javascript - 向图像 slider 添加淡入淡出效果 - 纯 JavaScript

Question

所以，我知道 jQuery 使这变得非常简单，但我想弄清楚如何没有 js 库来做到这一点。当此 slider 中的图像发生变化时，如何合并淡入/淡出效果？我知道您可以使用点表示法更改不透明度，但我只是无法弄清楚这一切的逻辑。

var myImg = document.querySelector('.imgSlot'),
  myImgArray = ["images/x.jpg", "images/y.jpg", "images/z.jpg", "images/abc.jpg"],
  imgIndex = 0,
  varTimerSpeed = 4000,
  intervalHandle = setInterval(changeImg, varTimerSpeed);

function changeImg() {
  myImg.setAttribute('src', myImgArray[imgIndex]);
  imgIndex++;
   if ( imgIndex >= myImgArray.length) {
        imgIndex = 0;
  }
};

如有任何建议，我们将不胜感激，

大卫

Answer 1

您可以使用动画库来完成此操作。它使用 setTimeout 或 setInterval 函数每隔几毫秒对对象样式进行更改，从而产生动画。例如:

function moveElementToRight(el) {
    setInterval(function() {
       el.style.marginLeft = el.style.marginLeft + 10 //increase marginLeft by 10
    }),20) //every 20 milliseconds
}

一些基本逻辑:

var interval = 20 //milliseconds. Each 20 milliseconds = new frame.
var duration = 500 //milliseconds. Total time for the animation
var frames = Math.ceil(duration/interval) // frames count for the animation

您可以将此值与缓动函数一起使用，该函数将通过传递 (interval*i++ , from_value, to_value,uration); 返回当前帧的值；这里的“i”是通过循环帧计数获得的。 from_value 和 to_value 分别是元素的样式起始值和元素的样式结束值(这也可能应用于不透明度，这将导致淡入淡出效果)。

这是一个非常粗略的示例，但这是主要原理。对于缓动效果，您可以使用缓动函数。以下是一些:

