canvas画小蝌蚪模拟气象风场

<style type="text/css">
    canvas {
        margin: 20px;
    }
</style>

<h1>小蝌蚪模拟风场</h1>
<canvas id="canvas" width=700 height=500 style="border: 1px solid #ccc;"></canvas>

<script>
    $(function () {
        var Arrow = function (x, y, angle, speed, alive) {
            this.x = x;
            this.y = y;
            this.angle = angle;
            this.speed = speed || 10; //小蝌蚪长度来代表速度
            this.alive = alive || true; //是否活着
            this.liveLength = Math.random() * 20; //生命长度
        };

        self.init = function () {
            this.canvas = document.getElementById(‘canvas‘);
            this.ctx = canvas.getContext(‘2d‘);
            this.cw = this.canvas.width;
            this.ch = this.canvas.height;
            this.arrows = this.initArrows();
        };

        self.initArrows = function () {
            var count = 200, arrowArray = [], arrow = {};
            while (count--) {
                arrow = new Arrow(Math.random() * this.cw, Math.random() * this.ch, Math.random() * 360, 10, true);
                arrowArray.push(arrow);
            }
            return arrowArray;
        };

        self.createArrows = function () {
            this.ctx.clearRect(0, 0, this.cw, this.ch);
            var i = this.arrows.length;
            while (i--) {
                var arrow = this.arrows[i];
                arrow.reset();
                if (arrow.alive) {
                    arrow.draw();
                } else {
                    arrow.relive();
                }
            }
        };

        Arrow.prototype.draw = function () {
            var ex = ey = 0;
            ex = this.x - this.speed * Math.sin((180 - this.angle) * (Math.PI / 180)); //↓0°←90°
            ey = this.y - this.speed * Math.cos((180 - this.angle) * (Math.PI / 180));
            ctx.beginPath();
            ctx.translate(0, 0, 0); //坐标源点
            ctx.moveTo(this.x, this.y);
            ctx.lineTo(ex, ey);
            ctx.fill();
            ctx.stroke();
            ctx.save();

            ctx.translate(ex, ey);
            //我的箭头本垂直向下，算出直线偏离Y的角，然后旋转 ,rotate是顺时针旋转的，所以加个负号
            var ang = (ex - this.x) / (ey - this.y);
            ang = Math.atan(ang);
            ey - this.y >= 0 ? ctx.rotate(-ang) : ctx.rotate(Math.PI - ang);//加个180度，反过来
            ctx.lineTo(-4, -4);
            ctx.lineTo(0, -4);
            ctx.lineTo(4, -4);
            ctx.lineTo(0, 0);
            ctx.fill(); //箭头是个封闭图形
            ctx.restore(); //用来恢复Canvas之前保存的状态,否则会影响后续绘制
            ctx.closePath();

            this.x = ex; //终点当起点
            this.y = ey;
        };

        Arrow.prototype.reset = function () {
            this.liveLength--;
            if (this.liveLength <= 0) {
                this.alive = false;
            }
            if (this.x < 0 || this.y < 0 || this.x > self.cw || this.y > self.ch) {
                this.alive = false;
            }
        };

        Arrow.prototype.relive = function () {
            this.alive = true;
            this.x = Math.random() * self.cw;
            this.y = Math.random() * self.ch;
            this.liveLength = Math.random() * 20;
        };

        self.init();

        var animateArrow = function () {
            self.createArrows();
        };

        var timer = setInterval(animateArrow, 200);
    });
</script>