionFunction(this._emitterWorldMatrix, particle.position, particle);
                }

                if (this.startDirectionFunction) {
                    this.startDirectionFunction(this._emitterWorldMatrix, particle.direction, particle);
                }
                else {
                    this.particleEmitterType.startDirectionFunction(this._emitterWorldMatrix, particle.direction, particle);
                }

                if (emitPower === 0) {
                    if (!particle._initialDirection) {
                        particle._initialDirection = particle.direction.clone();
                    } else {
                        particle._initialDirection.copyFrom(particle.direction);
                    }
                } else {
                    particle._initialDirection = null;
                }

                particle.direction.scaleInPlace(emitPower);

                // Life time
                if (this.targetStopDuration && this._lifeTimeGradients && this._lifeTimeGradients.length > 0) {
                    let ratio = Scalar.Clamp(this._actualFrame / this.targetStopDuration);
                    Tools.GetCurrentGradient(ratio, this._lifeTimeGradients, (currentGradient, nextGradient, scale) => {
                        let factorGradient1 = (<FactorGradient>currentGradient);
                        let factorGradient2 = (<FactorGradient>nextGradient);
                        let lifeTime1 = factorGradient1.getFactor(); 
                        let lifeTime2 = factorGradient2.getFactor(); 
                        let gradient = (ratio - factorGradient1.gradient) / (factorGradient2.gradient - factorGradient1.gradient);
                        particle.lifeTime = Scalar.Lerp(lifeTime1, lifeTime2, gradient);
                    });
                } else {
                    particle.lifeTime = Scalar.RandomRange(this.minLifeTime, this.maxLifeTime);
                }

                // Size
                if (!this._sizeGradients || this._sizeGradients.length === 0) {
                    particle.size = Scalar.RandomRange(this.minSize, this.maxSize);
                } else {
                    particle._currentSizeGradient = this._sizeGradients[0];
                    particle._currentSize1 = particle._currentSizeGradient.getFactor();
                    particle.size = particle._currentSize1;

                    if (this._sizeGradients.length > 1) {
                        particle._currentSize2 = this._sizeGradients[1].getFactor();
                    } else {
                        particle._currentSize2 = particle._currentSize1;
                    }
                }
                // Size and scale
                particle.scale.copyFromFloats(Scalar.RandomRange(this.minScaleX, this.maxScaleX), Scalar.RandomRange(this.minScaleY, this.maxScaleY));
                
                // Adjust scale by start size
                if(this._startSizeGradients && this._startSizeGradients[0]){
                    const ratio = this._actualFrame / this.targetStopDuration;            
                    Tools.GetCurrentGradient(ratio, this._startSizeGradients, (currentGradient, nextGradient, scale) => {
                        if (currentGradient !== this._currentStartSizeGradient) {
                            this._currentStartSize1 = this._currentStartSize2;
                            this._currentStartSize2 = (<FactorGradient>nextGradient).getFactor();    
                            this._currentStartSizeGradient = (<FactorGradient>currentGradient);
                        }                                
                        
                        var value = Scalar.Lerp(this._currentStartSize1, this._currentStartSize2, scale);
                        particle.scale.scaleInPlace(value);
                    });
                }

                // Angle
                if (!this._angularSpeedGradients || this._angularSpeedGradients.length === 0) {
                    particle.angularSpeed = Scalar.RandomRange(this.minAngularSpeed, this.maxAngularSpeed);
                } else {
                    particle._currentAngularSpeedGradient = this._angularSpeedGradients[0];
                    particle.angularSpeed =  particle._currentAngularSpeedGradient.getFactor();
                    particle._currentAngularSpeed1 = particle.angularSpeed;

                    if (this._angularSpeedGradients.length > 1) {
                        particle._currentAngularSpeed2 = this._angularSpeedGradients[1].getFactor();
                    } else {
                        particle._currentAngularSpeed2 = particle._currentAngularSpeed1;
                    }
                }
                particle.angle = Scalar.RandomRange(this.minInitialRotation, this.maxInitialRotation);

                // Velocity
                if (this._velocityGradients && this._velocityGradients.length > 0) {
                    particle._currentVelocityGradient = this._velocityGradients[0];
                    particle._currentVelocity1 = particle._currentVelocityGradient.getFactor();

                    if (this._velocityGradients.length > 1) {
                        particle._currentVelocity2 = this._velocityGradients[1].getFactor();
                    } else {
                        particle._currentVelocity2 = particle._currentVelocity1;
                    }
                }        
                
                // Limit velocity
                if (this._limitVelocityGradients && this._limitVelocityGradients.length > 0) {
                    particle._currentLimitVelocityGradient = this._limitVelocityGradients[0];
                    particle._currentLimitVelocity1 = particle._currentLimitVelocityGradient.getFactor();

                    if (this._limitVelocityGradients.length > 1) {
                        particle._currentLimitVelocity2 = this._limitVelocityGradients[1].getFactor();
                    } else {
                        particle._currentLimitVelocity2 = particle._currentLimitVelocity1;
                    }
                }                   

