source: other-projects/nz-flag-design/trunk/render-3d/Flag_files/rain.js@ 29475

var particleCount;
var particleSystem;

function rain(){    
    // create the particle variables
        particleCount = 3600,
        particles = new THREE.Geometry(),
        pMaterial = new THREE.ParticleBasicMaterial({
            color: 0xFFFFFF,
            size: 10,
            map: THREE.ImageUtils.loadTexture(
                "./images/raindrop.png"
            ),
            blending: THREE.AdditiveBlending,
            transparent: true,
            opacity: 0.5
        });
    
    // now create the individual particles
    for(var p = 0; p < particleCount; p++) {
    
        // create a particle with random
        // position values, -250 -> 250
        var pX = Math.random() * window.innerWidth*2 - window.innerWidth,
            pY = Math.random() * window.innerHeight*3 - window.innerHeight,
            pZ = Math.random() * window.innerWidth*2 - window.innerWidth,
            particle = new THREE.Vector3(pX, pY, pZ)
                
        // create a velocity vector
        particle.velocity = new THREE.Vector3(
            0,              // x
            -Math.random(), // y
            0);             // z

        // add it to the geometry
        particles.vertices.push(particle);
    }
    
    // create the particle system
        particleSystem = new THREE.ParticleSystem(
        particles,
        pMaterial);
    
    particleSystem.sortParticles = true;
    
    return particleSystem;
}
    // animation loop
    function updateRain() {
        
        // add some rotation to the system
        particleSystem.rotation.y += 0.001;
        
        var pCount = particleCount;
        while(pCount--) {
            // get the particle
            var particle = particles.vertices[pCount];
            
            // check if we need to reset
            if(particle.y < -200) {
                particle.y = 200;
                particle.velocity.y = 0;
            }
            
            // update the velocity
            particle.velocity.y -= Math.random() * .1;
            
            // and the position
            particle.addVectors( 
                particle,
                particle.velocity);
        }
        
        // flag to the particle system that we've
        // changed its vertices. This is the
        // dirty little secret.
        particleSystem.geometry.__dirtyVertices = true;
        
    }