Clip-path and SVG rect inside animation

Question

I am trying to make a fancy animation only in CSS. I started with a tutorial on W3 School and wanted to make it better. My idea is to have a square loader turning clockwise while another inside would turn in the opposite direction.

On this link you will see what I'm talking about, the only difference is that I would like the red part to be turning in the opposite direction.

In order to do so I tried adding another div with class name .spinner. Here's my try at it: https://jsfiddle.net/avhjj4ps/

.loader-container {
  position: absolute;
  left: calc(50% - 75px);
  width: 150px;
  height: 150px;
  padding: 5px;
  border: 1px solid red;
  top: calc(50% - 75px);
}
img {
  width: 200px;
  margin: 20px;
  /*animation: move 2s alternate infinite linear;*/
}

#myClip, #svg {
  position: absolute;
  left: 50%;
  top: 50%;
}


.loader, .spinner {
position: absolute;

}
.loader {
  left: calc(50% - 35px);
  top: calc(50% - 35px);
  width: 40px;
  height: 40px;
  border: 15px solid transparent;
  border-top: 15px solid none;
  /*-webkit-animation: loader 2s linear infinite;
  animation: loader 2s linear infinite;*/
}
.spinner {
  left: calc(50% - 55.1px);
  top: calc(50% - 55.1px);
  /*clip-path: url(#myClip);*/
  width: 40px;
  border-radius: 50%;
  height: 40px;
  border: 36px solid #f3f3f3;
  border-top: 36px solid #5cb85c;
  /*-webkit-animation: spin 2s linear infinite;
  animation: spin 2s linear infinite;*/
}

@-webkit-keyframes loader {
  0% { -webkit-transform: rotate(0deg); }
  100% { -webkit-transform: rotate(360deg); }
}

@keyframes loader {
  0% { transform: rotate(0deg); }
  100% { transform: rotate(360deg); }
}

@-webkit-keyframes spin {
  0% { -webkit-transform: rotate(0deg); }
  100% { -webkit-transform: rotate(-360deg); }
}

@keyframes spin {
  0% { transform: rotate(0deg); }
  100% { transform: rotate(-360deg); }
}

<div class="loader-container">
 <div class="loader"></div>
<div class="spinner"></div>
  
<svg id="svg" width="0" height="0">
  <defs>
    <clipPath id="myClip">
      <rect x="-35" y="-35" width="15" height="70" />
      <rect x="20" y="-35" width="15" height="70" />
      <rect x="-35" y="-35" width="70" height="15" />
      <rect x="-35" y="20" width="70" height="15" />
      
    </clipPath>
  </defs>
</svg>
  
</div>

I am trying to show the green spinner only where there is the square loader. It would be like a mask. In the above snippet (also available here: http://codepen.io/anon/pen/ZOoByA), I'm trying to use the clip-path property. Can some tell me why clip-path: url(#myClip); doesn't work ? When I comment this line the loader shows completely, however while active it's not showing at all.

Answer 1

For a CSS-only solution without SVG you need some helper elements:

<div class="loader">
    <div class="square"></div>
    <div class="cutter">
        <div class="spinner">
        </div>
    </div>
</div>

And then this CSS code:

.square {
  width: 40px;
  height: 40px;
  background: #f3f3f3;
  z-index: 1;
}

.cutter {
  width: 70px;
  height: 70px;
  left: -15px;
  top: -15px;
  overflow: hidden;
}

.spinner {
  width: 54px;
  border-radius: 50%;
  height: 54px;
  border: 8px solid transparent;
  border-top: 8px solid #5cb85c;
  -webkit-animation: spin 1s linear infinite;
  animation: spin 1s linear infinite;
  margin-left: -15px;
  margin-top: -15px;
}

Result: https://jsfiddle.net/avhjj4ps/3/

Disadvantage: Inner square must have a solid background (no gradient or image) if it has to match the parent's / body's background.

Answer 2

You can create your loader in svg with some polygons and then clip the inner green loader away with clipPath.

First, define the gray border as a polygon:

<polygon id="loader" points="0,0 0,70 70,70 70,0 0,0 15,15 55,15 55,55 15,55 15,15" />

As we will reuse this shape (the actual loader and the clip-path shape), we put into the defs tag:

<svg height="0" width="0">
    <defs>
        <polygon id="loader" points="..." />
    </defs>
</svg>

Then we put the clipPath into the same defs tag:

<clipPath id="loaderClipper">
    <use xlink:href="#loader" x="15" y="15" />
</clipPath>

The offset of 15 is calculated in the following way: The loader's width is 70, but if it is rotated by 45 degrees, it's width is 70√2 which rounds to 100. The whitespace in the left and in the right is (100 - 70) / 2 = 15.

The svg for the actual used element looks like this:

<svg width="100" height="100" viewbox="0 0 100 100" clip-path="url(#loaderClipper)">
    <use xlink:href="#loader" class="loader" x="15" y="15" />
    <polygon class="spinner" points="0,0 100,0 50,50" x="30" y="30" />
</svg>

And some css for colors and the animation:

svg {
  animation: rotate 2s linear infinite;
  transform-origin: 50px 50px;
}

.loader {
  fill: #dcdada;
}

.spinner {
  fill: #5cb85c;
  animation: rotate 1s linear infinite reverse;
  transform-origin: 50px 50px;
}

Result fiddle: https://jsfiddle.net/apLepsv3/10/

Successfully tested on both mobile and desktop Firefox and Chrome.

Answer 3

You can create the spinner with HTML and CSS and then cut the overflow away by using the clip-path property in combination with a svg <clipPath> element.

Your html structure of the spinner:

<div class="loader">
    <div class="spinner">
    </div>
</div>

Now position the two elements over each other:

.loader {
  width: 40px;
  height: 40px;
  position: relative;
  left: 30px;
  top: 30px;
  border: 15px solid #dcdada;
  border-top: 15px solid none;
  -webkit-animation: loader 2s linear infinite;
  animation: loader 2s linear infinite;
}

.spinner {
  width: 0px;
  height: 0px;
  position: relative;
  left: -30px;
  top: -30px;
  border: 50px solid transparent;
  border-top: 50px solid #5cb85c;
  -webkit-animation: spin 1s linear infinite;
  animation: spin 1s linear infinite;
}

But there's still that green overflow outside and inside of the gray border. So we need to cut it away with a svg <polygon>.

<svg height="0" width="0">
    <defs>
        <clipPath id="loaderClipper">
            <polygon points="0,0 0,70 70,70 70,0 0,0 15,15 55,15 55,55 15,55 15,15"/>
        </clipPath>
    </defs>
</svg>

The points define a 70x70 square with a 40x40 square cut off.

Then add the clip-path property that references to the svg <clipPath> element:

.loader {
  clip-path: url(#loaderClipper);
}

Fiddle: https://jsfiddle.net/apLepsv3/2/

Disadvantage: Only supported in Firefox, not Chrome