                // Drag
                if (this._dragGradients && this._dragGradients.length > 0) {
                    particle._currentDragGradient = this._dragGradients[0];
                    particle._currentDrag1 = particle._currentDragGradient.getFactor();

                    if (this._dragGradients.length > 1) {
                        particle._currentDrag2 = this._dragGradients[1].getFactor();
                    } else {
                        particle._currentDrag2 = particle._currentDrag1;
                    }
                }            

                // Color
                if (!this._colorGradients || this._colorGradients.length === 0) {
                    var step = Scalar.RandomRange(0, 1.0);

                    Color4.LerpToRef(this.color1, this.color2, step, particle.color);

                    this.colorDead.subtractToRef(particle.color, this._colorDiff);
                    this._colorDiff.scaleToRef(1.0 / particle.lifeTime, particle.colorStep);
                } else {
                    particle._currentColorGradient = this._colorGradients[0];
                    particle._currentColorGradient.getColorToRef(particle.color);
                    particle._currentColor1.copyFrom(particle.color);

                    if (this._colorGradients.length > 1) {
                        this._colorGradients[1].getColorToRef(particle._currentColor2);
                    } else {
                        particle._currentColor2.copyFrom(particle.color);
                    }
                }

                // Sheet
                if (this._isAnimationSheetEnabled) {
                    particle._initialStartSpriteCellID = this.startSpriteCellID;
                    particle._initialEndSpriteCellID = this.endSpriteCellID;
                }
            }
        }

        /** @hidden */
        public static _GetAttributeNamesOrOptions(isAnimationSheetEnabled = false, isBillboardBased = false): string[] {
            var attributeNamesOrOptions = [VertexBuffer.PositionKind, VertexBuffer.ColorKind, "angle", "offset", "size"];

            if (isAnimationSheetEnabled) {
                attributeNamesOrOptions.push("cellIndex");
            }

            if (!isBillboardBased) {
                attributeNamesOrOptions.push("direction");
            }            

            return attributeNamesOrOptions;
        }

        public static _GetEffectCreationOptions(isAnimationSheetEnabled = false): string[] {
            var effectCreationOption = ["invView", "view", "projection", "vClipPlane", "vClipPlane2", "vClipPlane3", "vClipPlane4", "textureMask", "translationPivot", "eyePosition"];

            if (isAnimationSheetEnabled) {
                effectCreationOption.push("particlesInfos")
            }

            return effectCreationOption;
        }

        private _getEffect(): Effect {
            if (this._customEffect) {
                return this._customEffect;
            };

            var defines = [];

            if (this._scene.clipPlane) {
                defines.push("#define CLIPPLANE");
            }

            if (this._scene.clipPlane2) {
                defines.push("#define CLIPPLANE2");
            }
            
            if (this._scene.clipPlane3) {
                defines.push("#define CLIPPLANE3");
            }
            
            if (this._scene.clipPlane4) {
                defines.push("#define CLIPPLANE4");
            }            

            if (this._isAnimationSheetEnabled) {
                defines.push("#define ANIMATESHEET");
            }

            if (this.blendMode === ParticleSystem.BLENDMODE_MULTIPLY) {
                defines.push("#define BLENDMULTIPLYMODE");
            }

            if (this._isBillboardBased) {
                defines.push("#define BILLBOARD");

                switch (this.billboardMode) {
                    case AbstractMesh.BILLBOARDMODE_Y:
                        defines.push("#define BILLBOARDY");
                        break;
                    case AbstractMesh.BILLBOARDMODE_ALL:
                    default:
                        break;
                }
            }

            if (this._imageProcessingConfiguration) {
                this._imageProcessingConfiguration.prepareDefines(this._imageProcessingConfigurationDefines);
                defines.push(this._imageProcessingConfigurationDefines.toString());
            }

            // Effect
            var join = defines.join("\n");
            if (this._cachedDefines !== join) {
                this._cachedDefines = join;

                var attributesNamesOrOptions = ParticleSystem._GetAttributeNamesOrOptions(this._isAnimationSheetEnabled, this._isBillboardBased);
                var effectCreationOption = ParticleSystem._GetEffectCreationOptions(this._isAnimationSheetEnabled);

                var samplers = ["diffuseSampler"];

                if (ImageProcessingConfiguration) {
                    ImageProcessingConfiguration.PrepareUniforms(effectCreationOption, this._imageProcessingConfigurationDefines);
                    ImageProcessingConfiguration.PrepareSamplers(samplers, this._imageProcessingConfigurationDefines);
                }

                this._effect = this._scene.getEngine().createEffect(
                    "particles",
                    attributesNamesOrOptions,
                    effectCreationOption,
                    ["diffuseSampler"], join);
            }

            return this._effect;
        }

        /**
         * Animates the particle system for the current frame by emitting new particles and or animating the living ones.
         * @param preWarmOnly will prevent the system from updating the vertex buffer (default is false)
         */
        public animate(preWarmOnly = false): void {
            if (!this._started)
                return;

            if (!preWarmOnly) {
                var effect = this._getEffect();

