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325 lines
5.9 KiB
325 lines
5.9 KiB
/*
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* Cloth Simulation using a relaxed constrains solver
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*/
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// Suggested Readings
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// Advanced Character Physics by Thomas Jakobsen Character
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// http://freespace.virgin.net/hugo.elias/models/m_cloth.htm
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// http://en.wikipedia.org/wiki/Cloth_modeling
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// http://cg.alexandra.dk/tag/spring-mass-system/
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// Real-time Cloth Animation http://www.darwin3d.com/gamedev/articles/col0599.pdf
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var DAMPING = 0.03;
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var DRAG = 1 - DAMPING;
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var MASS = .1;
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var restDistance = 25;
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var xSegs = 10; //
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var ySegs = 10; //
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var clothFunction = plane( restDistance * xSegs, restDistance * ySegs );
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var cloth = new Cloth( xSegs, ySegs );
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var GRAVITY = 981 * 1.4; //
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var gravity = new THREE.Vector3( 0, - GRAVITY, 0 ).multiplyScalar( MASS );
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var TIMESTEP = 18 / 1000;
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var TIMESTEP_SQ = TIMESTEP * TIMESTEP;
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var pins = [];
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var wind = true;
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var windStrength = 2;
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var windForce = new THREE.Vector3( 0, 0, 0 );
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var ballPosition = new THREE.Vector3( 0, - 45, 0 );
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var ballSize = 60; //40
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var tmpForce = new THREE.Vector3();
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var lastTime;
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function plane( width, height ) {
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return function( u, v ) {
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var x = ( u - 0.5 ) * width;
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var y = ( v + 0.5 ) * height;
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var z = 0;
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return new THREE.Vector3( x, y, z );
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};
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}
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function Particle( x, y, z, mass ) {
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this.position = clothFunction( x, y ); // position
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this.previous = clothFunction( x, y ); // previous
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this.original = clothFunction( x, y );
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this.a = new THREE.Vector3( 0, 0, 0 ); // acceleration
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this.mass = mass;
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this.invMass = 1 / mass;
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this.tmp = new THREE.Vector3();
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this.tmp2 = new THREE.Vector3();
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}
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// Force -> Acceleration
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Particle.prototype.addForce = function( force ) {
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this.a.add(
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this.tmp2.copy( force ).multiplyScalar( this.invMass )
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);
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};
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// Performs verlet integration
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Particle.prototype.integrate = function( timesq ) {
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var newPos = this.tmp.subVectors( this.position, this.previous );
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newPos.multiplyScalar( DRAG ).add( this.position );
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newPos.add( this.a.multiplyScalar( timesq ) );
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this.tmp = this.previous;
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this.previous = this.position;
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this.position = newPos;
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this.a.set( 0, 0, 0 );
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};
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var diff = new THREE.Vector3();
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function satisifyConstrains( p1, p2, distance ) {
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diff.subVectors( p2.position, p1.position );
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var currentDist = diff.length();
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if ( currentDist == 0 ) return; // prevents division by 0
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var correction = diff.multiplyScalar( 1 - distance / currentDist );
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var correctionHalf = correction.multiplyScalar( 0.5 );
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p1.position.add( correctionHalf );
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p2.position.sub( correctionHalf );
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}
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function Cloth( w, h ) {
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w = w || 10;
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h = h || 10;
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this.w = w;
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this.h = h;
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var particles = [];
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var constrains = [];
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var u, v;
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// Create particles
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for ( v = 0; v <= h; v ++ ) {
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for ( u = 0; u <= w; u ++ ) {
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particles.push(
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new Particle( u / w, v / h, 0, MASS )
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);
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}
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}
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// Structural
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for ( v = 0; v < h; v ++ ) {
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for ( u = 0; u < w; u ++ ) {
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constrains.push( [
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particles[ index( u, v ) ],
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particles[ index( u, v + 1 ) ],
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restDistance
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] );
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constrains.push( [
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particles[ index( u, v ) ],
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particles[ index( u + 1, v ) ],
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restDistance
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] );
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}
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}
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for ( u = w, v = 0; v < h; v ++ ) {
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constrains.push( [
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particles[ index( u, v ) ],
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particles[ index( u, v + 1 ) ],
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restDistance
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] );
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}
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for ( v = h, u = 0; u < w; u ++ ) {
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constrains.push( [
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particles[ index( u, v ) ],
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particles[ index( u + 1, v ) ],
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restDistance
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] );
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}
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// While many system uses shear and bend springs,
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// the relax constrains model seem to be just fine
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// using structural springs.
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// Shear
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// var diagonalDist = Math.sqrt(restDistance * restDistance * 2);
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// for (v=0;v<h;v++) {
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// for (u=0;u<w;u++) {
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// constrains.push([
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// particles[index(u, v)],
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// particles[index(u+1, v+1)],
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// diagonalDist
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// ]);
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// constrains.push([
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// particles[index(u+1, v)],
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// particles[index(u, v+1)],
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// diagonalDist
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// ]);
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// }
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// }
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this.particles = particles;
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this.constrains = constrains;
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function index( u, v ) {
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return u + v * ( w + 1 );
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}
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this.index = index;
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}
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function simulate( time ) {
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if ( ! lastTime ) {
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lastTime = time;
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return;
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}
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var i, il, particles, particle, pt, constrains, constrain;
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// Aerodynamics forces
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if ( wind ) {
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var face, faces = clothGeometry.faces, normal;
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particles = cloth.particles;
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for ( i = 0, il = faces.length; i < il; i ++ ) {
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face = faces[ i ];
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normal = face.normal;
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tmpForce.copy( normal ).normalize().multiplyScalar( normal.dot( windForce ) );
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particles[ face.a ].addForce( tmpForce );
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particles[ face.b ].addForce( tmpForce );
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particles[ face.c ].addForce( tmpForce );
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}
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}
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for ( particles = cloth.particles, i = 0, il = particles.length
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; i < il; i ++ ) {
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particle = particles[ i ];
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particle.addForce( gravity );
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particle.integrate( TIMESTEP_SQ );
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}
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// Start Constrains
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constrains = cloth.constrains,
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il = constrains.length;
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for ( i = 0; i < il; i ++ ) {
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constrain = constrains[ i ];
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satisifyConstrains( constrain[ 0 ], constrain[ 1 ], constrain[ 2 ] );
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}
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// Ball Constrains
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ballPosition.z = - Math.sin( Date.now() / 600 ) * 90 ; //+ 40;
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ballPosition.x = Math.cos( Date.now() / 400 ) * 70;
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if ( sphere.visible )
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for ( particles = cloth.particles, i = 0, il = particles.length
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; i < il; i ++ ) {
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particle = particles[ i ];
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pos = particle.position;
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diff.subVectors( pos, ballPosition );
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if ( diff.length() < ballSize ) {
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// collided
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diff.normalize().multiplyScalar( ballSize );
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pos.copy( ballPosition ).add( diff );
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}
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}
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// Floor Constains
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for ( particles = cloth.particles, i = 0, il = particles.length
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; i < il; i ++ ) {
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particle = particles[ i ];
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pos = particle.position;
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if ( pos.y < - 250 ) {
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pos.y = - 250;
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}
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}
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// Pin Constrains
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for ( i = 0, il = pins.length; i < il; i ++ ) {
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var xy = pins[ i ];
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var p = particles[ xy ];
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p.position.copy( p.original );
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p.previous.copy( p.original );
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}
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}
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