# KeyFrames

Manages key frame animation data. Associates time points with arbitrary data and provides methods to access key times and data, and an interpolation factor, based on the current time.


## Usage

```js
const keyFrames = new KeyFrames([
  [0, { val1: [1, 0, 1], val2: 0} ],
  [500, { val1: [1, 1, 1], val2: 2} ],
  [800, { val1: [0, 0, 1], val2: 1} ],
  [1200, { val1: [0, 1, 0], val2: 4} ],
  [1500, { val1: [1, 0, 1], val2: 5} ]
]);

keyFrames.setTime(1000);

keyFrames.startIndex;      // => 2                            (i.e. key frame at time=800)
keyFrames.endIndex;        // => 3                            (i.e. key frame at time=1200)
keyFrames.factor;          // => 0.5                          (i.e. halfway between 800 and 1200)
keyFrames.getStartTime();  // => 800                          (i.e. time at index 2)
keyFrames.getEndTime();    // => 1200                         (i.e. time at index 3)
keyFrames.getStartData();  // => { val1: [0, 0, 1], val2: 1}  (i.e. data at index 2)
keyFrames.getEndData();    // => { val1: [0, 1, 0], val2: 4}  (i.e. data at index 3)

```

## Properties
- `startIndex` (Number): Current start key frame index (i.e. the index of the key frame being interpolated from).
- `endIndex` (Number): Current end key frame index (i.e. the index of the key frame being interpolated to).
- `factor` (Number): A value between 0 and 1 representing the interpolation factor between the start and end key frame pair.

## Methods

### constructor(keyFrameData: Array)

Takes an array of `[time, data]` pairs to initialize the key frames.


### setKeyFrames(keyFrameData: Array)

Replaces the current set of key frames with a new one. Takes the same argument as the constructor.


### getStartTime() : Number

Returns the time at the current start key frame index.


### getEndTime() : Number

Returns the time at the current end key frame index.


### getStartData() : Any

Returns the data at the current start key frame index (i.e. the data being interpolated from).


### getEndData() : Any

Returns the data at the current end key frame index (i.e. the data being interpolated to).


### setTime(time: Number)

Set the current time of the key frames.