                // Check
                if (!this.emitter || !this._imageProcessingConfiguration.isReady() || !effect.isReady() || !this.particleTexture || !this.particleTexture.isReady())
                    return;

                if (this._currentRenderId === this._scene.getRenderId()) {
                    return;
                }
                this._currentRenderId = this._scene.getRenderId();
            }

            this._scaledUpdateSpeed = this.updateSpeed * (preWarmOnly ? this.preWarmStepOffset : this._scene.getAnimationRatio());

            // Determine the number of particles we need to create
            var newParticles;

            if (this.manualEmitCount > -1) {
                newParticles = this.manualEmitCount;
                this._newPartsExcess = 0;
                this.manualEmitCount = 0;
            } else {
                let rate = this.emitRate;

                if (this._emitRateGradients && this._emitRateGradients.length > 0 && this.targetStopDuration) {   
                    const ratio = this._actualFrame / this.targetStopDuration;               
                    Tools.GetCurrentGradient(ratio, this._emitRateGradients, (currentGradient, nextGradient, scale) => {
                        if (currentGradient !== this._currentEmitRateGradient) {
                            this._currentEmitRate1 = this._currentEmitRate2;
                            this._currentEmitRate2 = (<FactorGradient>nextGradient).getFactor();    
                            this._currentEmitRateGradient = (<FactorGradient>currentGradient);
                        }                                
                        
                        rate = Scalar.Lerp(this._currentEmitRate1, this._currentEmitRate2, scale);
                    });
                }                   

                newParticles = ((rate * this._scaledUpdateSpeed) >> 0);
                this._newPartsExcess += rate * this._scaledUpdateSpeed - newParticles;
            }

            if (this._newPartsExcess > 1.0) {
                newParticles += this._newPartsExcess >> 0;
                this._newPartsExcess -= this._newPartsExcess >> 0;
            }

            this._alive = false;

            if (!this._stopped) {
                this._actualFrame += this._scaledUpdateSpeed;

                if (this.targetStopDuration && this._actualFrame >= this.targetStopDuration)
                    this.stop();
            } else {
                newParticles = 0;
            }
            this._update(newParticles);

            // Stopped?
            if (this._stopped) {
                if (!this._alive) {
                    this._started = false;
                    if (this.onAnimationEnd) {
                        this.onAnimationEnd();
                    }
                    if (this.disposeOnStop) {
                        this._scene._toBeDisposed.push(this);
                    }
                }
            }

            if (!preWarmOnly) {
                // Update VBO
                var offset = 0;
                for (var index = 0; index < this._particles.length; index++) {
                    var particle = this._particles[index];
                    this._appendParticleVertices(offset, particle);                
                    offset += this._useInstancing ? 1 : 4;
                }

                if (this._vertexBuffer) {
                    this._vertexBuffer.update(this._vertexData);
                }
            }

            if (this.manualEmitCount === 0 && this.disposeOnStop) {
                this.stop();
            }
        }

        private _appendParticleVertices(offset: number, particle: Particle) {
            this._appendParticleVertex(offset++, particle, 0, 0);
            if (!this._useInstancing) {
                this._appendParticleVertex(offset++, particle, 1, 0);
                this._appendParticleVertex(offset++, particle, 1, 1);
                this._appendParticleVertex(offset++, particle, 0, 1);
            }
        }

        /**
         * Rebuilds the particle system.
         */
        public rebuild(): void {
            this._createIndexBuffer();

            if (this._vertexBuffer) {
                this._vertexBuffer._rebuild();
            }
        }

        /**
         * Is this system ready to be used/rendered
         * @return true if the system is ready
         */
        public isReady(): boolean {
            var effect = this._getEffect();
            if (!this.emitter || !this._imageProcessingConfiguration.isReady() || !effect.isReady() || !this.particleTexture || !this.particleTexture.isReady()) {
                return false;
            }

            return true;
        }

        /**
         * Renders the particle system in its current state.
         * @returns the current number of particles
         */
        public render(): number {
            var effect = this._getEffect();

            // Check
            if (!this.isReady() || !this._particles.length) {
                return 0;
            }

            var engine = this._scene.getEngine();

