使用关键帧创建循环动画

Question

I am working on a CSS only slider. However I don't have much experience with using keyframes.

I found this pen; could someone explain to me how the keyframes ensure that the animation runs in a cyclic manner rather than at the same time (where all the slides would disappear and reappear together)?

Code pen link

 .slider { max-width: 300px; height: 200px; margin: 20px auto; position: relative; } .slide1, .slide2, .slide3, .slide4, .slide5 { position: absolute; width: 100%; height: 100%; } .slide1 { background: url(http://media.dunkedcdn.com/assets/prod/40946/580x0-9_cropped_1371566801_p17tbs0rrjqdt1u4dnk94fe4b63.jpg)no-repeat center; background-size: cover; animation: fade 8s infinite; -webkit-animation: fade 8s infinite; } .slide2 { background: url(http://media.dunkedcdn.com/assets/prod/40946/580x0-9_cropped_1371565525_p17tbqpu0d69c21hetd77dh483.jpeg)no-repeat center; background-size: cover; animation: fade2 8s infinite; -webkit-animation: fade2 8s infinite; } .slide3 { background: url(http://media.dunkedcdn.com/assets/prod/40946/580x0-9_cropped_1371564896_p17tbq6n86jdo3ishhta3fv1i3.jpg)no-repeat center; background-size: cover; animation: fade3 8s infinite; -webkit-animation: fade3 8s infinite; } @keyframes fade { 0% { opacity: 1 } 33.333% { opacity: 0 } 66.666% { opacity: 0 } 100% { opacity: 1 } } @keyframes fade2 { 0% { opacity: 0 } 33.333% { opacity: 1 } 66.666% { opacity: 0 } 100% { opacity: 0 } } @keyframes fade3 { 0% { opacity: 0 } 33.333% { opacity: 0 } 66.666% { opacity: 1 } 100% { opacity: 0 } } 

 <div class='slider'> <div class='slide1'></div> <div class='slide2'></div> <div class='slide3'></div> </div> 

Answer 1

This is due to the each slide using a different keyframe, ie slide1 uses fade , slide2 uses fade2 and slide3 uses fade3 . These keyframes all last 8 seconds however the frame in which the slide is shown is different:

• slide1 is shown at 0% (0 seconds)
• slide2 is shown at 33.333% (about 2.6 seconds)
• slide3 is shown at 66.666% (about 5.3 seconds)

This particular method will work when you have three slides but would need to be adapted if you were to have a different amount. For example with four you would need to add an extra step to the keyframe:

 .slider { max-width: 300px; height: 200px; margin: 20px auto; position: relative; } .slide1, .slide2, .slide3, .slide4, .slide5 { position: absolute; width: 100%; height: 100%; } .slide1 { background: url(http://media.dunkedcdn.com/assets/prod/40946/580x0-9_cropped_1371566801_p17tbs0rrjqdt1u4dnk94fe4b63.jpg)no-repeat center; background-size: cover; animation: fade 8s infinite; -webkit-animation: fade 8s infinite; } .slide2 { background: url(http://media.dunkedcdn.com/assets/prod/40946/580x0-9_cropped_1371565525_p17tbqpu0d69c21hetd77dh483.jpeg)no-repeat center; background-size: cover; animation: fade2 8s infinite; -webkit-animation: fade2 8s infinite; } .slide3 { background: url(http://media.dunkedcdn.com/assets/prod/40946/580x0-9_cropped_1371564896_p17tbq6n86jdo3ishhta3fv1i3.jpg)no-repeat center; background-size: cover; animation: fade3 8s infinite; -webkit-animation: fade3 8s infinite; } .slide4 { background: red; background-size: cover; animation: fade4 8s infinite; -webkit-animation: fade4 8s infinite; } @keyframes fade { 0% { opacity: 1 } 25% { opacity: 0 } 50% { opacity: 0 } 75% { opacity: 0 } 100% { opacity: 1 } } @keyframes fade2 { 0% { opacity: 0 } 25% { opacity: 1 } 50% { opacity: 0 } 75% { opacity: 0 } 100% { opacity: 0 } } @keyframes fade3 { 0% { opacity: 0 } 25% { opacity: 0 } 50% { opacity: 1 } 75% { opacity: 0 } 100% { opacity: 0 } } @keyframes fade4 { 0% { opacity: 0 } 25% { opacity: 0 } 50% { opacity: 0 } 75% { opacity: 1 } 100% { opacity: 0 } } 

 <div class='slider'> <div class='slide1'></div> <div class='slide2'></div> <div class='slide3'></div> <div class='slide4'></div> </div> 

As suggested by @ILoveCSS this code can be shortened to just the one keyframe animation by adding a third property to the animation property. This value is the animation-delay property and will stall the animation by the specified time:

 .slider { max-width: 300px; height: 200px; margin: 20px auto; position: relative; } .slide1,.slide2,.slide3,.slide4,.slide5 { position: absolute; width: 100%; height: 100%; } .slide1 { background: url(http://media.dunkedcdn.com/assets/prod/40946/580x0-9_cropped_1371566801_p17tbs0rrjqdt1u4dnk94fe4b63.jpg)no-repeat center; background-size: cover; animation:fade 8s infinite; -webkit-animation:fade 8s infinite; } .slide2 { background: url(http://media.dunkedcdn.com/assets/prod/40946/580x0-9_cropped_1371565525_p17tbqpu0d69c21hetd77dh483.jpeg)no-repeat center; background-size: cover; animation:fade 8s infinite 2.6s; -webkit-animation:fade 8s infinite 2.6s; } .slide3 { background: url(http://media.dunkedcdn.com/assets/prod/40946/580x0-9_cropped_1371564896_p17tbq6n86jdo3ishhta3fv1i3.jpg)no-repeat center; background-size: cover; animation:fade 8s infinite 5.3s; -webkit-animation:fade 8s infinite 5.3s; } @keyframes fade { 0% {opacity:1} 33.333% { opacity: 0} 66.666% { opacity: 0} 100% { opacity: 1} } 

 <div class='slider'> <div class='slide3'></div> <div class='slide2'></div> <div class='slide1'></div> </div> 

Answer 2

I think what he is trying is:

@keyframes fade
{
  0%   {opacity:1}
  33.333% { opacity: 0}
  66.666% { opacity: 0}
  100% { opacity: 1}
}

in this case slide1 is getting visible at the start of the animation and stops when it reached 33.333% and 66.666% and starts to visible at the end of the animation which is 100%.

@keyframes fade2
{
  0%   {opacity:0}
  33.333% { opacity: 1}
  66.666% { opacity: 0 }
  100% { opacity: 0}
}

in the second slide2 at the start of the animation is not showing because slide1 is in the playing of it's animation and when slide1 reaches 33.333% started to stop and slide2 will start to fadeIn.

@keyframes fade3
{
  0%   {opacity:0}
  33.333% { opacity: 0}
  66.666% { opacity: 1}
  100% { opacity: 0}
}

in the third slide3 the animation start to fadeIn at 66.666% because at this percent slide2 is in fadeOut state and it continue like this infinitely...

Hope you have an idea.