1 files changed, 59 insertions, 0 deletions
diff --git a/toolkit/modules/LayoutUtils.sys.mjs b/toolkit/modules/LayoutUtils.sys.mjs
new file mode 100644
index 0000000000..f3f9d0582b
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+++ b/toolkit/modules/LayoutUtils.sys.mjs
@@ -0,0 +1,59 @@
+/* -*- mode: js; indent-tabs-mode: nil; js-indent-level: 2 -*- */
+/* 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/. */
+
+export var LayoutUtils = {
+  /**
+   * For a given DOM element, returns its position in screen coordinates of CSS units
+   * (<https://developer.mozilla.org/en-US/docs/Web/CSS/CSSOM_View/Coordinate_systems#screen>).
+   */
+  getElementBoundingScreenRect(aElement) {
+    let rect = aElement.getBoundingClientRect();
+    let win = aElement.ownerGlobal;
+
+    const { x, y, width, height } = this._rectToClientRect(win, rect);
+    return win.windowUtils.toScreenRectInCSSUnits(x, y, width, height);
+  },
+
+  /**
+   * Similar to getElementBoundingScreenRect using window and rect,
+   * returns screen coordinates in screen units.
+   */
+  rectToScreenRect(win, rect) {
+    const { x, y, width, height } = this._rectToClientRect(win, rect);
+    return win.ownerGlobal.windowUtils.toScreenRect(x, y, width, height);
+  },
+
+  _rectToClientRect(win, rect) {
+    let x = rect.left;
+    let y = rect.top;
+
+    // We need to compensate for ancestor iframes in the same process
+    // that might shift things over.
+    let parentFrame = win.browsingContext?.embedderElement;
+    while (parentFrame) {
+      win = parentFrame.ownerGlobal;
+      let cstyle = win.getComputedStyle(parentFrame);
+
+      let framerect = parentFrame.getBoundingClientRect();
+      x +=
+        framerect.left +
+        parseFloat(cstyle.borderLeftWidth) +
+        parseFloat(cstyle.paddingLeft);
+      y +=
+        framerect.top +
+        parseFloat(cstyle.borderTopWidth) +
+        parseFloat(cstyle.paddingTop);
+
+      parentFrame = win.browsingContext?.embedderElement;
+    }
+
+    return {
+      x,
+      y,
+      width: rect.width,
+      height: rect.height,
+    };
+  },
+};