# Class: Hermite

## Phaser. Hermite

#### new Hermite(p1x, p1y, p2x, p2y, v1x, v1y, v2x, v2y [, accuracy])

A data representation of a Hermite Curve (see http://en.wikipedia.org/wiki/Cubic_Hermite_spline)

A Hermite curve has a start and end point and tangent vectors for both of them. The curve will always pass through the two control points and the shape of it is controlled by the length and direction of the tangent vectors. At the control points the curve will be facing exactly in the vector direction.

As these curves change speed (speed = distance between points separated by an equal change in 't' value - see Hermite.getPoint) this class attempts to reduce the variation by pre-calculating the `accuracy` number of points on the curve. The straight-line distances to these points are stored in the private 'points' array, and this information is used by Hermite.findT() to convert a pixel distance along the curve into a 'time' value.

Higher `accuracy` values will result in more even movement, but require more memory for the points list. 5 works, but 10 seems to be an ideal value for the length of curves found in most games on a desktop screen. If you use very long curves (more than 400 pixels) you may need to increase this value further.

##### Parameters:
Name Type Argument Default Description
`p1x` number

The x coordinate of the start of the curve.

`p1y` number

The y coordinate of the start of the curve.

`p2x` number

The x coordinate of the end of the curve.

`p2y` number

The y coordinate of the end of the curve.

`v1x` number

The x component of the tangent vector for the start of the curve.

`v1y` number

The y component of the tangent vector for the start of the curve.

`v2x` number

The x component of the tangent vector for the end of the curve.

`v2y` number

The y component of the tangent vector for the end of the curve.

`accuracy` number <optional>
10

The amount of points to pre-calculate on the curve.

Source:
src/geom/Hermite.js line 39

### Members

#### accuracy : number

The amount of points to pre-calculate on the curve.

##### Type:
• number
Source:
src/geom/Hermite.js line 385

#### p1x : number

The x coordinate of the start of the curve. Setting this value will recalculate the curve.

##### Type:
• number
Source:
src/geom/Hermite.js line 407

#### p1y : number

The y coordinate of the start of the curve. Setting this value will recalculate the curve.

##### Type:
• number
Source:
src/geom/Hermite.js line 429

#### p2x : number

The x coordinate of the end of the curve. Setting this value will recalculate the curve.

##### Type:
• number
Source:
src/geom/Hermite.js line 451

#### p2y : number

The y coordinate of the end of the curve. Setting this value will recalculate the curve.

##### Type:
• number
Source:
src/geom/Hermite.js line 473

#### v1x : number

The x component of the tangent vector for the start of the curve. Setting this value will recalculate the curve.

##### Type:
• number
Source:
src/geom/Hermite.js line 495

#### v1y : number

The y component of the tangent vector for the start of the curve. Setting this value will recalculate the curve.

##### Type:
• number
Source:
src/geom/Hermite.js line 517

#### v2x : number

The x component of the tangent vector for the end of the curve. Setting this value will recalculate the curve.

##### Type:
• number
Source:
src/geom/Hermite.js line 539

#### v2y : number

The y component of the tangent vector for the end of the curve. Setting this value will recalculate the curve.

##### Type:
• number
Source:
src/geom/Hermite.js line 561

### Methods

#### calculateEvenPoints()

Calculate a number of points along the curve, based on `Hermite.accuracy`, and stores them in the private `_points` array.

Source:
src/geom/Hermite.js line 144
##### Returns:

The total length of the curve approximated as straight line distances between the points.

Type
number

#### findT(distance)

Convert a distance along this curve into a `time` value which will be between 0 and 1.

For example if this curve has a length of 100 pixels then `findT(50)` would return `0.5`.

##### Parameters:
Name Type Description
`distance` integer

The distance into the curve in pixels. Should be a positive integer.

Source:
src/geom/Hermite.js line 170
##### Returns:

The time (`t`) value, a float between 0 and 1.

Type
number

#### getAngle( [t])

Calculate and return the angle, in radians, of the curves tangent based on time.

##### Parameters:
Name Type Argument Default Description
`t` number <optional>
0

The `t` (time) value at which to find the angle. Must be between 0 and 1.

Source:
src/geom/Hermite.js line 328
##### Returns:

The angle of the line at the specified `t` time value along the curve. The value is in radians.

Type
number

#### getAngleWithDistance( [distance])

Calculate and return the angle, in radians, of the curves tangent at the given pixel distance along the curves length.

##### Parameters:
Name Type Argument Default Description
`distance` number <optional>
0

The distance along the curve to get the angle from, in pixels.

Source:
src/geom/Hermite.js line 345
##### Returns:

The angle of the line at the specified distance along the curve. The value is in radians.

Type
number

#### getEntryTangent(point)

Get the angle of the curves entry point.

##### Parameters:
Name Type Description
`point` Phaser.Point | Object

The Phaser.Point object, or an Object with public `x` and `y` properties, in which the tangent vector values will be stored.

Source:
src/geom/Hermite.js line 366
##### Returns:

A Point object containing the tangent vector of this Hermite curve.

Type
Phaser.Point

#### getPoint( [t] [, point])

Get a point on the curve using the `t` (time) value, which must be between 0 and 1.

##### Parameters:
Name Type Argument Default Description
`t` number <optional>
0

The time value along the curve from which to extract a point. This is a value between 0 and 1, where 0 represents the start of the curve and 1 the end.

`point` Phaser.Point | Object <optional>

An optional Phaser.Point, or Object containing public `x` and `y` properties. If given the resulting values will be stored in the Objects `x` and `y` properties. If omitted a new Phaser.Point object is created.

Source:
src/geom/Hermite.js line 270
##### Returns:

An Object with the x, y coordinate of the curve at the specified `t` value set in its `x` and `y` properties.

Type
Phaser.Point

#### getPointWithDistance( [distance] [, point])

Get a point on the curve using the distance, in pixels, along the curve.

##### Parameters:
Name Type Argument Default Description
`distance` integer <optional>
0

The distance along the curve to get the point from, given in pixels.

`point` Phaser.Point | Object <optional>

An optional Phaser.Point, or Object containing public `x` and `y` properties. If given the resulting values will be stored in the Objects `x` and `y` properties. If omitted a new Phaser.Point object is created.

Source:
src/geom/Hermite.js line 302
##### Returns:

The point on the line at the specified 'distance' along the curve.

Type
Phaser.Point

#### getX( [t])

Get the X component of a point on the curve based on the `t` (time) value, which must be between 0 and 1.

##### Parameters:
Name Type Argument Default Description
`t` number <optional>
0

The time value along the curve from which to extract a point. This is a value between 0 and 1, where 0 represents the start of the curve and 1 the end.

Source:
src/geom/Hermite.js line 206
##### Returns:

The X component of a point on the curve based on the `t` (time) value.

Type
number

#### getY( [t])

Get the Y component of a point on the curve based on the `t` (time) value, which must be between 0 and 1.

##### Parameters:
Name Type Argument Default Description
`t` number <optional>
0

The time value along the curve from which to extract a point. This is a value between 0 and 1, where 0 represents the start of the curve and 1 the end.

Source:
src/geom/Hermite.js line 238
##### Returns:

The Y component of a point on the curve based on the `t` (time) value.

Type
number

#### recalculate()

Performs the curve calculations.

This is called automatically if you change any of the curves public properties, such as `Hermite.p1x` or `Hermite.v2y`.

If you adjust any of the internal private values, then call this to update the points.

Source:
src/geom/Hermite.js line 122

This object.

Type
Phaser.Hermite