source: other-projects/nz-flag-design/trunk/render-3d/weather/snow.js@ 29620

    function snow() {
    
        this.isInit = false;
        this.Mass = 0.01;
        
        this.init = function() {
            
            // modify lighting
            this.HSL = light.color.getHSL();
            light.color.setHSL(this.HSL.h, this.HSL.s, 0.6);
        
            if(this.isInit === true) return;
        
            // create the particle variables
            this.particleCount = 2000,
            this.particles = new THREE.Geometry(),
            
            this.pMaterial = new THREE.ParticleBasicMaterial({
                color: 0xFFFFFF,
                size: 25,
                map: THREE.ImageUtils.loadTexture(
                    "./images/snow.png"
                ),
                blending: THREE.AdditiveBlending,
                transparent: true,
                opacity: 0.9
            });

            // now create the individual particles
            for (var p = 0; p < this.particleCount; p++) {

                // create a particle with random
                // position values, -250 -> 250
                var pX = Math.random() * window.innerWidth * 3 - window.innerWidth,
                    pY = Math.random() * window.innerHeight * 4 - window.innerHeight,
                    pZ = Math.random() * window.innerWidth * 3 - window.innerWidth;
                    this.particle = new THREE.Vector3(pX, pY, pZ);  
                
                // create a velocity vector
                this.particle.velocity = new THREE.Vector3(
                    0, // x
                    -Math.random(), // y
                    0); // z

                // add it to the geometry
                this.particles.vertices.push(this.particle);
            
            }
            
            // create the particle system
            this.particleSystem = new THREE.ParticleSystem(
                this.particles,
                this.pMaterial);

            this.particleSystem.sortParticles = true;
            
            this.isInit = true;
        }
    
        this.system = function(){
            return this.particleSystem;
        }
    
        this.update = function() {
            // add some rotation to the system
            //particleSystem.rotation.y += 0.01;
            
            var pCount = this.particleCount;
            while(pCount--) {
                // get the particle
                this.particle = this.particles.vertices[pCount];
                
                // check if we need to reset
                if(this.particle.y < -200) {
                    this.particle.y = Math.random() * window.innerHeight+10;
                    this.particle.velocity.y = 0;
                }
                
                // update the velocity
                this.particle.velocity.y -= Math.random() * this.Mass;
                
                // and the position
                this.particle.addVectors( 
                    this.particle,
                    this.particle.velocity);
            }
        
            // flag to the particle system that we've
            // changed its vertices.
            this.particleSystem.geometry.__dirtyVertices = true;
        }
}