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elm-animation

Build Status

Animate Float values with control over their start and end values, duration, easing, and so on. For example, animate a panel's width from 100px to 300px over 2 seconds, or make a button spin and grow on hover. Supports advanced features like smoothly retargeting to a new destination while in flight.

This library is fairly low-level from the perspective of building web apps. Many users will be better served by mdgriffith/elm-style-animation.

See more end-to-end example code in the examples/ folder.

Design Goals

The library encapsulates a 3-stage animation pipeline:

  • Timekeeping: Creating and running an animation requires the current time, which is best obtained by summing Browser.Events.onAnimationFrame. You can also specify the duration of animation, and delay it prior to starting.

  • Easing: An easing function makes an animation come alive with acceleration or even elasticity. You can find all kinds of crazy easing functions in this library.

  • Interpolation: It wouldn't be very useful is all animations went from 0 to 1 (the default), would it? You can specify values to animate from and to. Furthermore, you can set the average speed (distance between these two values per milisecond) instead of a duration.

Because the output of this library is a Float, you can use it with Html, Svg, or any other frontend.

Overview

animation creates an animation starting at the given time (usually the current time). animate takes the current time and an animation, and produces the current value. Animations go through three phases: they are scheduled, they run, and then they are done.

import Animation exposing (..)
import Time

myAnim : Animation
myAnim = animation 0
  |> from 100
  |> to 300
  |> duration 4
  |> delay 1

List.map (\t -> animate t myAnim) [0, 1, 2, 3, 4, 5, 6]
--> [100, 100, 129.28932188134524, 200, 270.71067811865476, 300, 300]

Notice that the value remains constant during the delay and after the animation is done. You can also use static to create animations of constant value. By using these two degenerate cases, you ought to be able to keep animations in your model without worrying about when they aren't actually animating.