    easeInQuad: function (t, b, c, d) {
        return c*(t/=d)*t + b;
    },
    easeOutQuad: function (t, b, c, d) {
        return -c *(t/=d)*(t-2) + b;
    },
    easeInOutQuad: function (t, b, c, d) {
        if ((t/=d/2) < 1) return c/2*t*t + b;
        return -c/2 * ((--t)*(t-2) - 1) + b;
    },
    easeOutCubic: function (t, b, c, d) {
        return c*((t=t/d-1)*t*t + 1) + b;
    },
    easeInOutCubic: function (t, b, c, d) {
        if ((t/=d/2) < 1) return c/2*t*t*t + b;
        return c/2*((t-=2)*t*t + 2) + b;
    },
    easeInQuart: function (t, b, c, d) {
        return c*(t/=d)*t*t*t + b;
    },
    easeOutQuart: function (t, b, c, d) {
        return -c * ((t=t/d-1)*t*t*t - 1) + b;
    },
    easeInOutQuart: function (t, b, c, d) {
        if ((t/=d/2) < 1) return c/2*t*t*t*t + b;
        return -c/2 * ((t-=2)*t*t*t - 2) + b;
    },
    easeInQuint: function (t, b, c, d) {
        return c*(t/=d)*t*t*t*t + b;
    },
    easeOutQuint: function (t, b, c, d) {
        return c*((t=t/d-1)*t*t*t*t + 1) + b;
    },
    easeInOutQuint: function (t, b, c, d) {
        if ((t/=d/2) < 1) return c/2*t*t*t*t*t + b;
        return c/2*((t-=2)*t*t*t*t + 2) + b;
    },
    easeInSine: function (t, b, c, d) {
        return -c * Math.cos(t/d * (Math.PI/2)) + c + b;
    },
    easeOutSine: function (t, b, c, d) {
        return c * Math.sin(t/d * (Math.PI/2)) + b;
    },
    easeInOutSine: function (t, b, c, d) {
        return -c/2 * (Math.cos(Math.PI*t/d) - 1) + b;
    },
    easeInExpo: function (t, b, c, d) {
        return (t==0) ? b : c * Math.pow(2, 10 * (t/d - 1)) + b;
    },
    easeOutExpo: function (t, b, c, d) {
        return (t==d) ? b+c : c * (-Math.pow(2, -10 * t/d) + 1) + b;
    },
    easeInOutExpo: function (t, b, c, d) {
        if (t==0) return b;
        if (t==d) return b+c;
        if ((t/=d/2) < 1) return c/2 * Math.pow(2, 10 * (t - 1)) + b;
        return c/2 * (-Math.pow(2, -10 * --t) + 2) + b;
    },
    easeInCirc: function (t, b, c, d) {
        return -c * (Math.sqrt(1 - (t/=d)*t) - 1) + b;
    },
    easeOutCirc: function (t, b, c, d) {
        return c * Math.sqrt(1 - (t=t/d-1)*t) + b;
    },
    easeInOutCirc:function (t, b, c, d) {
        if ((t/=d/2) < 1) return -c/2 * (Math.sqrt(1 - t*t) - 1) + b;
        return c/2 * (Math.sqrt(1 - (t-=2)*t) + 1) + b;
    },
    //a: amplitude (optional), p: period (optional)
    easeInElastic: function (t, b, c, d, a, p) {
        if (t===0) {return b;}
        if ((t/=d)==1) {return b+c;}
        if (!p) {p=d*0.3;}
        var s;
        if (a < Math.abs(c)) {
            a=c;
            s=p/4;
        }else {
            a=Math.abs(c);
            s = p/(2*Math.PI) * Math.asin(c/a);
        }
        return -(a*Math.pow(2,10*(t-=1)) * Math.sin( (t*d-s)*(2*Math.PI)/p )) + b;
    },
    easeOutElastic: function (t, b, c, d, a, p) {
        if (t===0) return b;
        if ((t/=d)==1) return b+c;
        if (!p) p=d*0.3;
        var s;
        if (a < Math.abs(c)) {
            a=c;
            s=p/4;
        }else {
            a=Math.abs(c);
            s = p/(2*Math.PI) * Math.asin (c/a);
        }
        return a*Math.pow(2,-10*t) * Math.sin( (t*d-s)*(2*Math.PI)/p ) + c + b;
    },
    easeInOutElastic: function (t, b, c, d, a, p) {
        if (t===0) return b;
        if ((t/=d/2)==2) return b+c;
        if (!p) p=d*(0.3*1.5);
        var s;
        if (a < Math.abs(c)) {
            a=c;
            s=p/4;
        }else {
            a=Math.abs(c);
            s = p/(2*Math.PI) * Math.asin (c/a);
        }
        if (t < 1) {
            return -0.5*(a*Math.pow(2,10*(t-=1)) * Math.sin( (t*d-s)*(2*Math.PI)/p )) + b;
        }
        return a*Math.pow(2,-10*(t-=1)) * Math.sin( (t*d-s)*(2*Math.PI)/p )*0.5 + c + b;
    },
    easeInBack: function (t, b, c, d, s) {
        if (s === undefined) s = 1.70158;
        return c*(t/=d)*t*((s+1)*t - s) + b;
    },
    easeOutBack: function (t, b, c, d, s) {
        if (s === undefined) s = 1.70158;
        return c*((t=t/d-1)*t*((s+1)*t + s) + 1) + b;
    },
    easeInOutBack: function (t, b, c, d, s) {
        if (s === undefined) s = 1.70158;
        if ((t/=d/2) < 1) return c/2*(t*t*(((s*=(1.525))+1)*t - s)) + b;
        return c/2*((t-=2)*t*(((s*=(1.525))+1)*t + s) + 2) + b;
    },
    easeInBounce: function (t, b, c, d) {
        return c - this.easeOutBounce (d-t, 0, c, d) + b;
    },
    easeOutBounce: function (t, b, c, d) {
        if ((t/=d) < (1/2.75)) {
            return c*(7.5625*t*t) + b;
        } else if (t < (2/2.75)) {
            return c*(7.5625*(t-=(1.5/2.75))*t + 0.75) + b;
        } else if (t < (2.5/2.75)) {
            return c*(7.5625*(t-=(2.25/2.75))*t + 0.9375) + b;
        } else {
            return c*(7.5625*(t-=(2.625/2.75))*t + 0.984375) + b;
        }
    },
    easeInOutBounce: function (t, b, c, d) {
        if (t < d/2) return this.easeInBounce (t*2, 0, c, d) * 0.5 + b;
        return this.easeOutBounce (t*2-d, 0, c, d) * 0.5 + c*0.5 + b;
    }

未经测试的示例:

function animate(element, property, start, end, interval, duration) {
    var frames = Math.ceil(duration/interval);
    for(i=0;i<=frames;i++) {
       (function(f){
           setTimeout(function() {
              element.style[property] = easing_function_from_above(interval*f, start, end,   duration);
           }, interval);
       })(i);
   }
}