            // Render
            engine.enableEffect(effect);
            engine.setState(false);

            var viewMatrix = this._scene.getViewMatrix();
            effect.setTexture("diffuseSampler", this.particleTexture);
            effect.setMatrix("view", viewMatrix);
            effect.setMatrix("projection", this._scene.getProjectionMatrix());

            if (this._isAnimationSheetEnabled && this.particleTexture) {
                var baseSize = this.particleTexture.getBaseSize();
                effect.setFloat3("particlesInfos", this.spriteCellWidth / baseSize.width, this.spriteCellHeight / baseSize.height, baseSize.width / this.spriteCellWidth);
            }

            effect.setVector2("translationPivot", this.translationPivot);
            effect.setFloat4("textureMask", this.textureMask.r, this.textureMask.g, this.textureMask.b, this.textureMask.a);

            if (this._isBillboardBased) {
                var camera = this._scene.activeCamera!;
                effect.setVector3("eyePosition", camera.globalPosition);
            }

            if (this._scene.clipPlane || this._scene.clipPlane2 || this._scene.clipPlane3 || this._scene.clipPlane4) {
                var invView = viewMatrix.clone();
                invView.invert();
                effect.setMatrix("invView", invView);
                MaterialHelper.BindClipPlane(effect, this._scene);
            }

            engine.bindBuffers(this._vertexBuffers, this._indexBuffer, effect);

            // image processing
            if (this._imageProcessingConfiguration && !this._imageProcessingConfiguration.applyByPostProcess) {
                this._imageProcessingConfiguration.bind(effect);
            }

            // Draw order
            switch(this.blendMode)
            {
                case ParticleSystem.BLENDMODE_ADD:
                    engine.setAlphaMode(Engine.ALPHA_ADD);
                    break;
                case ParticleSystem.BLENDMODE_ONEONE:
                    engine.setAlphaMode(Engine.ALPHA_ONEONE);
                    break;
                case ParticleSystem.BLENDMODE_STANDARD:
                    engine.setAlphaMode(Engine.ALPHA_COMBINE);
                    break;
                case ParticleSystem.BLENDMODE_MULTIPLY:
                    engine.setAlphaMode(Engine.ALPHA_MULTIPLY);
                    break;                    
            }

            if (this.forceDepthWrite) {
                engine.setDepthWrite(true);
            }

            if (this._useInstancing) {
                engine.drawArraysType(Material.TriangleFanDrawMode, 0, 4, this._particles.length);  
                engine.unbindInstanceAttributes();
            } else {
                engine.drawElementsType(Material.TriangleFillMode, 0, this._particles.length * 6);
            }
            engine.setAlphaMode(Engine.ALPHA_DISABLE);

            return this._particles.length;
        }

        /**
         * Disposes the particle system and free the associated resources
         * @param disposeTexture defines if the particule texture must be disposed as well (true by default)
         */
        public dispose(disposeTexture = true): void {
            if (this._vertexBuffer) {
                this._vertexBuffer.dispose();
                this._vertexBuffer = null;
            }

            if (this._spriteBuffer) {
                this._spriteBuffer.dispose();
                this._spriteBuffer = null;
            }

            if (this._indexBuffer) {
                this._scene.getEngine()._releaseBuffer(this._indexBuffer);
                this._indexBuffer = null;
            }

            if (disposeTexture && this.particleTexture) {
                this.particleTexture.dispose();
                this.particleTexture = null;
            }

            if (disposeTexture && this.noiseTexture) {
                this.noiseTexture.dispose();
                this.noiseTexture = null;
            }

            this._removeFromRoot();

            // Remove from scene
            var index = this._scene.particleSystems.indexOf(this);
            if (index > -1) {
                this._scene.particleSystems.splice(index, 1);
            }

            // Callback
            this.onDisposeObservable.notifyObservers(this);
            this.onDisposeObservable.clear();
        }

        // Clone
        /**
         * Clones the particle system.
         * @param name The name of the cloned object
         * @param newEmitter The new emitter to use
         * @returns the cloned particle system
         */
        public clone(name: string, newEmitter: any): ParticleSystem {
            var custom: Nullable<Effect> = null;
            var program: any = null;
            if (this.customShader != null) {
                program = this.customShader;
                var defines: string = (program.shaderOptions.defines.length > 0) ? program.shaderOptions.defines.join("\n") : "";
                custom = this._scene.getEngine().createEffectForParticles(program.shaderPath.fragmentElement, program.shaderOptions.uniforms, program.shaderOptions.samplers, defines);
            } else if (this._customEffect) {
                custom = this._customEffect;
            }
            var result = new ParticleSystem(name, this._capacity, this._scene, custom);
            result.customShader = program;

            Tools.DeepCopy(this, result, ["particles", "customShader"]);

            if (newEmitter === undefined) {
                newEmitter = this.emitter;
            }

            result.emitter = newEmitter;
            if (this.particleTexture) {
                result.particleTexture = new Texture(this.particleTexture.url, this._scene);
            }

            if (!this.preventAutoStart) {
                result.start();
            }

            return result;
        }

        /**
         * Serializes the particle system to a JSON object.
         * @returns the JSON object
         */
        public serialize(): any {
            var serializationObject: any = {};

