How to set keyframes name in LESS

问题:

I try to set up this LESS mixin for CSS animation keyframes:

.keyframes(@name, @from, @to) {;
  @-webkit-keyframes "@name" {
    from {
      @from;  
    }
    to {
      @to;
    }
  }
}

but there is some problem with name pharse, is there any option to do this corectly?

回答1:

As of LESS >= 1.7 you can use variables for keyframe keywords (names).

Some changes have been made in LESS 1.7 to how directives work, which allows to use variables for the name/keyword of @keyframes (so the example from the question should work now). DEMO

---

Unfortunately keyframes names can not be dynamically generated in LESS <= 1.6

Hence, the normal way of going about keyframes would use hardcoded names and you would only call for specific "for" and "to" mixins, like this:

.colors-mixin-frame(@from,@to){
from {color: @from;}
to {color: @to;}
}

.width-mixin-frame(@from,@to){
from {width: @from;}
to {width: @to;}
}

// keyframes with hardcoded names calling for specific mixin frames
@keyframes red-blue { .colors-mixin-frame(red, blue); }
@keyframes change-width { .width-mixin-frame(254px, 512px); }

---

But you can use a workaround to dynamically generate the names

where you inject the name into the rule name, this however requires an declaration of the next rule that supplies the closing bracket } at the end of the keyframes declaration. The most convenient is if you just build the animation calling that keyframe

.animation-keyframes(@name, @from, @to, @anim-selector) {
  @keyf: ~"@keyframes @{name} { `'\n'`from ";
  @anim: ~"} `'\n'`.@{anim-selector}";
  @{keyf} {
      .from(@name,@from);
        }
      to {
        .to(@name,@to);
      }
  @{anim} {
    animation-name:@name;
  }
}

Note that you also need to define .from(){} and .to(){} mixins, and not just use @from and @to like you did in your example (because LESS also does not allow for dynamically generated properties) ... this mixins can now construct the desired properties and values ... to use specific property you can use guards or name-specific mixins like these:

// name-specific from and to mixins that are used if first argument equals "colors"
.from (colors, @color) {
  color: @color;
}
.to (colors, @color) {
  color: @color;
} 

Now we can call our mixin in LESS:

// test
.animation-keyframes (colors, red, blue, my-colanim);

and get CSS:

@keyframes colors { 
from {
  color: #ff0000;
}
to {
  color: #0000ff;
}
} 
.my-colanim {
  animation-name: colors;
}

this will work also in LESS 1.4, but note that we used javascript interpolation for line breaks, which requires a javascript implementation of LESS.

---

Edit: to your additional question about prefixes

Mixin with vendor prefixes

Here I made two mixins ... one without vendor prefixes and one with them both calling a general .keyframes mixin:

.keyframes (@name, @from, @to, @vendor:"", @bind:"") {
  @keyf: ~"@{bind}@@{vendor}keyframes @{name} { `'\n'`from ";
  @{keyf} {
      .from(@name,@from);
        }
      to {
        .to(@name,@to);
      }
}

.animation-keyframes-novendor (@name, @from, @to, @anim-selector) {
  .keyframes (@name, @from, @to);
  @anim: ~"} `'\n'`.@{anim-selector}";
  @{anim} {
    animation-name:@name;
  }
}

.animation-keyframes (@name, @from, @to, @anim-selector) {
  @bind: "} `'\n'`";
  .keyframes (@name, @from, @to, "-moz-");
  .keyframes (@name, @from, @to, "-webkit-", @bind);
  .keyframes (@name, @from, @to, "-o-", @bind);
  .keyframes (@name, @from, @to, "-ms-", @bind);
  .keyframes (@name, @from, @to, "", @bind);
  @anim: ~"} `'\n'`.@{anim-selector}";
  @{anim} {
    -moz-animation: @name;
    -webkit-animation: @name;
    -o-animation: @name;
    -ms-animation: @name;
    animation: @name;
  }
}

.from (colors, @color) {
  color: @color;
}
.to (colors, @color) {
  color: @color;
}

/* keyframes with all vendor prefixes */
.animation-keyframes (colors, red, blue, my-colanim);

/* keyframes with no vendor prefix */
.animation-keyframes-novendor (colors, red, blue, my-colanim);

The .animation-keyframes will now produce keyframes for all vendor prefixes and an animation selector with vendor prefixed properties. And as expected the .animation-keyframes-novendor gives the same output as the above simple solution (without vendor prefixes).

