Bug 1557256 - handle scrollwheel zoom in reader mode, r=jaws

Differential Revision: https://phabricator.services.mozilla.com/D38069

--HG--
extra : moz-landing-system : lando

browser/base/content/browser-fullZoom.js

@@ -384,20 +384,16 @@ var FullZoom = {
       browser.messageManager.sendAsyncMessage("Reader:ResetZoom");
     } else if (this._isPDFViewer(browser)) {
       browser.messageManager.sendAsyncMessage("PDFJS:ZoomReset");
-    } else {
-      let token = this._getBrowserToken(browser);
-      let result = this._getGlobalValue(browser).then(value => {
-        if (token.isCurrent) {
-          ZoomManager.setZoomForBrowser(
-            browser,
-            value === undefined ? 1 : value
-          );
-          this._ignorePendingZoomAccesses(browser);
-        }
-      });
-      this._removePref(browser);
-      return result;
     }
+    let token = this._getBrowserToken(browser);
+    let result = this._getGlobalValue(browser).then(value => {
+      if (token.isCurrent) {
+        ZoomManager.setZoomForBrowser(browser, value === undefined ? 1 : value);
+        this._ignorePendingZoomAccesses(browser);
+      }
+    });
+    this._removePref(browser);
+    return result;
   },
 
   /**

toolkit/components/reader/AboutReader.jsm

@@ -39,6 +39,11 @@ var gStrings = Services.strings.createBundle(
   "chrome://global/locale/aboutReader.properties"
 );
 
+const zoomOnCtrl =
+  Services.prefs.getIntPref("mousewheel.with_control.action", 3) == 3;
+const zoomOnMeta =
+  Services.prefs.getIntPref("mousewheel.with_meta.action", 1) == 3;
+
 const gIsFirefoxDesktop =
   Services.appinfo.ID == "{ec8030f7-c20a-464f-9b0e-13a3a9e97384}";
 
@@ -116,6 +121,7 @@ var AboutReader = function(mm, win, articlePromise) {
   win.addEventListener("pagehide", this);
   win.addEventListener("mozvisualscroll", this, { mozSystemGroup: true });
   win.addEventListener("resize", this);
+  win.addEventListener("wheel", this, { passive: false });
 
   Services.obs.addObserver(this, "inner-window-destroyed");
 
@@ -414,6 +420,36 @@ AboutReader.prototype = {
         }
         break;
 
+      case "wheel":
+        let doZoom =
+          (aEvent.ctrlKey && zoomOnCtrl) || (aEvent.metaKey && zoomOnMeta);
+        if (!doZoom) {
+          return;
+        }
+        aEvent.preventDefault();
+
+        // Throttle events to once per 150ms. This avoids excessively fast zooming.
+        if (aEvent.timeStamp <= this._zoomBackoffTime) {
+          return;
+        }
+        this._zoomBackoffTime = aEvent.timeStamp + 150;
+
+        // Determine the direction of the delta (we don't care about its size);
+        // This code is adapted from normalizeWheelEventDelta in
+        // browser/extensions/pdfjs/content/web/viewer.js
+        let delta = Math.abs(aEvent.deltaX) + Math.abs(aEvent.deltaY);
+        let angle = Math.atan2(aEvent.deltaY, aEvent.deltaX);
+        if (-0.25 * Math.PI < angle && angle < 0.75 * Math.PI) {
+          delta = -delta;
+        }
+
+        if (delta > 0) {
+          this._changeFontSize(+1);
+        } else if (delta < 0) {
+          this._changeFontSize(-1);
+        }
+        break;
+
       case "devicelight":
         this._handleDeviceLight(aEvent.value);
         break;