owl/doc/animations.md

🦉 Animations 🦉

Animation is a complex topic. There are many different use cases, and many solutions and technologies. Owl only supports some basic use cases.

Simple CSS effects

Sometimes, using pure CSS is enough. For these use cases, Owl is not really necessary: it just needs to render a DOM element with a specific class. For example:

<a class="btn flash" t-on-click="doSomething">Click</a>

with the following CSS:

btn {
  background-color: gray;
}

.flash {
  transition: background 0.5s;
}

.flash:active {
  background-color: #41454a;
  transition: background 0s;
}

will produce a nice flash effect whenever the user click (or activate with the keyboard) the button.

CSS Transitions

A more complex situation occurs when we want to transition an element in or out of the page. For example, we may want a fade-in and fade-out effect.

The t-transition directive is here to help us (see QWeb documentation).

To perform useful transition effects, whenever an element appears or disappears, it is necessary to add/remove some css style or class at some precise moment in the lifetime of a node. Since this is not easy to do by hand, Owl t-transition directive is there to help.

Whenever a node has a t-transition directive, with a name value, the following will happen:

At node insertion:

• the css classes name-enter and name-enter-active will be added directly when the node is inserted into the DOM,
• on the next animation frame: the css class name-enter will be removed and the class name-enter-to will be added (so they can be used to trigger css transition effects),
• the css class name-enter-active will be removed whenever a css transition ends.

At node destruction:

• the css classes name-leave and name-leave-active will be added before the node is removed to the DOM,
• the css class name-leave will be removed on the next animation frame (so it can be used to trigger css transition effects),
• the css class name-leave-active will be removed whenever a css transition ends. Only then will the element be removed from the DOM.

For example, a simple fade in/out effect can be done with this:

<div>
    <div t-if="state.flag" class="square" t-transition="fade">Hello</div>
</div>

.fade-enter-active,
.fade-leave-active {
  transition: opacity 0.5s;
}
.fade-enter,
.fade-leave-to {
  opacity: 0;
}

The t-transition directive can be combined with t-widget.

Notes:

• more information on animations are available here.
• Owl does not support more than one transition on a single node, so the t-transition expression must be a single value (i.e. no space allowed)