            ParticleSystem._Serialize(serializationObject, this);

            serializationObject.textureMask = this.textureMask.asArray();
            serializationObject.customShader = this.customShader;
            serializationObject.preventAutoStart = this.preventAutoStart;

            serializationObject.isAnimationSheetEnabled = this._isAnimationSheetEnabled;

            return serializationObject;
        }

        /** @hidden */
        public static _Serialize(serializationObject: any, particleSystem: IParticleSystem) {
            serializationObject.name = particleSystem.name;
            serializationObject.id = particleSystem.id;

            serializationObject.capacity = particleSystem.getCapacity();

            // Emitter
            if ((<AbstractMesh>particleSystem.emitter).position) {
                var emitterMesh = (<AbstractMesh>particleSystem.emitter);
                serializationObject.emitterId = emitterMesh.id;
            } else {
                var emitterPosition = (<Vector3>particleSystem.emitter);
                serializationObject.emitter = emitterPosition.asArray();
            }

            // Emitter
            if (particleSystem.particleEmitterType) {
                serializationObject.particleEmitterType = particleSystem.particleEmitterType.serialize();
            }           
            
            if (particleSystem.particleTexture) {
                serializationObject.textureName = particleSystem.particleTexture.name;
            }
           
            // Animations
            Animation.AppendSerializedAnimations(particleSystem, serializationObject);

            // Particle system
            serializationObject.renderingGroupId = particleSystem.renderingGroupId;
            serializationObject.isBillboardBased = particleSystem.isBillboardBased;
            serializationObject.minAngularSpeed = particleSystem.minAngularSpeed;
            serializationObject.maxAngularSpeed = particleSystem.maxAngularSpeed;
            serializationObject.minSize = particleSystem.minSize;
            serializationObject.maxSize = particleSystem.maxSize;
            serializationObject.minScaleX = particleSystem.minScaleX;
            serializationObject.maxScaleX = particleSystem.maxScaleX;
            serializationObject.minScaleY = particleSystem.minScaleY;
            serializationObject.maxScaleY = particleSystem.maxScaleY;            
            serializationObject.minEmitPower = particleSystem.minEmitPower;
            serializationObject.maxEmitPower = particleSystem.maxEmitPower;
            serializationObject.minLifeTime = particleSystem.minLifeTime;
            serializationObject.maxLifeTime = particleSystem.maxLifeTime;
            serializationObject.emitRate = particleSystem.emitRate;
            serializationObject.gravity = particleSystem.gravity.asArray();
            serializationObject.noiseStrength = particleSystem.noiseStrength.asArray();
            serializationObject.color1 = particleSystem.color1.asArray();
            serializationObject.color2 = particleSystem.color2.asArray();
            serializationObject.colorDead = particleSystem.colorDead.asArray();
            serializationObject.updateSpeed = particleSystem.updateSpeed;
            serializationObject.targetStopDuration = particleSystem.targetStopDuration;
            serializationObject.blendMode = particleSystem.blendMode;
            serializationObject.preWarmCycles = particleSystem.preWarmCycles;
            serializationObject.preWarmStepOffset = particleSystem.preWarmStepOffset;
            serializationObject.minInitialRotation = particleSystem.minInitialRotation;
            serializationObject.maxInitialRotation = particleSystem.maxInitialRotation;
            serializationObject.startSpriteCellID = particleSystem.startSpriteCellID;
            serializationObject.endSpriteCellID = particleSystem.endSpriteCellID;
            serializationObject.spriteCellChangeSpeed = particleSystem.spriteCellChangeSpeed;
            serializationObject.spriteCellWidth = particleSystem.spriteCellWidth;
            serializationObject.spriteCellHeight = particleSystem.spriteCellHeight;            

            let colorGradients = particleSystem.getColorGradients();
            if (colorGradients) {
                serializationObject.colorGradients = [];
                for (var colorGradient of colorGradients) {
                    var serializedGradient: any = {
                        gradient: colorGradient.gradient,
                        color1: colorGradient.color1.asArray()
                    };

                    if (colorGradient.color2) {
                        serializedGradient.color2 = colorGradient.color2.asArray();
                    }

                    serializationObject.colorGradients.push(serializedGradient);
                }
            }

            let sizeGradients = particleSystem.getSizeGradients();
            if (sizeGradients) {
                serializationObject.sizeGradients = [];
                for (var sizeGradient of sizeGradients) {

                    var serializedGradient: any = {
                        gradient: sizeGradient.gradient,
                        factor1: sizeGradient.factor1
                    };

                    if (sizeGradient.factor2 !== undefined) {
                        serializedGradient.factor2 = sizeGradient.factor2;
                    }

