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Stack With Bind Ad

Summary

Sample AMPHTML ad using amp-bind, and amp-selector to create an interactive "stack" ad.

Styling

This is an advanced example that requires some styling to make it look and function properly.

We use custom CSS properties and calc() in this example for the sake of readability. This is not a requirement, since the results of all of the calc() expressions in this example can be replaced by hand or by using a CSS pre-processor.

<style amp-custom>
  /* Define constants for stack item dimensions */
  :root {
    --item-width: 230px;
    --item-height: 130px;
  }
  /* Root container for the entire visual area */
  .root-container {
    font-family: 'Roboto', sans-serif;
    font-size: 14px;
    background: #000;
    color: #fff;
    width: 100%;
    height: 100vh;
    position: relative;
    display: flex;
    flex-direction: column;
    overflow: hidden;
    -webkit-tap-highlight-color: rgba(0, 0, 0, 0);
  }
  /* Main area container */
  .main-container {
    flex: 1;
    display: flex;
    align-items: center;
    justify-content: center;
    flex-direction: column;
  }
  /* Footer styling */
  .footer {
    background: #000;
    font-size: 12px;
    padding: 8px;
    line-height: 34px;
    display: flex;
    position: relative;
    z-index: 1;
  }
  .footer-logo {
    flex: 1;
  }
  .logo-img {
    display: block;
  }
  .button {
    text-decoration: none;
    text-transform: uppercase;
    padding: 0 12px;
    color: #fff;
    display: inline-block;
    background-color: #2979ff;
  }
  /*
   * We use empty div elements to fake the appearance of depth in the stack.
   * Each one of them is offset by 8px, which is why the width changes.
   */
  .stack-bg-item {
    height: calc(var(--item-height) - 4px);
    margin: calc(8px - var(--item-height)) auto 0;
    border-radius: 3px;
  }
  .stack-bg-item:nth-child(1) {
    background: rgba(255, 255, 255, 0.15);
    margin-top: 0;
    width: calc(var(--item-width) - 4 * 8px);
  }
  .stack-bg-item:nth-child(2) {
    background: rgba(255, 255, 255, 0.25);
    width: calc(var(--item-width) - 3 * 8px);
  }
  .stack-bg-item:nth-child(3) {
    background: rgba(255, 255, 255, 0.35);
    width: calc(var(--item-width) - 2 * 8px);
  }
  .stack-bg-item:nth-child(4) {
    background: rgba(255, 255, 255, 0.45);
    width: calc(var(--item-width) - 1 * 8px);
  }
  .stack-container {
    display: block;
    position: absolute;
  }
  .stack {
    height: var(--item-height);
    width: var(--item-width);
    margin: calc(5px - var(--item-height)) 0 5px;
  }
  /* Styling for actual stack items */
  .stack-item {
    height: var(--item-height);
    width: var(--item-width);
    background: rgba(255, 255, 255, 0.6);
    border-radius: 3px;
    padding: 2px;
    position: absolute;
    box-sizing: border-box;
    transition: 0.3s transform, 0.3s opacity;

    /*
     * Translate the stack item horizontally when not topmost or second
     * topmost, and set its opacity to 0 so it's out of view.
     */
    transform: translate(100px, 0);
    opacity: 0;
  }
  .stack-item:nth-child(even) {
    /*
     * We use negative translate for each even stack item to alternate the
     * animation effect.
     */
    transform: translate(-100px, 0);
  }
  /*
   * Style the second topmost stack item so it's displayed.
   * We scale it so it's smaller than the topmost element by 8px total, to
   * contribute to the illusion of depth.
   */
  .stack-item.second-topmost {
    transform: scale(calc(1 - (4px / var(--item-width)))) translate(0, 0);
    opacity: 0;
  }
  /*
   * Style the topmost stack item so it's in full-width and slightly offset
   * from the second topmost.
   */
  .stack-item.topmost {
    opacity: 1;
    transform: scale(1) translate(0, 4px);
    z-index: 1;
  }
  /* Styling for selector dots */
  .dots {
    text-align: center;
  }
  .dots-item {
    display: inline-block;
    width: 6px;
    height: 6px;
    border-radius: 6px;
    background: #fff;
    margin: 0 2px;
  }
  .dots-item[selected] {
    background: #2979ff;
  }
  .bg-img-container {
    width: 100%;
  }
</style>

amp-bind state configuration

We use the initial state to configure the amount of items in stack.

