image-vectorizer/lib/types/Bitmap.js

Potrace in Javascript, for NodeJS and Browser

import Point from "./Point.js"
import utils from "../utils.js"
import Histogram from "./Histogram.js"

/**
 * Represents a bitmap where each pixel can be a number in range of 0..255
 * Used internally to store luminance data.
 *
 * @param {Number} w
 * @param {Number} h
 * @constructor
 */
function Bitmap(w, h) {
	this._histogram = null

	this.width = w
	this.height = h
	this.size = w * h
	this.arrayBuffer = new ArrayBuffer(this.size)
	this.data = new Uint8Array(this.arrayBuffer)
}

Bitmap.prototype = {
	/**
	 * Returns pixel value
	 *
	 * @param {Number|Point} x - index, point or x
	 * @param {Number} [y]
	 */
	getValueAt: function (x, y) {
		var index = typeof x === "number" && typeof y !== "number" ? x : this.pointToIndex(x, y)
		return this.data[index]
	},

	/**
	 * Converts {@link Point} to index value
	 *
	 * @param {Number} index
	 * @returns {Point}
	 */
	indexToPoint: function (index) {
		var point = new Point()

		if (utils.between(index, 0, this.size)) {
			point.y = Math.floor(index / this.width)
			point.x = index - point.y * this.width
		} else {
			point.x = -1
			point.y = -1
		}

		return point
	},

	/**
	 * Calculates index for point or coordinate pair
	 *
	 * @param {Number|Point} pointOrX
	 * @param {Number} [y]
	 * @returns {Number}
	 */
	pointToIndex: function (pointOrX, y) {
		var _x = pointOrX,
			_y = y

		if (pointOrX instanceof Point) {
			_x = pointOrX.x
			_y = pointOrX.y
		}

		if (!utils.between(_x, 0, this.width) || !utils.between(_y, 0, this.height)) {
			return -1
		}

		return this.width * _y + _x
	},

	/**
	 * Makes a copy of current bitmap
	 *
	 * @param {Function} [iterator] optional callback, used for processing pixel value. Accepted arguments: value, index
	 * @returns {Bitmap}
	 */
	copy: function (iterator) {
		var bm = new Bitmap(this.width, this.height),
			iteratorPresent = typeof iterator === "function",
			i

		for (i = 0; i < this.size; i++) {
			bm.data[i] = iteratorPresent ? iterator(this.data[i], i) : this.data[i]
		}

		return bm
	},

	histogram: function () {
		if (this._histogram) {
			return this._histogram
		}

		this._histogram = new Histogram(this)
		return this._histogram
	}
}

export default Bitmap