Jerking animation on css3 spinner

Question

I found one attractive spinner(CSS3, SCSS): http://codepen.io/weaintplastic/pen/qEMZbx.

@for $i from 1 through 6 {
    @keyframes preload-show-#{$i}{
        from{
            transform: rotateZ(60* $i + deg) rotateY(-90deg) rotateX(0deg);
            border-left-color: #9c2f2f;
        }
    }
    @keyframes preload-hide-#{$i}{
        to{
            transform: rotateZ(60* $i + deg) rotateY(-90deg) rotateX(0deg);
            border-left-color: #9c2f2f;
        }
    }

    @keyframes preload-cycle-#{$i}{

        $startIndex: $i*5;
        $reverseIndex: (80 - $i*5);

        #{$startIndex * 1%}{
            transform: rotateZ(60* $i + deg) rotateY(90deg) rotateX(0deg);
            border-left-color: #9c2f2f;
        }
        #{$startIndex + 5%},
        #{$reverseIndex * 1%}{
            transform: rotateZ(60* $i + deg) rotateY(0) rotateX(0deg);
            border-left-color: #f7484e;
        }

        #{$reverseIndex + 5%},
        100%{
            transform: rotateZ(60* $i + deg) rotateY(90deg) rotateX(0deg);
            border-left-color: #9c2f2f;
        }
    }
}

@keyframes preload-flip{
    0%{
        transform: rotateY(0deg) rotateZ(-60deg);
    }
    100%{
        transform: rotateY(360deg) rotateZ(-60deg);
    }
}

body{
  background: #efefef;
}

.preloader{
  position: absolute;
  top: 50%;
  left: 50%;
    font-size: 20px;
    display: block;
    width: 3.75em;
    height: 4.25em;
    margin-left: -1.875em;
  margin-top: -2.125em;
    transform-origin: center center;
    transform: rotateY(180deg) rotateZ(-60deg);

    .slice{
        border-top: 1.125em solid transparent;
        border-right: none;
        border-bottom: 1em solid transparent;
        border-left: 1.875em solid #f7484e;
        position: absolute;
        top: 0px;
        left: 50%;
        transform-origin: left bottom;
        border-radius: 3px 3px 0 0;
    }

    @for $i from 1 through 6 {
      .slice:nth-child(#{$i}) { 
        transform: rotateZ(60* $i + deg) rotateY(0deg) rotateX(0);
        animation: .15s linear .9 - $i*.08s preload-hide-#{$i} both 1;
      }
    }


    &.loading{
        animation: 2s preload-flip steps(2) infinite both;
        @for $i from 1 through 6 {
          .slice:nth-child(#{$i}) { 
            transform: rotateZ(60* $i + deg) rotateY(90deg) rotateX(0);
            animation: 2s preload-cycle-#{$i} linear infinite both;
          }
        }
    }

}

<div class="preloader loading">
  <span class="slice"></span>
  <span class="slice"></span>
  <span class="slice"></span>
  <span class="slice"></span>
  <span class="slice"></span>
  <span class="slice"></span>
</div>

But it has the jerking moment(glitch) in the middle of animation: bottom part of hexagon moves to right on one or two pixels.

I took video of this moment: youtu.be/_TwDuxME8wc.

I tried to repair it on my own, but I haven't enough skills. Could you prompt how it can be fixed? Thanks!

Answer 1

You use a lot of em measurements, which results in a lot of decimal pixel values. It's important that you only have integer values to avoid these glitches.

If you take @Nick Barlett's solution and change the font-size of .preloader from 20px to 24px you will get rid of the decimal values. See this pen: http://codepen.io/pstenstrm/pen/mJJpvP

This will of course make the loader bigger too, so you might want to change the em values to px.

Answer 2

Change the 100% state on the preload-flip to have rotateZ(64deg)

@keyframes preload-flip{
    0%{
        transform: rotateY(0deg) rotateZ(-60deg);
    }
    100%{
        transform: rotateY(360deg) rotateZ(-64deg);
    }
}

There seems to be a bigger issue overall with the angles, though, as the pen is slightly askew to begin with.

Answer 3

@pstenstrm's solution brilliantly resolves the glitch problem, +1.

It introduces another problem, though:

In Firefox (only?), there is an ugly jagged border in the top left triangle.

To solve it, just add a trasparent outline to the triangles:

.slice{
  outline: 1px solid transparent;
}

Check out the demo to see the final result:

Running demo