Bezier Curve functions in a handy CommonJS module (npm/browserify style).

Supports Linear, Quadratic and Cubic Bezier curves. By default curves are Cubic.

Also supports 'Find the value of Y at X(t)' functionality via an optionally built lookup table of a configurable number of samples. Used in this way it is advisable to precompute your curves and store them for later use rather than generating from scratch each time.

Browserify/NPM

    $ npm install --save gm-bezier

  var bezier = require('gm-bezier');

var Bezier = require('bezier').Bezier;

// create a default zeroed curve.
var curve = new Bezier();

Create a new Bezier Curve.

// create a curve initialised with a config object
var curve = new Bezier({ c1 : c1, c2 : c2, c3: c3, c4: c4 });

curve.c1( coords )

Set C1. C1 is the start point of the curve.

coords can come in the form { top: number, left : number} or { x : number, y : number} or [number, number]`

curve.c2( coords )

Set C2. C2 is the first control point.

coords can come in the form { top: number, left : number} or { x : number, y : number} or [number, number]`

curve.c3( coords )

Set C3. C3 is the second control point.

coords can come in the form { top: number, left : number} or { x : number, y : number} or [number, number]`

curve.c4( coords )

Set C4. C4 is the end point of the curve.

coords can come in the form { top: number, left : number} or { x : number, y : number} or [number, number]`

curve.buildLookup() // builds a lookup table of 1000 samples
curve.buildLookup(100) // builds a 100 sample lookup table

Iterates through the curve recording the value of X and Y. This allows you to then attempt to get the approximate value of Y for any particular value of X.

curve
  .buildLookup()
  .findYAtX(0.5) // === 0.334453

Find the approximate value of y = x(t). The more samples in the lookup table, the greater the accuracy and more CPU intensive it becomes to match.

curve.point( percent ) 

percent being a floating point number between 0 and 1, representing the start and end of the curve. Returns an object: {x : val, y: val}.

curve.pointArray( percent )

percent being a floating point number between 0 and 1, representing the start and end of the curve. Returns an array: [x, y].

curve.pointCss( percent )

percent being a floating point number between 0 and 1, representing the start and end of the curve. Returns an object: { top: val, left: val}.

curve
  .isCubic()
  .c1( c1 )
  .c2( c2 )
  .c3( c3 )
  .c4( c4 )

Explicitly sets the curve back to Cubic. This is the default, though. Doesn't need calling.

curve
  .isLinear()
  .c1([10,10])
  .c2([20,20])

Linear 'curve' mode - a straight line from C1 to C2.

curve
  .isQuadratic()
  .c1( c1 )
  .c2( c2 )
  .c3( c3 )

Quadratic curve mode. Only three control points required.

test/testrunner.html can be opened in a local browser assuming you have installed the npm deps.

    npm install
    grunt test

MIT