1.1 预期效果

大屏场景下，给决策报表添加一个酷炫的大屏旋转星空背景，如下图所示：

1.2 实现思路

用户可直接用 JS 代码来制作旋转的动态星空背景。

2.1 新建报表

新建决策报表，另存为：%FR_HOME%\webapps\webroot\WEB-INF\reportlets\doc\JS\表单JS实例\33-JS实现大屏旋转星空背景.frm。

2.2 添加初始化后事件

注：需先将 body 背景设置为「自定义>没有背景」。

点击 body 组件，添加初始化后事件，如下图所示：

JavaScript 代码如下：

revolveStars();function revolveStars(){
$("body").prepend('<canvas id="canvas" style="position:absolute;z-index:-2;"></canvas>');
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 = 1100;                //星星数量,默认1300
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, '#CCC');
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();
// End cache
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;
}
function maxOrbit(x, y) {
    var max = Math.max(x, y),
    diameter = Math.round(Math.sqrt(max * max + max * max));
    return diameter / 2;
    //星星移动范围，值越大范围越小，
}
var Star = function() {
    this.orbitRadius = random(maxOrbit(w, h));
    this.radius = random(60, this.orbitRadius) / 10;       //星星大小,值越大星星越小,默认8
    
    this.orbitX = w / 2;
    this.orbitY = h / 2;
    this.timePassed = random(0, maxStars);
    this.speed = random(this.orbitRadius) / 80000;        //星星移动速度,值越大越慢,默认5W
    
    this.alpha = random(2, 10) / 10;
    count++;
    stars[count] = this;
}
Star.prototype.draw = function() {
    var x = Math.sin(this.timePassed) * this.orbitRadius + this.orbitX,
    y = Math.cos(this.timePassed) * this.orbitRadius + 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 = 0.5;                                 //尾巴
    ctx.fillStyle = 'hsla(' + hue + ', 64%, 6%, 2)';
    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(); 
window.onresize = function(){revolveStars();}}

2.3 效果预览

保存模板，点击「PC端预览」，效果如 1.1 预期效果所示。

注：不支持移动端。

点击下载模板：JS实现大屏旋转星空背景.frm