1 files changed, 121 insertions, 0 deletions
diff --git a/devtools/server/actors/highlighters/fonts.js b/devtools/server/actors/highlighters/fonts.js
new file mode 100644
index 0000000000..0fe6b066c7
--- /dev/null
+++ b/devtools/server/actors/highlighters/fonts.js
@@ -0,0 +1,121 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+"use strict";
+
+loader.lazyRequireGetter(
+  this,
+  "loadSheet",
+  "resource://devtools/shared/layout/utils.js",
+  true
+);
+loader.lazyRequireGetter(
+  this,
+  "removeSheet",
+  "resource://devtools/shared/layout/utils.js",
+  true
+);
+
+// How many text runs are we highlighting at a time. There may be many text runs, and we
+// want to prevent performance problems.
+const MAX_TEXT_RANGES = 100;
+
+// This stylesheet is inserted into the page to customize the color of the selected text
+// runs.
+// Note that this color is defined as --highlighter-content-color in the highlighters.css
+// file, and corresponds to the box-model content color. We want to give it an opacity of
+// 0.6 here.
+const STYLESHEET_URI =
+  "data:text/css," +
+  encodeURIComponent(
+    "::selection{background-color:hsl(197,71%,73%,.6)!important;}"
+  );
+
+/**
+ * This highlighter highlights runs of text in the page that have been rendered given a
+ * certain font. The highlighting is done with window selection ranges, so no extra
+ * markup is being inserted into the content page.
+ */
+class FontsHighlighter {
+  constructor(highlighterEnv) {
+    this.env = highlighterEnv;
+  }
+
+  destroy() {
+    this.hide();
+    this.env = this.currentNode = null;
+  }
+
+  get currentNodeDocument() {
+    if (!this.currentNode) {
+      return this.env.document;
+    }
+
+    if (this.currentNode.nodeType === this.currentNode.DOCUMENT_NODE) {
+      return this.currentNode;
+    }
+
+    return this.currentNode.ownerDocument;
+  }
+
+  /**
+   * Show the highlighter for a given node.
+   * @param {DOMNode} node The node in which we want to search for text runs.
+   * @param {Object} options A bunch of options that can be set:
+   * - {String} name The actual font name to look for in the node.
+   * - {String} CSSFamilyName The CSS font-family name given to this font.
+   */
+  show(node, options) {
+    this.currentNode = node;
+    const doc = this.currentNodeDocument;
+
+    // Get all of the fonts used to render content inside the node.
+    const searchRange = doc.createRange();
+    searchRange.selectNodeContents(node);
+
+    const fonts = InspectorUtils.getUsedFontFaces(searchRange, MAX_TEXT_RANGES);
+
+    // Find the ones we want, based on the provided option.
+    const matchingFonts = fonts.filter(
+      f => f.CSSFamilyName === options.CSSFamilyName && f.name === options.name
+    );
+    if (!matchingFonts.length) {
+      return;
+    }
+
+    // Load the stylesheet that will customize the color of the highlighter (using a
+    // ::selection rule).
+    loadSheet(this.env.window, STYLESHEET_URI);
+
+    // Create a multi-selection in the page to highlight the text runs.
+    const selection = doc.defaultView.getSelection();
+    selection.removeAllRanges();
+
+    for (const matchingFont of matchingFonts) {
+      for (const range of matchingFont.ranges) {
+        selection.addRange(range);
+      }
+    }
+  }
+
+  hide() {
+    // No node was highlighted before, don't need to continue any further.
+    if (!this.currentNode) {
+      return;
+    }
+
+    try {
+      removeSheet(this.env.window, STYLESHEET_URI);
+    } catch (e) {
+      // Silently fail here as we might not have inserted the stylesheet at all.
+    }
+
+    // Simply remove all current ranges in the seletion.
+    const doc = this.currentNodeDocument;
+    const selection = doc.defaultView.getSelection();
+    selection.removeAllRanges();
+  }
+}
+
+exports.FontsHighlighter = FontsHighlighter;