联系与渊源

在 verlet-js 中，pin 住一点是复合材料的一个通用方法

verlet.js 部分源码

Composite.prototype.pin = function(index, pos) {
    pos = pos || this.particles[index].pos;
    var pc = new PinConstraint(this.particles[index], pos);
    this.constraints.push(pc);
    return pc;
}

更方便的使用

shapes.html 部分源码

var segment = sim.lineSegments([new Vec2(20,10), new Vec2(40,10), new Vec2(60,10), new Vec2(80,10), new Vec2(100,10)], 0.02);
        var pin = segment.pin(0);
        var pin = segment.pin(4);

lineSegments 的实体原型中就没必要提供（重写） pin 方法了

原型定义时也可以这样用

objects.js 部分源码

VerletJS.prototype.cloth = function(origin, width, height, segments, pinMod, stiffness) {

    var composite = new this.Composite();

    var xStride = width/segments;
    var yStride = height/segments;

    var x,y;
    for (y=0;y<segments;++y) {
        for (x=0;x<segments;++x) {
            var px = origin.x + x*xStride - width/2 + xStride/2;
            var py = origin.y + y*yStride - height/2 + yStride/2;
            composite.particles.push(new Particle(new Vec2(px, py)));

            if (x > 0)
                composite.constraints.push(new DistanceConstraint(composite.particles[y*segments+x], composite.particles[y*segments+x-1], stiffness));

            if (y > 0)
                composite.constraints.push(new DistanceConstraint(composite.particles[y*segments+x], composite.particles[(y-1)*segments+x], stiffness));
        }
    }

    for (x=0;x<segments;++x) {
        if (x%pinMod == 0)
        composite.pin(x);  //看这里，看这里，看这里啊啊啊啊
    }

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