/* 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"; this.EXPORTED_SYMBOLS = ["ScrollbarSampler"]; const {classes: Cc, interfaces: Ci, utils: Cu, results: Cr} = Components; Cu.import("resource://gre/modules/Services.jsm"); Cu.import("resource://gre/modules/XPCOMUtils.jsm"); var gSystemScrollbarWidth = null; this.ScrollbarSampler = { getSystemScrollbarWidth: function() { if (gSystemScrollbarWidth !== null) { return Promise.resolve(gSystemScrollbarWidth); } return new Promise(resolve => { this._sampleSystemScrollbarWidth().then(function(systemScrollbarWidth) { gSystemScrollbarWidth = systemScrollbarWidth; resolve(gSystemScrollbarWidth); }); }); }, resetSystemScrollbarWidth: function() { gSystemScrollbarWidth = null; }, _sampleSystemScrollbarWidth: function() { let hwin = Services.appShell.hiddenDOMWindow; let hdoc = hwin.document.documentElement; let iframe = hwin.document.createElementNS("http://www.w3.org/1999/xhtml", "html:iframe"); iframe.setAttribute("srcdoc", ''); hdoc.appendChild(iframe); let cwindow = iframe.contentWindow; let utils = cwindow.QueryInterface(Ci.nsIInterfaceRequestor) .getInterface(Ci.nsIDOMWindowUtils); return new Promise(resolve => { cwindow.addEventListener("load", function onLoad(aEvent) { cwindow.removeEventListener("load", onLoad); let sbWidth = {}; try { utils.getScrollbarSize(true, sbWidth, {}); } catch (e) { Cu.reportError("Could not sample scrollbar size: " + e + " -- " + e.stack); sbWidth.value = 0; } // Minimum width of 10 so that we have enough padding: sbWidth.value = Math.max(sbWidth.value, 10); resolve(sbWidth.value); iframe.remove(); }); }); } }; Object.freeze(this.ScrollbarSampler);