JS实现大屏旋转星空背景

  • 文档创建者:星踪
  • 编辑次数:8次
  • 最近更新:Leo.Tsai 于 2020-03-26
  • 1. 概述

    1.1 应用场景

    大屏场景下给决策报表添加一个酷炫的旋转星空效果。

    旋转星空.gif

    1.2 实现思路

    采用插入动态 GIF 背景图的方式是无法进行自适应的,所以直接用 JS 代码来制作效果更好。

    2. 示例

    FineReport.frm为例,给 body 组件添加一个初始化后事件,JS 代码如下:

    function background() {
    $("body").prepend('<canvas id="canvas" style="position:absolute;z-index:-2;"></canvas>');
    //在body中插入canvas画布,并置于底层
    var canvas = document.getElementById('canvas'),
    ctx = canvas.getContext('2d'),
    w = canvas.width = window.innerWidth,
    h = canvas.height = window.innerHeight,

    hue = 217,
    stars = [],
    count = 0,
    maxStars = 800;
    //设置星星数量

    var canvas2 = document.createElement('canvas'),
    ctx2 = canvas2.getContext('2d');
    canvas2.width = 100;
    canvas2.height = 100;
    var half = canvas2.width / 2,
    gradient2 = ctx2.createRadialGradient(half, half, 0, half, half, half);
    gradient2.addColorStop(0.025, '#fff');
    gradient2.addColorStop(0.1, 'hsl(' + hue + ', 61%, 33%)');
    gradient2.addColorStop(0.25, 'hsl(' + hue + ', 64%, 6%)');
    gradient2.addColorStop(1, 'transparent');

    ctx2.fillStyle = gradient2;
    ctx2.beginPath();
    ctx2.arc(half, half, half, 0, Math.PI * 2);
    ctx2.fill();

    function random(min, max) {
    if (arguments.length < 2) {
    max = min;
    min = 0;
    }

    if (min > max) {
    var hold = max;
    max = min;
    min = hold;
    }

    return Math.floor(Math.random() * (max - min + 1)) + min;
    }

    var Star = function() {

    this.orbitRadius = random(w / 2 - 50);
    this.radius = random(100, this.orbitRadius) / 10;
    this.orbitX = w / 2;
    this.orbitY = h / 2;
    this.timePassed = random(0, maxStars);
    this.speed = random(this.orbitRadius) / 500000;
    //设置旋转速度
    this.alpha = random(2, 10) / 10;

    count++;
    stars[count] = this;
    }

    Star.prototype.draw = function() {
    var x = Math.sin(this.timePassed + 1) * this.orbitRadius + this.orbitX,
    y = Math.cos(this.timePassed) * this.orbitRadius / 2 + this.orbitY,
    twinkle = random(10);

    if (twinkle === 1 && this.alpha > 0) {
    this.alpha -= 0.05;
    } else if (twinkle === 2 && this.alpha < 1) {
    this.alpha += 0.05;
    }

    ctx.globalAlpha = this.alpha;
    ctx.drawImage(canvas2, x - this.radius / 2, y - this.radius / 2, this.radius, this.radius);
    this.timePassed += this.speed;
    }

    for (var i = 0; i < maxStars; i++) {
    new Star();
    }

    function animation() {
    ctx.globalCompositeOperation = 'source-over';
    ctx.globalAlpha = 0.8;
    ctx.fillStyle = 'hsla(' + hue + ', 64%, 6%, 1)';
    ctx.fillRect(0, 0, w, h)

    ctx.globalCompositeOperation = 'lighter';
    for (var i = 1, l = stars.length; i < l; i++) {
    stars[i].draw();
    };

    window.requestAnimationFrame(animation);
    }
    animation();
    }
    background();
    $(window).resize(function() {
    background();
    })

    3. 效果预览

    保存决策报表,点击表单预览,效果图如应用场景中所示。

    注:不支持移动端。

    4. 已完成模板

    已完成模板可参见:%FR_HOME%\webapps\webroot\WEB-INF\reportlets\doc\JS\表单JS实例\大屏旋转星空背景图.frm

    点击下载模板:大屏旋转星空背景图.frm

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