A simple canvas warp deformation in JavaScript. A graphics effects doing "pinch and rotate" of the canvas. All the basic control parameters are available. Combine with animations to do cool effects. Here are some live demos and more documentation.

You will need two canvas elements, an input one, and viewport one. viewport should probably be smaller than input since you will want to have enough room around for the effect to grab the pixels from (in case the warping stretches beyond the size of viewport).

Create a new Warp object providing it with those canvas elements, plus top and left coordinates for the viewport (i.e. where it is virtually placed on the input canvas).

Draw your stuff on the input canvas, then call deform() supplying actual warping parameters: center, radius and angle.

// assuming you have jQuery
var warp = new Warp({
	input_canvas: $('#input_canvas').get(0),
	viewport_canvas: $('#viewport_canvas').get(0),
	top: 100,
	left: 100
});

warp.deform({
	center: {x: 100, y: 100},
	radius: 50,
	angle: 45
});

Additionally you can also provide the transformation function, which determines how the rotation angle changes with distance to the origin of deformation.

warp.deform({
	center: {x: 100, y: 100},
	radius: 50,
	angle: 90,
	func: function (d) { return 1 + Math.sin( (d + 2) * Math.PI / 2 ) }
});

The function takes one floating point argument from 0.0 to 1.0, being the distance from origin (0.0 is the center of warping, 1.0 the edge of it) and returns a value between 0.0 and 1.0 representing the relative angle of rotation at this distance (0.0 being no rotation at all, 1.0 being the full angle). That means you probably want a function f which satisfies the following conditions:

f(0) = 1 (meaning at the center of warping make full rotation)

f(1) = 0 (meaning at the edge of warping make no rotation at all)

Here are a few example custom functions you can use. Refer to my blog post about this effect for a more visual explanation of custom functions: http://www.tinkeringwithstuff.com/posts/canvas-warping-with-javascript.html

• Just rotate by angle. That will look like a cut-out since every pixel inside the radius will be rotated by the same angle, irrespective of its distance to the center of deformation:

  function(d) {
      return 1;
  }

• Linear. This will linearly "interpolate" the rotation angle from no rotation at the edge to full rotation in the origin. That's the default if you don't provide a custom function and looks like a basic warp:

  function(d) {
      return 1.0 - d;
  }

• Sine. Smooth start and smooth end, like an S-shaped curve:

  function(d) {
      return 0.5 + Math.sin( (d + 0.5) * Math.PI ) / 2;
  }

• Sine 2. Smooth and slow start, sharp end:

  function(d) {
      return 1 + Math.sin( (d + 2) * Math.PI / 2 );
  }

Do-whatever-you-want-with-it license.