timeline-trigger-activation-range-start CSS property

Syntax

css

/* Keyword or <length-percentage> */
timeline-trigger-activation-range-start: normal;
timeline-trigger-activation-range-start: 20%;
timeline-trigger-activation-range-start: 350px;

/* Named timeline range value */
timeline-trigger-activation-range-start: cover;
timeline-trigger-activation-range-start: exit;
timeline-trigger-activation-range-start: entry 40%;
timeline-trigger-activation-range-start: contain 200px;

/* Multiple range start values */
timeline-trigger-activation-range-start:
  contain,
  entry 50%;

/* Global values */
timeline-trigger-activation-range-start: inherit;
timeline-trigger-activation-range-start: initial;
timeline-trigger-activation-range-start: revert;
timeline-trigger-activation-range-start: revert-layer;
timeline-trigger-activation-range-start: unset;

The timeline-trigger-activation-range-start property is specified as one or more values, separated by commas.

Values

normal: Represents the start of the timeline. This is the default value.
<length-percentage>: Specifies a length or percentage value measured from the beginning of the timeline.
<timeline-range-name>: Specifies a named timeline range within the overall timeline. The range starts at 0%.
<timeline-range-name> <length-percentage>: Specifies a length or percentage value measured from the beginning of the specified named timeline range.

When creating CSS scroll-triggered animations, the timeline-trigger-activation-range-start property can be used to explicitly define the start of the trigger's activation range. Read the linked guide and the timeline-trigger-activation-range description for more information.

Allowed values for the timeline-trigger-activation-range-start property are:

normal
A <length-percentage>
A <timeline-range-name>
A <timeline-range-name> and a <length-percentage> separated by a space.

If the <timeline-range-name> value does not include a <length-percentage>, the percentage defaults to 0%.

The timeline-trigger-activation-range-start, along with the timeline-trigger-activation-range-end property, can both be set in a single declaration using the timeline-trigger-activation-range shorthand.

Specifying multiple range start values

When multiple values are specified in a single timeline-trigger-activation-range-start property, they are distributed between the specified timeline-trigger-name values in the same fashion as multiple animation values are distributed (see Setting multiple animation property values).

If multiple timeline-trigger-name values are set, but only a single timeline-trigger-activation-range-start value is set, the timeline-trigger-activation-range-start will apply to all the timeline-trigger-names. If two timeline-trigger-activation-range-start values are set, they will cycle between the timeline-trigger-names until all of them have a timeline-trigger-activation-range-start value set. And so on.

For example, consider these declarations:

css

timeline-trigger-name: --my-trigger, --my-other-trigger, --another-trigger;
timeline-trigger-activation-range-start:
  cover,
  entry 40%;

In this case, the first name will use the cover range start, and the second name will use the entry 40% range start. The third name will cycle back to using the cover range start again.

Formal definition

Value not found in DB!

Formal syntax

timeline-trigger-activation-range-start = 
  [ normal | <length-percentage> | <timeline-range-name> <length-percentage>? ]#  

<length-percentage> = 
  <length>      |
  <percentage>

Examples

Basic usage

In this example, we show how to create a basic scroll-triggered animation with a custom activation range start value.

HTML

Our markup contains two <div> elements, plus some basic text content to cause the page to scroll. We have hidden the text content for brevity.

html

<div class="animated">I am animated</div>

...

<div class="trigger">I create the trigger</div>

...

<div class="animated">I am animated</div>

<p>
  Fusce dictum ex quis ipsum consectetur placerat. Cras sed lectus ex. Quisque
  purus dolor, vulputate ac mi eget, commodo varius odio. Suspendisse faucibus
  ipsum vel libero finibus, in placerat nibh congue. Sed iaculis, metus et
  euismod posuere, mi diam vestibulum felis, ac vulputate eros ipsum id justo.
  Etiam a tincidunt purus. Maecenas semper sed enim at blandit. Aenean ut
  sagittis lorem, eget gravida purus. Phasellus eleifend, lectus nec pulvinar
  facilisis, dui dolor feugiat odio, iaculis tempor felis est non tortor. In
  suscipit lorem efficitur molestie tempus. Integer sit amet neque et risus
  iaculis sodales sed eget diam. Quisque sodales nunc sapien, vitae lacinia ex
  luctus quis. Maecenas scelerisque scelerisque elit eu consequat. Etiam ac
  tristique tellus, sed tincidunt velit.
</p>

<p>
  Fusce dictum ex quis ipsum consectetur placerat. Cras sed lectus ex. Quisque
  purus dolor, vulputate ac mi eget, commodo varius odio. Suspendisse faucibus
  ipsum vel libero finibus, in placerat nibh congue. Sed iaculis, metus et
  euismod posuere, mi diam vestibulum felis, ac vulputate eros ipsum id justo.
  Etiam a tincidunt purus. Maecenas semper sed enim at blandit. Aenean ut
  sagittis lorem, eget gravida purus. Phasellus eleifend, lectus nec pulvinar
  facilisis, dui dolor feugiat odio, iaculis tempor felis est non tortor. In
  suscipit lorem efficitur molestie tempus. Integer sit amet neque et risus
  iaculis sodales sed eget diam. Quisque sodales nunc sapien, vitae lacinia ex
  luctus quis. Maecenas scelerisque scelerisque elit eu consequat. Etiam ac
  tristique tellus, sed tincidunt velit.
</p>

