CanvasTextWrapper/js/CanvasTextWrapper.js

(function (root) {

	function CanvasTextWrapper(canvas, text, options) {
		'use strict';

		var defaults = {
			font: '18px Arial, sans-serif',
			sizeToFill: false,      // text is resized to fill the container (given font size is ignored)
			lineHeight: 1,          // default line height equivalent of '100%'
			allowNewLine: true,     // breaks text on every new line character '\n'
			lineBreak: 'auto',      // text fills the element's (canvas or parent) width going to a new line on a whole word
			textAlign: 'left',      // each line of text is aligned left
			verticalAlign: 'top',   // text lines block is aligned top
			justifyLines: false,    // lines are not justified
			paddingX: 0,            // 0px left & right text padding relatively to canvas or its container
			paddingY: 0,            // 0px top & bottom text padding relatively to canvas or its container
			fitParent: false,       // text is set to fit canvas width
			strokeText: false       // text is stroked according to context configuration
		};

		var opts = {};

		for (var property in defaults) {
			if (defaults.hasOwnProperty(property)) {
				opts[property] = (options && options[property]) ? options[property] : defaults[property];
			}
		}

		var context = canvas.getContext('2d');
		context.font = opts.font;
		context.textBaseline = 'bottom';

		var EL_WIDTH = (opts.fitParent === false) ? canvas.width : canvas.parentNode.clientWidth;
		var EL_HEIGHT = (opts.fitParent === false) ? canvas.height : canvas.parentNode.clientHeight;
		var MAX_TXT_WIDTH = EL_WIDTH - (opts.paddingX * 2);
		var MAX_TXT_HEIGHT = EL_HEIGHT - (opts.paddingY * 2);

		var fontSize, textBlockHeight, lines, newLineIndexes, textPos, lineHeight;

		init();

		function init() {
			fontSize = opts.font.match(/\d+(px|em|%)/g) ? +opts.font.match(/\d+(px|em|%)/g)[0].match(/\d+/g) : 18;

			textBlockHeight = 0;
			lines = [];
			newLineIndexes = [];
			textPos = {x: 0, y: 0};

			setFont(fontSize);
			setLineHeight();
			validate();
			render();
		}

		function render() {
			if (opts.sizeToFill) {
				var numWords = text.trim().split(/\s+/).length;
				var fontSize = 0;

				do {
					setFont(++fontSize);
					lineHeight = fontSize;
					wrap();
				} while (textBlockHeight < MAX_TXT_HEIGHT && (lines.join(' ').split(/\s+/).length == numWords));

				setFont(--fontSize);
				lineHeight = fontSize;
				wrap();
			} else {
				wrap();
			}

			if (opts.justifyLines && opts.lineBreak === 'auto') {
				justify();
			}

			setVerticalAlign();
			drawText();
		}

		function setFont(fontSize) {
			var fontParts = (!opts.sizeToFill) ? opts.font.split(/\b\d+px\b/i) : context.font.split(/\b\d+px\b/i);
			context.font = fontParts[0] + fontSize + 'px' + fontParts[1];
		}

		function setLineHeight() {
			if (!isNaN(opts.lineHeight)) {
				lineHeight = fontSize * opts.lineHeight;
			} else if (opts.lineHeight.toString().indexOf('px') !== -1) {
				lineHeight = parseInt(opts.lineHeight);
			} else if (opts.lineHeight.toString().indexOf('%') !== -1) {
				lineHeight = (parseInt(opts.lineHeight) / 100) * fontSize;
			}
		}

		function wrap() {
			if (opts.allowNewLine) {
				var newLines = text.trim().split('\n');
				for (var i = 0, idx = 0; i < newLines.length - 1; i++) {
					idx += newLines[i].trim().split(/\s+/).length;
					newLineIndexes.push(idx)
				}
			}

			var words = text.trim().split(/\s+/);
			checkLength(words);
			breakText(words);

			textBlockHeight = lines.length * lineHeight;
		}

		function checkLength(words) {
			var testString, tokenLen, sliced, leftover;

			for (var i = 0; i < words.length; i++) {
				testString = '';
				tokenLen = context.measureText(words[i]).width;

				if (tokenLen > MAX_TXT_WIDTH) {
					for (var k = 0; (context.measureText(testString + words[i][k]).width <= MAX_TXT_WIDTH) && (k < words[i].length); k++) {
						testString += words[i][k];
					}

					sliced = words[i].slice(0, k);
					leftover = words[i].slice(k);
					words.splice(i, 1, sliced, leftover);
				}
			}
		}

		function breakText(words) {
			for (var i = 0, j = 0; i < words.length; j++) {
				lines[j] = '';

				if (opts.lineBreak === 'auto') {
					while ((context.measureText(lines[j] + words[i]).width <= MAX_TXT_WIDTH) && (i < words.length)) {

						lines[j] += words[i] + ' ';
						i++;

						if (opts.allowNewLine) {
							for (var k = 0; k < newLineIndexes.length; k++) {
								if (newLineIndexes[k] === i) {
									j++;
									lines[j] = '';
									break;
								}
							}
						}
					}
					lines[j] = lines[j].trim();
				} else {
					lines[j] = words[i];
					i++;
				}
			}
		}

		function justify() {
			var maxLen, longestLineIndex, tokenLen;
			for (var i = 0; i < lines.length; i++) {
				tokenLen = context.measureText(lines[i]).width;

				if (!maxLen || tokenLen > maxLen) {
					maxLen = tokenLen;
					longestLineIndex = i;
				}
			}

