canvas做动画时,切到其他tab再切回来,中间的动画没有执行。直接从切出时跳到了切回来的状态。

明非
  • 656

这是正常运行,会画一个圆。
clipboard.png

如果我中途切出tab在回来。就会变成这样了

clipboard.png

<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <title>aaa</title>
 
</head>

<body>
    <canvas id="demoCanvas" width="500" height="700"></canvas>
    <script>
    var canvas = demoCanvas;
    var ctx = canvas.getContext('2d');
    var startTime = Date.now();
    var duration = 11100;
    var r = 100;

    requestAnimationFrame(animate)


    var p = Math.min(1.0, (Date.now() - startTime) / duration);
    var tx = r * Math.sin(2 * Math.PI * p) + 200,
        ty = -r * Math.cos(2 * Math.PI * p) + 200;
    ctx.fillStyle = 'green';
    ctx.beginPath();
    ctx.moveTo(tx, ty);


    function animate() {
        // ctx.clearRect(0,0,1000,1000);

        var p = Math.min(1.0, (Date.now() - startTime) / duration);
        var tx = r * Math.sin(2 * Math.PI * p) + 200,
            ty = -r * Math.cos(2 * Math.PI * p) + 200;

        ctx.lineTo(tx, ty);
            ctx.stroke();

        if (p < 1.0) requestAnimationFrame(animate)
    }
    </script>
</body>

</html>
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2 个回答
明非
  • 656
✓ 已被采纳

一年过去了,还是自己回来解决自己提出的问题吧。可能是一开始没有描述清楚问题,没有人来回答我。哈哈

是这样的,为了性能和电量,RequestAnimationFrame 在页面后台运行或者不可见的<iframe>里面会降低帧率,从这个情形看,chrome浏览器中,页面后台运行时,回调函数是不被调用的。

从上面代码可以看出,我所画的点是根据时间来计算出来的位置,我用了当前时间减去了开始时间,这样的话,离开页面以后当前时间也是会走的,但RequestAnimationFrame并不工作,所以中间的点自然被忽略了,我们要保持时间的连续性,所以可以记录离开页面的时间,每次计算的时候,用当前时间减去开始时间再减去离开的时间,算出真正在页面中,也就是RequestAnimationFrame正常工作的时间,当然,使用这种方式,离开页面的时候画圆过程也将会被停止,回来以后继续画。

代码如下:

<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <title>aaa</title>
 
</head>

<body>
    <canvas id="demoCanvas" width="500" height="700"></canvas>
    <script>
    var canvas = demoCanvas;
    var ctx = canvas.getContext('2d');
    var startTime = Date.now();
    var duration = 11100;
    var r = 100;
    
    let leaveTime;
    let allLeaveTime = 0;

    requestAnimationFrame(animate)


    var p = Math.min(1.0, (Date.now() - startTime) / duration);
    var tx = r * Math.sin(2 * Math.PI * p) + 200,
        ty = -r * Math.cos(2 * Math.PI * p) + 200;
    ctx.fillStyle = 'green';
    ctx.beginPath();
    ctx.moveTo(tx, ty);


    function animate() {
        // ctx.clearRect(0,0,1000,1000);

        var p = Math.min(1.0, (Date.now() - allLeaveTime - startTime) / duration);
        var tx = r * Math.sin(2 * Math.PI * p) + 200,
            ty = -r * Math.cos(2 * Math.PI * p) + 200;

        ctx.lineTo(tx, ty);
            ctx.stroke();

        if (p < 1.0) requestAnimationFrame(animate)
    }


    document.addEventListener('visibilitychange', function (e) {
        if (e.target.hidden) {
            leaveTime = Date.now();
        } else {
            allLeaveTime += (Date.now() - leaveTime);
        }
    })
    </script>
</body>

</html>
但磊
  • 2
新手上路,请多包涵

我也遇到这个问题,但是找不到解决方法,你能帮我看看吗

<!DOCTYPE html>
<html>
<head>
    <meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
    <title>html5实现鼠标点击烟花播放效果</title>

