html-canvas背景设置

将canvas设置为背景

Posted by Kingtous on May 4, 2019

在canvas中加入style

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style="position:fixed;top:0;left:0;z-index:-1"

说明

  • position:fixed,固定canvas,使得画布固定在视图中,不会滚动
  • top,left表明从左上角开始(此设置与canvas有关,不一定)
  • z-index:-1,将canvas置于底层

例子(网站使用的粒子特效)

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<canvas id="Mycanvas" style="position:fixed;top:0;left:0;z-index:-1"></canvas>
    <script>
        //定义画布宽高和生成点的个数
        var WIDTH = window.innerWidth, HEIGHT = window.innerHeight, POINT = 8;
        var canvas = document.getElementById('Mycanvas');
        canvas.width = WIDTH,
        canvas.height = HEIGHT;
        var context = canvas.getContext('2d');
        context.strokeStyle = 'rgba(0,0,0,0.2)',
        context.strokeWidth = 1,
        context.fillStyle = 'rgba(0,0,0,0.1)';
        var circleArr = [];

        //线条:开始xy坐标,结束xy坐标,线条透明度
        function Line (x, y, _x, _y, o) {
            this.beginX = x,
            this.beginY = y,
            this.closeX = _x,
            this.closeY = _y,
            this.o = o;
        }
        //点:圆心xy坐标,半径,每帧移动xy的距离
        function Circle (x, y, r, moveX, moveY) {
            this.x = x,
            this.y = y,
            this.r = r,
            this.moveX = moveX,
            this.moveY = moveY;
        }
        //生成max和min之间的随机数
        function num (max, _min) {
            var min = arguments[1] || 0;
            return Math.floor(Math.random()*(max-min+1)+min);
        }
        // 绘制原点
        function drawCricle (cxt, x, y, r, moveX, moveY) {
            var circle = new Circle(x, y, r, moveX, moveY)
            cxt.beginPath()
            cxt.arc(circle.x, circle.y, circle.r, 0, 2*Math.PI)
            cxt.closePath()
            cxt.fill();
            return circle;
        }
        //绘制线条
        function drawLine (cxt, x, y, _x, _y, o) {
            var line = new Line(x, y, _x, _y, o)
            cxt.beginPath()
            cxt.strokeStyle = 'rgba(0,0,0,'+ o +')'
            cxt.moveTo(line.beginX, line.beginY)
            cxt.lineTo(line.closeX, line.closeY)
            cxt.closePath()
            cxt.stroke();

        }
        //初始化生成原点
        function init () {
            circleArr = [];
            for (var i = 0; i < POINT; i++) {
                circleArr.push(drawCricle(context, num(WIDTH), num(HEIGHT), num(15, 2), num(10, -10)/40, num(10, -10)/40));
            }
            draw();
        }

        //每帧绘制
        function draw () {
            context.clearRect(0,0,canvas.width, canvas.height);
            for (var i = 0; i < POINT; i++) {
                drawCricle(context, circleArr[i].x, circleArr[i].y, circleArr[i].r);
            }
            for (var i = 0; i < POINT; i++) {
                for (var j = 0; j < POINT; j++) {
                    if (i + j < POINT) {
                        var A = Math.abs(circleArr[i+j].x - circleArr[i].x),
                            B = Math.abs(circleArr[i+j].y - circleArr[i].y);
                        var lineLength = Math.sqrt(A*A + B*B);
                        var C = 1/lineLength*7-0.009;
                        var lineOpacity = C > 0.03 ? 0.03 : C;
                        if (lineOpacity > 0) {
                            drawLine(context, circleArr[i].x, circleArr[i].y, circleArr[i+j].x, circleArr[i+j].y, lineOpacity);
                        }
                    }
                }
            }
        }

        //调用执行
        window.onload = function () {
            init();
            setInterval(function () {
                for (var i = 0; i < POINT; i++) {
                    var cir = circleArr[i];
                    cir.x += cir.moveX;
                    cir.y += cir.moveY;
                    if (cir.x > WIDTH) cir.x = 0;
                    else if (cir.x < 0) cir.x = WIDTH;
                    if (cir.y > HEIGHT) cir.y = 0;
                    else if (cir.y < 0) cir.y = HEIGHT;
                    
                }
                draw();
            }, 16);
        }
    </script>