[英]Adding fade effects to img slider - pure JavaScript
因此,我知道jQuery使此超级简单,但是我想弄清楚如何在没有 js库的情况下执行此操作。 当此滑块中的图像改变时,如何合并淡入/淡出效果? 我知道您可以使用点表示法来更改不透明度,但我只是无法弄清这一切的逻辑。
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;
}
};
任何建议将不胜感激,
大卫
您可以通过使用动画库来实现。 它使用setTimeout或setInterval函数每隔几毫秒将更改应用于对象的样式,从而生成动画。 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,duration)返回当前帧的值; 这里“ i”是通过循环帧计数获得的。 From_value和to_value是元素的样式开始值和元素的样式结束值(这也可以用于不透明度,这将导致褪色效果)。
这是非常粗糙的示例,但这是主要原理。 要获得缓动效果,可以使用缓动功能。 这里有一些:
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);
}
}
这是一个好问题。 它无疑帮助我学习了很多东西。 事不宜迟,这是我想出的:
注意 :这仅用于淡入淡出,这对其他样式的动画无济于事
var fade = function (elementInDocument, fadeTo, amountOfTime) {
var start = new Date().getTime(), //start with the beginning time
getOpacity = function () {
//returns the current opacity of the given element
var cs = window.getComputedStyle(elementInDocument),
co = cs.getPropertyValue('opacity');
return parseFloat(co, 10); //getPropertyValue returns a string,
//so you need to float it
},
startingOpacity = getOpacity(), //the beginning opacity of the element
diff = fadeTo - startingOpacity, //the difference between what you want the opacity to be
//and the beginning opacity
timer = setInterval(function () {
var co = getOpacity(), //start by getting the current opacity (each interval)
runTime = new Date().getTime() - start, //the amount of time the function has run
progress = runTime / amountOfTime; //the progress of the function
if (progress >= 1) {
clearInterval(timer); //stop the function because we have completed fade
}
//takes the beginning opacity and adds it to the product of the difference (diff)
//and progress of the function
elementInDocument.style.opacity = startingOpacity + (diff * progress);
}, 10);
};
//Then to call it
fade(document.getElementById("someElement"), .6, 3000);
我试图尽可能详细地解释。
这是一些测试用例的小提琴: http : //jsfiddle.net/9U9h8/4/
另一个重要说明 :这不是跨浏览器,尤其是在较旧的浏览器上(看着您IE <9)
我知道您已经要求使用纯JavaScript,但是如果您尝试使用jQuery会更好,因为jQuery可以处理跨浏览器的兼容性。
您可以尝试如下操作:
$("#"+elem).fadeOut(1000, function () {
var img = imgArr[currIndex];
$("#"+elem).attr("src",img);
$("#"+elem).fadeIn(1000);
});
它利用了jQuery的fadeIn和fadeOut机制来控制透明度。 检查下面的工作示例。
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