    <style>
        html, body {
            height: 100%;
            margin: 0;
            padding: 0
        }

        ul, li {
            text-indent: 0;
            text-decoration: none;
            margin: 0;
            padding: 0
        }

        img {
            border: 0
        }

        body {
            background-color: #000;
            color: #999;
            font: 100%/18px helvetica, arial, sans-serif
        }

        canvas {
            cursor: crosshair;
            display: block;
            left: 0;
            position: absolute;
            top: 0;
            z-index: 20
        }
    </style>

</head>
<body>

<script type="text/javascript"
        src="http://www.17sucai.com/preview/119710/2015-02-09/%E6%96%B0%E5%BB%BA%E6%96%87%E4%BB%B6%E5%A4%B9/js/jquery-2.0.0.min.js"></script>
<script type="text/javascript">
    $(function () {
        var Fireworks = function () {
            var self = this;
            var rand = function (rMi, rMa) {
                return ~~((Math.random() * (rMa - rMi + 1)) + rMi);
            }
            var hitTest = function (x1, y1, w1, h1, x2, y2, w2, h2) {
                return !(x1 + w1 < x2 || x2 + w2 < x1 || y1 + h1 < y2 || y2 + h2 < y1);
            };
            window.requestAnimFrame = function () {
                return window.requestAnimationFrame || window.webkitRequestAnimationFrame || window.mozRequestAnimationFrame || window.oRequestAnimationFrame || window.msRequestAnimationFrame || function (a) {
                        window.setTimeout(a, 1E3 / 60)
                    }
            }();

            self.init = function () {
                self.canvas = document.createElement('canvas');
                self.canvas.width = self.cw = $(window).innerWidth();
                self.canvas.height = self.ch = $(window).innerHeight();
                self.particles = [];
                self.partCount = 150;
                self.fireworks = [];
                self.mx = self.cw / 2;
                self.my = self.ch / 2;
                self.currentHue = 30;
                self.partSpeed = 5;
                self.partSpeedVariance = 10;
                self.partWind = 50;
                self.partFriction = 5;
                self.partGravity = 1;
                self.hueMin = 0;
                self.hueMax = 360;
                self.fworkSpeed = 0.1;
                self.fworkAccel = 10;
                self.hueVariance = 30;
                self.flickerDensity = 25;
                self.showShockwave = true;
                self.showTarget = false;
                self.clearAlpha = 25;

                $(document.body).append(self.canvas);
                self.ctx = self.canvas.getContext('2d');
                self.ctx.lineCap = 'round';
                self.ctx.lineJoin = 'round';
                self.lineWidth = 1;
                self.bindEvents();
                self.canvasLoop();

                self.canvas.onselectstart = function () {
                    return false;
                };
            };

            self.createParticles = function (x, y, hue) {
                var countdown = self.partCount;
                while (countdown--) {
                    var newParticle = {
                        x: x,
                        y: y,
                        coordLast: [
                            {x: x, y: y},
                            {x: x, y: y},
                            {x: x, y: y}
                        ],
                        angle: rand(0, 360),
                        speed: rand(((self.partSpeed - self.partSpeedVariance) <= 0) ? 1 : self.partSpeed - self.partSpeedVariance, (self.partSpeed + self.partSpeedVariance)),
                        friction: 1 - self.partFriction / 100,
                        gravity: self.partGravity / 2,
                        hue: rand(hue - self.hueVariance, hue + self.hueVariance),
                        brightness: rand(50, 80),
                        alpha: rand(40, 100) / 100,
                        decay: rand(10, 50) / 1000,
                        wind: (rand(0, self.partWind) - (self.partWind / 2)) / 25,
                        lineWidth: self.lineWidth
                    };
                    self.particles.push(newParticle);
                }
            };


            self.updateParticles = function () {
                var i = self.particles.length;
                while (i--) {
                    var p = self.particles[i];
                    var radians = p.angle * Math.PI / 180;
                    var vx = Math.cos(radians) * p.speed;
                    var vy = Math.sin(radians) * p.speed;
                    p.speed *= p.friction;