<div class="trigger">I create the trigger</div>

<p>
  Fusce dictum ex quis ipsum consectetur placerat. Cras sed lectus ex. Quisque
  purus dolor, vulputate ac mi eget, commodo varius odio. Suspendisse faucibus
  ipsum vel libero finibus, in placerat nibh congue. Sed iaculis, metus et
  euismod posuere, mi diam vestibulum felis, ac vulputate eros ipsum id justo.
  Etiam a tincidunt purus. Maecenas semper sed enim at blandit. Aenean ut
  sagittis lorem, eget gravida purus. Phasellus eleifend, lectus nec pulvinar
  facilisis, dui dolor feugiat odio, iaculis tempor felis est non tortor. In
  suscipit lorem efficitur molestie tempus. Integer sit amet neque et risus
  iaculis sodales sed eget diam. Quisque sodales nunc sapien, vitae lacinia ex
  luctus quis. Maecenas scelerisque scelerisque elit eu consequat. Etiam ac
  tristique tellus, sed tincidunt velit.
</p>

<p>
  Fusce dictum ex quis ipsum consectetur placerat. Cras sed lectus ex. Quisque
  purus dolor, vulputate ac mi eget, commodo varius odio. Suspendisse faucibus
  ipsum vel libero finibus, in placerat nibh congue. Sed iaculis, metus et
  euismod posuere, mi diam vestibulum felis, ac vulputate eros ipsum id justo.
  Etiam a tincidunt purus. Maecenas semper sed enim at blandit. Aenean ut
  sagittis lorem, eget gravida purus. Phasellus eleifend, lectus nec pulvinar
  facilisis, dui dolor feugiat odio, iaculis tempor felis est non tortor. In
  suscipit lorem efficitur molestie tempus. Integer sit amet neque et risus
  iaculis sodales sed eget diam. Quisque sodales nunc sapien, vitae lacinia ex
  luctus quis. Maecenas scelerisque scelerisque elit eu consequat. Etiam ac
  tristique tellus, sed tincidunt velit.
</p>

CSS

The .animated <div> element has an animation applied that rotates it. We set an animation-trigger value on it that references a trigger name of --t; we also specify two <animation-action> values — play and pause — which specify that the animation will play on activation, and pause on deactivation.

The .trigger <div> element creates the animated <div>'s trigger using:

A timeline-trigger-name value of --t, which is equal to the identifier referenced in the animated <div>'s animation-trigger property value, associating the two together.
A timeline-trigger-source value of view(), which sets the timeline trigger as a view progress timeline, and the element providing the timeline trigger as the nearest scrolling ancestor element.
A timeline-trigger-activation-range-start of entry 50%, which sets the trigger's activation range start point to 50% through the entry range (when 50% of the tracked element has entered the viewport). The timeline-trigger-activation-range-end value defaults to 100% of the way through the cover range, meaning that the animation won't pause until the tracked element has left the viewport in either direction.

body {
  width: 80%;
  margin: 0 auto;
  font-family: Arial, Helvetica, sans-serif;
  font-size: 1.3rem;
}

div {
  height: 100px;
  border: 5px solid black;
}

.animated {
  width: 100px;
  background: orange;
}

.trigger {
  background: wheat;
}

@supports not (timeline-trigger-name: --t) {
  body::before {
    font-family: sans-serif;
    font-size: 1.3rem;
    content: "Your browser does not support scroll-triggered animations.";
    background-color: wheat;
    position: fixed;
    left: 0;
    right: 0;
    top: 40%;
    text-align: center;
    padding: 1rem 0;
    z-index: 1;
  }
}

css

div.animated {
  animation: rotate 3s infinite linear both;
  animation-trigger: --t play pause;
}

div.trigger {
  timeline-trigger-name: --t;
  timeline-trigger-source: view();
  timeline-trigger-activation-range-start: entry 50%;
}

Next, we give the animated <div> a position of fixed, positioning it near the top-left of the viewport so that we can easily see when its animation starts and stops.

css

div.animated {
  position: fixed;
  top: 25px;
  left: 25px;
}

Finally, we define the @keyframes for the rotate animation:

css

@keyframes rotate {
  from {
    rotate: 0deg;
  }

  to {
    rotate: 360deg;
  }
}

Result

The rendered result looks like this:

Try scrolling the content up. When 50% of the tracked <div> has entered the viewport, the animation will play; when the tracked <div> has completely exited the viewport at either edge, the animation will pause.

Specifications

This feature does not appear to be defined in any specification.

Browser compatibility

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