同一种用法

sim.tire(new Vec2(200,50), 50, 30, 0.3, 0.9);

官方实现

VerletJS.prototype.tire = function(origin, radius, segments, spokeStiffness, treadStiffness) {
    var stride = (2*Math.PI)/segments;
    var i;

    var composite = new this.Composite();

    // particles
    for (i=0;i<segments;++i) {
        var theta = i*stride;
        composite.particles.push(new Particle(new Vec2(origin.x + Math.cos(theta)*radius, origin.y + Math.sin(theta)*radius)));
    }

    var center = new Particle(origin);
    composite.particles.push(center);

    // constraints
    for (i=0;i<segments;++i) {
        composite.constraints.push(new DistanceConstraint(composite.particles[i], composite.particles[(i+1)%segments], treadStiffness));
        composite.constraints.push(new DistanceConstraint(composite.particles[i], center, spokeStiffness))
        composite.constraints.push(new DistanceConstraint(composite.particles[i], composite.particles[(i+5)%segments], treadStiffness));
    }

    this.composites.push(composite);
    return composite;
}

用上 AngleConstraint

VerletJS.prototype.tire = function(origin, radius, segments, spokeStiffness, treadStiffness) {
            var stride = (2*Math.PI)/segments;
            var i;

            var composite = new this.Composite();

            // particles
            for (i=0;i<segments;++i) {
                var theta = i*stride;
                composite.particles.push(new Particle(new Vec2(origin.x + Math.cos(theta)*radius, origin.y + Math.sin(theta)*radius)));
            }

            // constraints
            for (i=0;i<segments;++i) {
                composite.constraints.push(new DistanceConstraint(composite.particles[i], composite.particles[(i+1)%segments], treadStiffness));
                composite.constraints.push(new AngleConstraint(composite.particles[i], composite.particles[(i+1)%segments], composite.particles[(i+2)%segments], treadStiffness));
            }

            this.composites.push(composite);
            return composite;
        }