                    p.coordLast[2].x = p.coordLast[1].x;
                    p.coordLast[2].y = p.coordLast[1].y;
                    p.coordLast[1].x = p.coordLast[0].x;
                    p.coordLast[1].y = p.coordLast[0].y;
                    p.coordLast[0].x = p.x;
                    p.coordLast[0].y = p.y;

                    p.x += vx;
                    p.y += vy;
                    p.y += p.gravity;

                    p.angle += p.wind;
                    p.alpha -= p.decay;

                    if (!hitTest(0, 0, self.cw, self.ch, p.x - p.radius, p.y - p.radius, p.radius * 2, p.radius * 2) || p.alpha < .05) {
                        self.particles.splice(i, 1);
                    }
                }
                ;
            };

            self.drawParticles = function () {
                var i = self.particles.length;
                while (i--) {
                    var p = self.particles[i];

                    var coordRand = (rand(1, 3) - 1);
                    self.ctx.beginPath();
                    self.ctx.moveTo(Math.round(p.coordLast[coordRand].x), Math.round(p.coordLast[coordRand].y));
                    self.ctx.lineTo(Math.round(p.x), Math.round(p.y));
                    self.ctx.closePath();
                    self.ctx.strokeStyle = 'hsla(' + p.hue + ', 100%, ' + p.brightness + '%, ' + p.alpha + ')';
                    self.ctx.stroke();

                    if (self.flickerDensity > 0) {
                        var inverseDensity = 50 - self.flickerDensity;
                        if (rand(0, inverseDensity) === inverseDensity) {
                            self.ctx.beginPath();
                            self.ctx.arc(Math.round(p.x), Math.round(p.y), rand(p.lineWidth, p.lineWidth + 3) / 2, 0, Math.PI * 2, false)
                            self.ctx.closePath();
                            var randAlpha = rand(50, 100) / 100;
                            self.ctx.fillStyle = 'hsla(' + p.hue + ', 100%, ' + p.brightness + '%, ' + randAlpha + ')';
                            self.ctx.fill();
                        }
                    }
                }
                ;
            };


            self.createFireworks = function (startX, startY, targetX, targetY) {
                var newFirework = {
                    x: startX,
                    y: startY,
                    startX: startX,
                    startY: startY,
                    hitX: false,
                    hitY: false,
                    coordLast: [
                        {x: startX, y: startY},
                        {x: startX, y: startY},
                        {x: startX, y: startY}
                    ],
                    targetX: targetX,
                    targetY: targetY,
                    speed: self.fworkSpeed,
                    angle: Math.atan2(targetY - startY, targetX - startX),
                    shockwaveAngle: Math.atan2(targetY - startY, targetX - startX) + (90 * (Math.PI / 180)),
                    acceleration: self.fworkAccel / 100,
                    hue: self.currentHue,
                    brightness: rand(50, 80),
                    alpha: rand(50, 100) / 100,
                    lineWidth: self.lineWidth
                };
                self.fireworks.push(newFirework);

            };


            self.updateFireworks = function () {
                var i = self.fireworks.length;

                while (i--) {
                    var f = self.fireworks[i];
                    self.ctx.lineWidth = f.lineWidth;

                    vx = Math.cos(f.angle) * f.speed,
                        vy = Math.sin(f.angle) * f.speed;
                    f.speed *= 1 + f.acceleration;
                    f.coordLast[2].x = f.coordLast[1].x;
                    f.coordLast[2].y = f.coordLast[1].y;
                    f.coordLast[1].x = f.coordLast[0].x;
                    f.coordLast[1].y = f.coordLast[0].y;
                    f.coordLast[0].x = f.x;
                    f.coordLast[0].y = f.y;

                    if (f.startX >= f.targetX) {
                        if (f.x + vx <= f.targetX) {
                            f.x = f.targetX;
                            f.hitX = true;
                        } else {
                            f.x += vx;
                        }
                    } else {
                        if (f.x + vx >= f.targetX) {
                            f.x = f.targetX;
                            f.hitX = true;
                        } else {
                            f.x += vx;
                        }
                    }