                    serializationObject.sizeGradients.push(serializedGradient);
                }
            }       
                        
            let angularSpeedGradients = particleSystem.getAngularSpeedGradients();
            if (angularSpeedGradients) {
                serializationObject.angularSpeedGradients = [];
                for (var angularSpeedGradient of angularSpeedGradients) {

                    var serializedGradient: any = {
                        gradient: angularSpeedGradient.gradient,
                        factor1: angularSpeedGradient.factor1
                    };

                    if (angularSpeedGradient.factor2 !== undefined) {
                        serializedGradient.factor2 = angularSpeedGradient.factor2;
                    }

                    serializationObject.angularSpeedGradients.push(serializedGradient);
                }
            }  

            let velocityGradients = particleSystem.getVelocityGradients();
            if (velocityGradients) {
                serializationObject.velocityGradients = [];
                for (var velocityGradient of velocityGradients) {

                    var serializedGradient: any = {
                        gradient: velocityGradient.gradient,
                        factor1: velocityGradient.factor1
                    };

                    if (velocityGradient.factor2 !== undefined) {
                        serializedGradient.factor2 = velocityGradient.factor2;
                    }

                    serializationObject.velocityGradients.push(serializedGradient);
                }
            }    

            let dragGradients = particleSystem.getDragGradients();
            if (dragGradients) {
                serializationObject.dragyGradients = [];
                for (var dragGradient of dragGradients) {

                    var serializedGradient: any = {
                        gradient: dragGradient.gradient,
                        factor1: dragGradient.factor1
                    };

                    if (dragGradient.factor2 !== undefined) {
                        serializedGradient.factor2 = dragGradient.factor2;
                    }

                    serializationObject.dragGradients.push(serializedGradient);
                }
            }    
            
            let emitRateGradients = particleSystem.getEmitRateGradients();
            if (emitRateGradients) {
                serializationObject.emitRateGradients = [];
                for (var emitRateGradient of emitRateGradients) {

                    var serializedGradient: any = {
                        gradient: emitRateGradient.gradient,
                        factor1: emitRateGradient.factor1
                    };

                    if (emitRateGradient.factor2 !== undefined) {
                        serializedGradient.factor2 = emitRateGradient.factor2;
                    }

                    serializationObject.emitRateGradients.push(serializedGradient);
                }
            } 
            
            let startSizeGradients = particleSystem.getStartSizeGradients();
            if (startSizeGradients) {
                serializationObject.startSizeGradients = [];
                for (var startSizeGradient of startSizeGradients) {

                    var serializedGradient: any = {
                        gradient: startSizeGradient.gradient,
                        factor1: startSizeGradient.factor1
                    };

                    if (startSizeGradient.factor2 !== undefined) {
                        serializedGradient.factor2 = startSizeGradient.factor2;
                    }

                    serializationObject.startSizeGradients.push(serializedGradient);
                }
            } 

            let limitVelocityGradients = particleSystem.getLimitVelocityGradients();
            if (limitVelocityGradients) {
                serializationObject.limitVelocityGradients = [];
                for (var limitVelocityGradient of limitVelocityGradients) {

                    var serializedGradient: any = {
                        gradient: limitVelocityGradient.gradient,
                        factor1: limitVelocityGradient.factor1
                    };

                    if (limitVelocityGradient.factor2 !== undefined) {
                        serializedGradient.factor2 = limitVelocityGradient.factor2;
                    }

                    serializationObject.limitVelocityGradients.push(serializedGradient);
                }

                serializationObject.limitVelocityDamping = particleSystem.limitVelocityDamping;
            }   
            
            if (ProceduralTexture && particleSystem.noiseTexture && particleSystem.noiseTexture instanceof ProceduralTexture) {
                const noiseTexture = particleSystem.noiseTexture as ProceduralTexture;
                serializationObject.noiseTexture = noiseTexture.serialize();
            }
        }

        /** @hidden */
        public static _Parse(parsedParticleSystem: any, particleSystem: IParticleSystem, scene: Scene, rootUrl: string) {
            // Texture
            if (parsedParticleSystem.textureName) {
                particleSystem.particleTexture = new Texture(rootUrl + parsedParticleSystem.textureName, scene);
                particleSystem.particleTexture.name = parsedParticleSystem.textureName;
            }

            // Emitter
            if (parsedParticleSystem.emitterId === undefined) {
                particleSystem.emitter = Vector3.Zero();
            }
             else if (parsedParticleSystem.emitterId) {
                particleSystem.emitter = scene.getLastMeshByID(parsedParticleSystem.emitterId);
            } else {
                particleSystem.emitter = Vector3.FromArray(parsedParticleSystem.emitter);
            }

