JavaScript实现背景随机线条效果

效果展示

代码

<canvas id="cas"></canvas>
<script>
        var canvas = document.getElementById("cas");
        var ctx = canvas.getContext("2d");
        resize();
        window.onresize = resize;
        function resize() {
            canvas.width = window.innerWidth || document.documentElement.clientWidth || document.body.clientWidth;
            canvas.height = window.innerHeight || document.documentElement.clientHeight || document.body.clientHeight;
        }
        var RAF = (function () {
            return window.requestAnimationFrame || window.webkitRequestAnimationFrame || window.mozRequestAnimationFrame || window.oRequestAnimationFrame || window.msRequestAnimationFrame || function (callback) {
                window.setTimeout(callback, 1000 / 60);
            };
        })();
        // 鼠标活动时，获取鼠标坐标
        var warea = { x: null, y: null, max: 20000 };
        window.onmousemove = function (e) {
            e = e || window.event;
            warea.x = e.clientX;
            warea.y = e.clientY;
        };
        window.onmouseout = function (e) {
            warea.x = null;
            warea.y = null;
        };
        // 添加粒子
        // x，y为粒子坐标，xa, ya为粒子xy轴加速度，max为连线的最大距离
        var dots = [];
        for (var i = 0; i < 300; i++) {
            var x = Math.random() * canvas.width;
            var y = Math.random() * canvas.height;
            var xa = Math.random() * 2 - 1;
            var ya = Math.random() * 2 - 1;
            dots.push({
                x: x,
                y: y,
                xa: xa,
                ya: ya,
                max: 6000
            })
        }
        // 延迟100秒开始执行动画，如果立即执行有时位置计算会出错
        setTimeout(function () {
            animate();
        }, 100);
        // 每一帧循环的逻辑
        function animate() {
            ctx.clearRect(0, 0, canvas.width, canvas.height);
            // 将鼠标坐标添加进去，产生一个用于比对距离的点数组
            var ndots = [warea].concat(dots);
            dots.forEach(function (dot) {
                // 粒子位移
                dot.x += dot.xa;
                dot.y += dot.ya;
                // 遇到边界将加速度反向
                dot.xa *= (dot.x > canvas.width || dot.x < 0) ? -1 : 1;
                dot.ya *= (dot.y > canvas.height || dot.y < 0) ? -1 : 1;
                // 绘制点
                ctx.fillRect(dot.x - 0.5, dot.y - 0.5, 1, 1);
                // 循环比对粒子间的距离
                for (var i = 0; i < ndots.length; i++) {
                    var d2 = ndots[i];
                    if (dot === d2 || d2.x === null || d2.y === null) continue;
                    var xc = dot.x - d2.x;
                    var yc = dot.y - d2.y;
                    // 两个粒子之间的距离
                    var dis = xc * xc + yc * yc;
                    // 距离比
                    var ratio;
                    // 如果两个粒子之间的距离小于粒子对象的max值，则在两个粒子间画线
                    if (dis < d2.max) {
                        // 如果是鼠标，则让粒子向鼠标的位置移动
                        if (d2 === warea && dis > (d2.max / 2)) {
                            dot.x -= xc * 0.03;
                            dot.y -= yc * 0.03;
                        }
                        // 计算距离比
                        ratio = (d2.max - dis) / d2.max;
                        // 画线
                        ctx.beginPath();
                        ctx.lineWidth = ratio / 2;
                        ctx.strokeStyle = 'rgba(0,0,0,' + (ratio + 0.2) + ')';
                        ctx.moveTo(dot.x, dot.y);
                        ctx.lineTo(d2.x, d2.y);
                        ctx.stroke();
                    }
                }
                // 将已经计算过的粒子从数组中删除
                ndots.splice(ndots.indexOf(dot), 1);
            });
            RAF(animate);
        }
    </script>