<amp-state id="config">
  <script type="application/json">
    {
      "length": 5
    }
  </script>
</amp-state>

Main container

Define a main container with an amp-img as background

<div class="root-container">
  <div class="main-container">
    <div class="bg-img-container">
      <amp-img src="/static/samples/img/car-front.jpg"
        width="608"
        height="568"
        layout="responsive"
        class="bg-img"></amp-img>
    </div>

Stack

AMP has a system in place for events and actions. It uses a domain-specific language to describe how actions are triggered. In this example, we set the on attribute so the amp-bind state changes on tap. The selection variable is originally undefined, which means that when it is accessed by the first time, it will fallback to zero. The remainder operation (%) is used so that the stack will cycle back to zero once the final element is at the top.

Each stack item has a conditional class value ([class]) that is calculated by amp-bind. This is to determine whether each item is the topmost or the second-topmost element in the stack so it can be styled appropriately.

See this document for specifics on the amp-bind expression syntax.

<div class="stack-container"
  role="button"
  on="tap:AMP.setState({selection: (selection + 1) % config.length})">
  <div class="stack-bg-item"></div>
  <div class="stack-bg-item"></div>
  <div class="stack-bg-item"></div>
  <div class="stack-bg-item"></div>
  <div class="stack">
    <div class="stack-item topmost"
      [class]="'stack-item' +
              (selection == 0 ? ' topmost' :
                  (selection == config.length - 1 ? ' second-topmost' : ''))">
      <amp-img src="/static/samples/img/car-sideview.jpg"
        width="226"
        height="126"
        layout="fixed"></amp-img>
    </div>
    <div class="stack-item second-topmost"
      [class]="'stack-item' +
              (selection == 1 ? ' topmost' :
                  (selection == 0 ? ' second-topmost' : ''))">
      <amp-img src="/static/samples/img/car-steeringwheel.jpg"
        width="226"
        height="126"
        layout="fixed"></amp-img>
    </div>
    <div class="stack-item"
      [class]="'stack-item' +
            (selection == 2 ? ' topmost' :
                (selection == 1 ? ' second-topmost' : ''))">
      <amp-img src="/static/samples/img/car-seats.jpg"
        width="226"
        height="126"
        layout="fixed"></amp-img>
    </div>
    <div class="stack-item"
      [class]="'stack-item' +
            (selection == 3 ? ' topmost' :
                (selection == 2 ? ' second-topmost' : ''))">
      <amp-img src="/static/samples/img/car-gauges.jpg"
        width="226"
        height="126"
        layout="fixed"></amp-img>
    </div>
    <div class="stack-item"
      [class]="'stack-item' +
            (selection == 4 ? ' topmost' :
                (selection == 3 ? ' second-topmost' : ''))">
      <amp-img src="/static/samples/img/car-engine.jpg"
        width="226"
        height="126"
        layout="fixed"></amp-img>
    </div>
  </div>

We can use amp-selector to show indicator dots for our stack. The [selected] attribute is used to refer to an amp-bind state variable so that the indicators change accordingly.

<amp-selector layout="container"
  class="dots"
  disabled
  [selected]="selection">
  <div option="0"
    class="dots-item"
    selected></div>
  <div option="1"
    class="dots-item"></div>
  <div option="2"
    class="dots-item"></div>
  <div option="3"
    class="dots-item"></div>
  <div option="4"
    class="dots-item"></div>
</amp-selector>
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