Canvas Prototype: Trim

HTMLCanvasElement.prototype.trim.js

HTMLCanvasElement.prototype.trim = function () {
	var
	canvas = this,
	width = canvas.width,
	height = canvas.height,
	pixels = width * height,
	context = canvas.getContext('2d'),
	imageData = context.getImageData(0, 0, width, height),
	canvasPixelArray = imageData.data,
	top = height,
	right = 0,
	bottom = 0,
	left = width,
	i = 0,
	row;

	for (; i < pixels; ++i) {
		if (canvasPixelArray[i * 4] > 0) {
			row = Math.floor(i / height);

			top = Math.min(top, row);
			right = Math.max(right, i % width);
			bottom = Math.max(bottom, row);
			left = Math.min(left, i % width);
		}
	}

	canvas.width = right - left;
	canvas.height = bottom - top;

	context.putImageData(imageData, 0 - left, 0 - top);

	return this;
};