            // Misc.
            if (parsedParticleSystem.renderingGroupId !== undefined) {
                particleSystem.renderingGroupId = parsedParticleSystem.renderingGroupId;
            }

            if (parsedParticleSystem.isBillboardBased !== undefined) {
                particleSystem.isBillboardBased = parsedParticleSystem.isBillboardBased;
            }

            // Animations
            if (parsedParticleSystem.animations) {
                for (var animationIndex = 0; animationIndex < parsedParticleSystem.animations.length; animationIndex++) {
                    var parsedAnimation = parsedParticleSystem.animations[animationIndex];
                    particleSystem.animations.push(Animation.Parse(parsedAnimation));
                }
            }

            if (parsedParticleSystem.autoAnimate) {
                scene.beginAnimation(particleSystem, parsedParticleSystem.autoAnimateFrom, parsedParticleSystem.autoAnimateTo, parsedParticleSystem.autoAnimateLoop, parsedParticleSystem.autoAnimateSpeed || 1.0);
            }

            // Particle system
            particleSystem.minAngularSpeed = parsedParticleSystem.minAngularSpeed;
            particleSystem.maxAngularSpeed = parsedParticleSystem.maxAngularSpeed;
            particleSystem.minSize = parsedParticleSystem.minSize;
            particleSystem.maxSize = parsedParticleSystem.maxSize;

            if (parsedParticleSystem.minScaleX) {
                particleSystem.minScaleX = parsedParticleSystem.minScaleX;
                particleSystem.maxScaleX = parsedParticleSystem.maxScaleX;                
                particleSystem.minScaleY = parsedParticleSystem.minScaleY;
                particleSystem.maxScaleY = parsedParticleSystem.maxScaleY;                
            }

            if (parsedParticleSystem.preWarmCycles !== undefined) {
                particleSystem.preWarmCycles = parsedParticleSystem.preWarmCycles;
                particleSystem.preWarmStepOffset = parsedParticleSystem.preWarmStepOffset;
            }   

            if (parsedParticleSystem.minInitialRotation !== undefined) {
                particleSystem.minInitialRotation = parsedParticleSystem.minInitialRotation;
                particleSystem.maxInitialRotation = parsedParticleSystem.maxInitialRotation;
            }

            particleSystem.minLifeTime = parsedParticleSystem.minLifeTime;
            particleSystem.maxLifeTime = parsedParticleSystem.maxLifeTime;
            particleSystem.minEmitPower = parsedParticleSystem.minEmitPower;
            particleSystem.maxEmitPower = parsedParticleSystem.maxEmitPower;
            particleSystem.emitRate = parsedParticleSystem.emitRate;
            particleSystem.gravity = Vector3.FromArray(parsedParticleSystem.gravity);
            if (parsedParticleSystem.noiseStrength) {
                particleSystem.noiseStrength = Vector3.FromArray(parsedParticleSystem.noiseStrength);
            }
            particleSystem.color1 = Color4.FromArray(parsedParticleSystem.color1);
            particleSystem.color2 = Color4.FromArray(parsedParticleSystem.color2);
            particleSystem.colorDead = Color4.FromArray(parsedParticleSystem.colorDead);
            particleSystem.updateSpeed = parsedParticleSystem.updateSpeed;
            particleSystem.targetStopDuration = parsedParticleSystem.targetStopDuration;
            particleSystem.blendMode = parsedParticleSystem.blendMode;


            if (parsedParticleSystem.colorGradients) {
                for (var colorGradient of parsedParticleSystem.colorGradients) {
                    particleSystem.addColorGradient(colorGradient.gradient, Color4.FromArray(colorGradient.color1), colorGradient.color2 ? Color4.FromArray(colorGradient.color2) : undefined);
                }
            }

            if (parsedParticleSystem.sizeGradients) {
                for (var sizeGradient of parsedParticleSystem.sizeGradients) {
                    particleSystem.addSizeGradient(sizeGradient.gradient, sizeGradient.factor1 !== undefined ?  sizeGradient.factor1 : sizeGradient.factor, sizeGradient.factor2);
                }
            }       

            if (parsedParticleSystem.angularSpeedGradients) {
                for (var angularSpeedGradient of parsedParticleSystem.angularSpeedGradients) {
                    particleSystem.addAngularSpeedGradient(angularSpeedGradient.gradient, angularSpeedGradient.factor1 !== undefined ?  angularSpeedGradient.factor1 : angularSpeedGradient.factor, angularSpeedGradient.factor2);
                }
            }       
            
            if (parsedParticleSystem.velocityGradients) {
                for (var velocityGradient of parsedParticleSystem.velocityGradients) {
                    particleSystem.addVelocityGradient(velocityGradient.gradient, velocityGradient.factor1 !== undefined ?  velocityGradient.factor1 : velocityGradient.factor, velocityGradient.factor2);
                }
            }     