			// fill lines with extra spaces
			var numWords, spaceLength, numOfSpaces, num, filler;
			var delimiter = '\u200A';
			for (i = 0; i < lines.length; i++) {
				if (i === longestLineIndex) continue;

				numWords = lines[i].trim().split(/\s+/).length;
				if (numWords <= 1) continue;

				lines[i] = lines[i].trim().split(/\s+/).join(delimiter);

				spaceLength = context.measureText(delimiter).width;
				numOfSpaces = (maxLen - context.measureText(lines[i]).width) / spaceLength;
				num = numOfSpaces / (numWords - 1);

				filler = '';
				for (var j = 0; j < num; j++) {
					filler += delimiter;
				}

				lines[i] = lines[i].trim().split(delimiter).join(filler);
				//console.log('numWords:', numWords, 'numOfSpaces:', numOfSpaces, 'num:', num);
			}
		}

		function drawText() {
			for (var i = 0; i < lines.length; i++) {
				setHorizontalAlign(lines[i]);

				textPos.y = parseInt(textPos.y) + lineHeight;
				context.fillText(lines[i], textPos.x, textPos.y);

				if (opts.strokeText) {
					context.strokeText(lines[i], textPos.x, textPos.y);
				}
			}
		}

		function setHorizontalAlign(line) {
			if (opts.textAlign == 'center') {
				textPos.x = (EL_WIDTH - context.measureText(line).width) / 2;
			} else if (opts.textAlign == 'right') {
				textPos.x = EL_WIDTH - context.measureText(line).width - opts.paddingX;
			} else {
				textPos.x = opts.paddingX;
			}
		}

		function setVerticalAlign() {
			if (opts.verticalAlign == 'middle') {
				textPos.y = (EL_HEIGHT - textBlockHeight) / 2;
			} else if (opts.verticalAlign == 'bottom') {
				textPos.y = EL_HEIGHT - textBlockHeight - opts.paddingY;
			} else {
				textPos.y = opts.paddingY;
			}
		}

		function validate() {
			if (!(canvas instanceof HTMLCanvasElement))
				throw new TypeError('The first parameter must be an instance of HTMLCanvasElement.');

			if (typeof text !== 'string')
				throw new TypeError('The second parameter must be a string.');

			if (isNaN(fontSize))
				throw new TypeError('Cannot parse "font".');

			if (isNaN(lineHeight))
				throw new TypeError('Cannot parse "lineHeight".');

			if (opts.textAlign.toLocaleLowerCase() !== 'left' && opts.textAlign.toLocaleLowerCase() !== 'center' && opts.textAlign.toLocaleLowerCase() !== 'right')
				throw new TypeError('Property "textAlign" must be set to either "left", "center", or "right".');

			if (opts.verticalAlign.toLocaleLowerCase() !== 'top' && opts.verticalAlign.toLocaleLowerCase() !== 'middle' && opts.verticalAlign.toLocaleLowerCase() !== 'bottom')
				throw new TypeError('Property "verticalAlign" must be set to either "top", "middle", or "bottom".');

			if (typeof opts.justifyLines !== 'boolean')
				throw new TypeError('Property "justifyLines" must be set to a Boolean.');

			if (isNaN(opts.paddingX))
				throw new TypeError('Property "paddingX" must be set to a Number.');

			if (isNaN(opts.paddingY))
				throw new TypeError('Property "paddingY" must be set to a Number.');

			if (typeof opts.fitParent !== 'boolean')
				throw new TypeError('Property "fitParent" must be set to a Boolean.');

			if (opts.lineBreak.toLocaleLowerCase() !== 'auto' && opts.lineBreak.toLocaleLowerCase() !== 'word')
				throw new TypeError('Property "lineBreak" must be set to either "auto" or "word".');

			if (typeof opts.sizeToFill !== 'boolean')
				throw new TypeError('Property "sizeToFill" must be set to a Boolean.');

			if (typeof opts.strokeText !== 'boolean')
				throw new TypeError('Property "strokeText" must be set to a Boolean.');
		}
	}

	if ('module' in root && 'exports' in module) {
		module.exports = CanvasTextWrapper;
	} else {
		root.CanvasTextWrapper = CanvasTextWrapper;
	}
})(this);