                    if (f.startY >= f.targetY) {
                        if (f.y + vy <= f.targetY) {
                            f.y = f.targetY;
                            f.hitY = true;
                        } else {
                            f.y += vy;
                        }
                    } else {
                        if (f.y + vy >= f.targetY) {
                            f.y = f.targetY;
                            f.hitY = true;
                        } else {
                            f.y += vy;
                        }
                    }

                    if (f.hitX && f.hitY) {
                        self.createParticles(f.targetX, f.targetY, f.hue);
                        self.fireworks.splice(i, 1);

                    }
                }
                ;
            };

            self.drawFireworks = function () {
                var i = self.fireworks.length;
                self.ctx.globalCompositeOperation = 'lighter';
                while (i--) {
                    var f = self.fireworks[i];
                    self.ctx.lineWidth = f.lineWidth;

                    var coordRand = (rand(1, 3) - 1);
                    self.ctx.beginPath();
                    self.ctx.moveTo(Math.round(f.coordLast[coordRand].x), Math.round(f.coordLast[coordRand].y));
                    self.ctx.lineTo(Math.round(f.x), Math.round(f.y));
                    self.ctx.closePath();
                    self.ctx.strokeStyle = 'hsla(' + f.hue + ', 100%, ' + f.brightness + '%, ' + f.alpha + ')';
                    self.ctx.stroke();

                    if (self.showTarget) {
                        self.ctx.save();
                        self.ctx.beginPath();
                        self.ctx.arc(Math.round(f.targetX), Math.round(f.targetY), rand(1, 8), 0, Math.PI * 2, false)
                        self.ctx.closePath();
                        self.ctx.lineWidth = 1;
                        self.ctx.stroke();
                        self.ctx.restore();
                    }

                    if (self.showShockwave) {
                        self.ctx.save();
                        self.ctx.translate(Math.round(f.x), Math.round(f.y));
                        self.ctx.rotate(f.shockwaveAngle);
                        self.ctx.beginPath();
                        self.ctx.arc(0, 0, 1 * (f.speed / 5), 0, Math.PI, true);
                        self.ctx.strokeStyle = 'hsla(' + f.hue + ', 100%, ' + f.brightness + '%, ' + rand(25, 60) / 100 + ')';
                        self.ctx.lineWidth = f.lineWidth;
                        self.ctx.stroke();
                        self.ctx.restore();
                    }
                }
                ;
            };

            self.bindEvents = function () {
                $(window).on('resize', function () {
                    clearTimeout(self.timeout);
                    self.timeout = setTimeout(function () {
                        self.canvas.width = self.cw = $(window).innerWidth();
                        self.canvas.height = self.ch = $(window).innerHeight();
                        self.ctx.lineCap = 'round';
                        self.ctx.lineJoin = 'round';
                    }, 100);
                });
                
                $(window).on('load', function (e) {
                        
                          
                        setInterval(function(){
                        var max = $(window).width();
                        
                        self.mx = Math.random()*max;
                        self.my = Math.random()*450;
                        
                        //      startX, startY, targetX, targetY
                        self.createFireworks(self.cw / 2, self.ch, self.mx, self.my);
                        
                        },1000);
                         
                        
                   });
            }

            self.clear = function () {
                self.particles = [];
                self.fireworks = [];
                self.ctx.clearRect(0, 0, self.cw, self.ch);
            };


            self.canvasLoop = function () {
                requestAnimFrame(self.canvasLoop, self.canvas);
                self.ctx.globalCompositeOperation = 'destination-out';
                self.ctx.fillStyle = 'rgba(0,0,0,' + self.clearAlpha / 100 + ')';
                self.ctx.fillRect(0, 0, self.cw, self.ch);
                self.updateFireworks();
                self.updateParticles();
                self.drawFireworks();
                self.drawParticles();

            };

            self.init();

        }
        var fworks = new Fireworks();

    });

</script>

</body>
</html>
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