            if (parsedParticleSystem.dragGradients) {
                for (var dragGradient of parsedParticleSystem.dragGradients) {
                    particleSystem.addDragGradient(dragGradient.gradient, dragGradient.factor1 !== undefined ?  dragGradient.factor1 : dragGradient.factor, dragGradient.factor2);
                }
            }        
            
            if (parsedParticleSystem.emitRateGradients) {
                for (var emitRateGradient of parsedParticleSystem.emitRateGradients) {
                    particleSystem.addEmitRateGradient(emitRateGradient.gradient, emitRateGradient.factor1 !== undefined ?  emitRateGradient.factor1 : emitRateGradient.factor, emitRateGradient.factor2);
                }
            } 
            
            if (parsedParticleSystem.startSizeGradients) {
                for (var startSizeGradient of parsedParticleSystem.startSizeGradients) {
                    particleSystem.addStartSizeGradient(startSizeGradient.gradient, startSizeGradient.factor1 !== undefined ?  startSizeGradient.factor1 : startSizeGradient.factor, startSizeGradient.factor2);
                }
            }

            if (parsedParticleSystem.limitVelocityGradients) {
                for (var limitVelocityGradient of parsedParticleSystem.limitVelocityGradients) {
                    particleSystem.addLimitVelocityGradient(limitVelocityGradient.gradient, limitVelocityGradient.factor1 !== undefined ?  limitVelocityGradient.factor1 : limitVelocityGradient.factor, limitVelocityGradient.factor2);
                }
                particleSystem.limitVelocityDamping = parsedParticleSystem.limitVelocityDamping;
            }               
            
            if (parsedParticleSystem.noiseTexture) {
                particleSystem.noiseTexture = ProceduralTexture.Parse(parsedParticleSystem.noiseTexture, scene, rootUrl);
            }
            
            // Emitter
            let emitterType: IParticleEmitterType;
            if (parsedParticleSystem.particleEmitterType) {
                switch (parsedParticleSystem.particleEmitterType.type) {
                    case "SphereParticleEmitter":
                        emitterType = new SphereParticleEmitter();
                        break;
                    case "SphereDirectedParticleEmitter":
                        emitterType = new SphereDirectedParticleEmitter();
                        break;
                    case "ConeEmitter":
                    case "ConeParticleEmitter":
                        emitterType = new ConeParticleEmitter();
                        break;
                    case "BoxEmitter":
                    case "BoxParticleEmitter":
                    default:
                        emitterType = new BoxParticleEmitter();
                        break;                                                
                }

                emitterType.parse(parsedParticleSystem.particleEmitterType);
            } else {
                emitterType = new BoxParticleEmitter();
                emitterType.parse(parsedParticleSystem);
            }
            particleSystem.particleEmitterType = emitterType;

            // Animation sheet
            particleSystem.startSpriteCellID = parsedParticleSystem.startSpriteCellID;
            particleSystem.endSpriteCellID = parsedParticleSystem.endSpriteCellID;
            particleSystem.spriteCellWidth = parsedParticleSystem.spriteCellWidth;
            particleSystem.spriteCellHeight = parsedParticleSystem.spriteCellHeight;
            particleSystem.spriteCellChangeSpeed = parsedParticleSystem.spriteCellChangeSpeed;
        }

        /**
         * Parses a JSON object to create a particle system.
         * @param parsedParticleSystem The JSON object to parse
         * @param scene The scene to create the particle system in
         * @param rootUrl The root url to use to load external dependencies like texture
         * @returns the Parsed particle system
         */
        public static Parse(parsedParticleSystem: any, scene: Scene, rootUrl: string): ParticleSystem {
            var name = parsedParticleSystem.name;
            var custom: Nullable<Effect> = null;
            var program: any = null;
            if (parsedParticleSystem.customShader) {
                program = parsedParticleSystem.customShader;
                var defines: string = (program.shaderOptions.defines.length > 0) ? program.shaderOptions.defines.join("\n") : "";
                custom = scene.getEngine().createEffectForParticles(program.shaderPath.fragmentElement, program.shaderOptions.uniforms, program.shaderOptions.samplers, defines);
            }
            var particleSystem = new ParticleSystem(name, parsedParticleSystem.capacity, scene, custom, parsedParticleSystem.isAnimationSheetEnabled);
            particleSystem.customShader = program;

            if (parsedParticleSystem.id) {
                particleSystem.id = parsedParticleSystem.id;
            }

            // Auto start
            if (parsedParticleSystem.preventAutoStart) {
                particleSystem.preventAutoStart = parsedParticleSystem.preventAutoStart;
            }

            ParticleSystem._Parse(parsedParticleSystem, particleSystem, scene, rootUrl);

            particleSystem.textureMask = Color4.FromArray(parsedParticleSystem.textureMask);

            if (!particleSystem.preventAutoStart) {
                particleSystem.start();
            }

            return particleSystem;
        }
    }
}