---

Some notes:

• For your animation to actually work you need to set other animation parameters like timing-function, duration, direction, iteration-count (requires at least a duration time in addition to the name that we already set).

  For example:

   animation: @name ease-in-out 2s infinite alternate;

• If you wrap above mixins in namespaces make sure you change the mixin references inside other mixins to their whole path (including the namespaces).

  For example:

   #namespace > .keyframes () // see .less source in the demo for details

DEMO

回答2:

I am currently working on a mixin library

The source can be found here https://github.com/pixelass/more-or-less

My keyframe mixin looks like this:

WORKS FOR LESS 1.7.x

MIXIN

.keyframes(@name) { 
    @-webkit-keyframes @name {
        .-frames(-webkit-);
    }
    @-moz-keyframes @name {
        .-frames(-moz-);
    }
    @keyframes @name {
        .-frames();
    }
}

INPUT

& {
    .keyframes(testanimation);.-frames(@-...){
        0% {
            left: 0;
            @{-}transform: translate(10px, 20px);
        }

        100% {
            left: 100%;
            @{-}transform: translate(100px, 200px);
        }
    }
}

OUTPUT

@-webkit-keyframes testanimation {
  0% {
    left: 0;
    -webkit-transform: translate(10px, 20px);
  }
  100% {
    left: 100%;
    -webkit-transform: translate(100px, 200px);
  }
}
@-moz-keyframes testanimation {
  0% {
    left: 0;
    -moz-transform: translate(10px, 20px);
  }
  100% {
    left: 100%;
    -moz-transform: translate(100px, 200px);
  }
}
@keyframes testanimation {
  0% {
    left: 0;
    transform: translate(10px, 20px);
  }
  100% {
    left: 100%;
    transform: translate(100px, 200px);
  }
}

回答3:

How about this:

@-webkit-keyframes some-animation {.mixi-frames;}
@-moz-keyframes some-animation {.mixi-frames;}
@-ms-keyframes some-animation {.mixi-frames;}
@-o-keyframes some-animation {.mixi-frames;}
@keyframes some-animation {.mixi-frames;}

.mixi-frames () {
    from {width: 254px;}
    to {width: 512px;}
}

You need to do it for each animation. Taken from: http://radiatingstar.com/css-keyframes-animations-with-less

回答4:

Also thanks to the great answer by Martin Turjak, (thank you for that) I just put on github a less mixin which generate keyframes and animation's css code without hacks and in a flexible way, you can find it here github.com/kuus/animate-me.less.

With this mixin you can write this code to obtain valid and cross browser css (see the github repo for a complete explanation):

.animate-me(ComplexAnimation; 0.4s ease; '.complex-animation';
    '50%, 100%'; '%stransform: translateZ(-250px) rotateY(30deg)';
    70%; '%stransform: translateZ(-250px) rotateY(30deg); opacity: .5; background:   green';
    30%; '%stransform: translateZ(-250px) rotateY(30deg); opacity: .2; background: yellow';
    80%; '%stransform: translateZ(-250px) rotateY(30deg); opacity: 1; background: red'
);

回答5:

Before-mentioned https://github.com/kuus/animate-me.less does things!

You can also check out this one written by me (seems to be neater): https://github.com/thybzi/keyframes

回答6:

I think you should do this

@-webkit-keyframes @name 
{
 code...
}

change "@name" to @name

and you should delete ; after

.keyframes(@name, @from, @to) {