Line Numbers: Improved resize performance

plugins/line-numbers/prism-line-numbers.js

@@ -16,17 +16,69 @@
 	 */
 	var NEW_LINE_EXP = /\n(?!$)/g;
 
+
+	/**
+	 * Global exports
+	 */
+	var config = Prism.plugins.lineNumbers = {
+		/**
+		 * Get node for provided line number
+		 * @param {Element} element pre element
+		 * @param {Number} number line number
+		 * @return {Element|undefined}
+		 */
+		getLine: function (element, number) {
+			if (element.tagName !== 'PRE' || !element.classList.contains(PLUGIN_NAME)) {
+				return;
+			}
+
+			var lineNumberRows = element.querySelector('.line-numbers-rows');
+			var lineNumberStart = parseInt(element.getAttribute('data-start'), 10) || 1;
+			var lineNumberEnd = lineNumberStart + (lineNumberRows.children.length - 1);
+
+			if (number < lineNumberStart) {
+				number = lineNumberStart;
+			}
+			if (number > lineNumberEnd) {
+				number = lineNumberEnd;
+			}
+
+			var lineIndex = number - lineNumberStart;
+
+			return lineNumberRows.children[lineIndex];
+		},
+
+		/**
+		 * Whether the plugin can assume that the units font sizes and margins are not depended on the size of
+		 * the current viewport.
+		 *
+		 * Setting this to `true` will allow the plugin to do certain optimizations for better performance.
+		 *
+		 * Set this to `false` if you use any of the following CSS units: `vh`, `vw`, `vmin`, `vmax`.
+		 *
+		 * @type {boolean}
+		 */
+		assumeViewportIndependence: false
+	};
+
 	/**
-	 * Resizes line numbers spans according to height of line of code
-	 * @param {Element} element <pre> element
+	 * Resizes the given elements.
+	 *
+	 * @param {HTMLElement[]} elements
 	 */
-	var _resizeElement = function (element) {
-		var codeStyles = getStyles(element);
-		var whiteSpace = codeStyles['white-space'];
+	function resizeElements(elements) {
+		elements = elements.filter(function (e) {
+			var codeStyles = getStyles(e);
+			var whiteSpace = codeStyles['white-space'];
+			return whiteSpace === 'pre-wrap' || whiteSpace === 'pre-line';
+		});
+
+		if (elements.length == 0) {
+			return;
+		}
 
-		if (whiteSpace === 'pre-wrap' || whiteSpace === 'pre-line') {
+		var infos = elements.map(function (element) {
 			var codeElement = element.querySelector('code');
-			var lineNumbersWrapper = element.querySelector('.line-numbers-rows');
 			var lineNumberSizer = element.querySelector('.line-numbers-sizer');
 			var codeLines = codeElement.textContent.split(NEW_LINE_EXP);
 
@@ -37,18 +89,63 @@
 				codeElement.appendChild(lineNumberSizer);
 			}
 
+			lineNumberSizer.innerHTML = '0';
 			lineNumberSizer.style.display = 'block';
 
-			codeLines.forEach(function (line, lineNumber) {
-				lineNumberSizer.textContent = line || '\n';
-				var lineSize = lineNumberSizer.getBoundingClientRect().height;
-				lineNumbersWrapper.children[lineNumber].style.height = lineSize + 'px';
+			var oneLinerHeight = lineNumberSizer.getBoundingClientRect().height;
+			lineNumberSizer.innerHTML = '';
+
+			return {
+				element: element,
+				lines: codeLines,
+				lineHeights: [],
+				oneLinerHeight: oneLinerHeight,
+				sizer: lineNumberSizer,
+			};
+		});
+
+		infos.forEach(function (info) {
+			var lineNumberSizer = info.sizer;
+			var lines = info.lines;
+			var lineHeights = info.lineHeights;
+			var oneLinerHeight = info.oneLinerHeight;
+
+			lineHeights[lines.length - 1] = undefined;
+			lines.forEach(function (line, index) {
+				if (line && line.length > 1) {
+					var e = lineNumberSizer.appendChild(document.createElement('span'));
+					e.style.display = 'block';
+					e.textContent = line;
+				} else {
+					lineHeights[index] = oneLinerHeight;
+				}
 			});
+		});
+
+		infos.forEach(function (info) {
+			var lineNumberSizer = info.sizer;
+			var lineHeights = info.lineHeights;
+
+			var childIndex = 0;
+			for (var i = 0; i < lineHeights.length; i++) {
+				if (lineHeights[i] === undefined) {
+					lineHeights[i] = lineNumberSizer.children[childIndex++].getBoundingClientRect().height;
+				}
+			}
+		});
+
+		infos.forEach(function (info) {
+			var lineNumberSizer = info.sizer;
+			var wrapper = info.element.querySelector('.line-numbers-rows');
 
-			lineNumberSizer.textContent = '';
 			lineNumberSizer.style.display = 'none';
-		}
-	};
+			lineNumberSizer.innerHTML = '';
+
+			info.lineHeights.forEach(function (height, lineNumber) {
+				wrapper.children[lineNumber].style.height = height + 'px';
+			});
+		});
+	}
 
 	/**
 	 * Returns style declarations for the element
@@ -62,8 +159,14 @@
 		return window.getComputedStyle ? getComputedStyle(element) : (element.currentStyle || null);
 	};
 
+	var lastWidth = undefined;
 	window.addEventListener('resize', function () {
-		Array.prototype.forEach.call(document.querySelectorAll('pre.' + PLUGIN_NAME), _resizeElement);
+		if (config.assumeViewportIndependence && lastWidth === window.innerWidth) {
+			return;
+		}
+		lastWidth = window.innerWidth;
+
+		resizeElements(Array.prototype.slice.call(document.querySelectorAll('pre.' + PLUGIN_NAME)));
 	});
 
 	Prism.hooks.add('complete', function (env) {
@@ -123,7 +226,7 @@
 
 		env.element.appendChild(lineNumbersWrapper);
 
-		_resizeElement(pre);
+		resizeElements([pre]);
 
 		Prism.hooks.run('line-numbers', env);
 	});
@@ -133,36 +236,4 @@
 		env.plugins.lineNumbers = true;
 	});
 
-	/**
-	 * Global exports
-	 */
-	Prism.plugins.lineNumbers = {
-		/**
-		 * Get node for provided line number
-		 * @param {Element} element pre element
-		 * @param {Number} number line number
-		 * @return {Element|undefined}
-		 */
-		getLine: function (element, number) {
-			if (element.tagName !== 'PRE' || !element.classList.contains(PLUGIN_NAME)) {
-				return;
-			}
-
-			var lineNumberRows = element.querySelector('.line-numbers-rows');
-			var lineNumberStart = parseInt(element.getAttribute('data-start'), 10) || 1;
-			var lineNumberEnd = lineNumberStart + (lineNumberRows.children.length - 1);
-
-			if (number < lineNumberStart) {
-				number = lineNumberStart;
-			}
-			if (number > lineNumberEnd) {
-				number = lineNumberEnd;
-			}
-
-			var lineIndex = number - lineNumberStart;
-
-			return lineNumberRows.children[lineIndex];
-		}
-	};
-
 }());