Stop firing orientationchange events at pages that are not visible

Source/modules/screen_orientation/ScreenOrientationController.cpp

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "config.h"
 #include "modules/screen_orientation/ScreenOrientationController.h"
 
 #include "core/dom/Document.h"
 #include "core/events/Event.h"
 #include "core/frame/DOMWindow.h"
 #include "core/frame/FrameView.h"
 #include "core/frame/LocalFrame.h"
 #include "core/frame/Screen.h"
+#include "core/page/Page.h"
 #include "platform/LayoutTestSupport.h"
 #include "platform/PlatformScreen.h"
 
 namespace WebCore {
 
 ScreenOrientationController::~ScreenOrientationController()
 {
 }
 
 ScreenOrientationController& ScreenOrientationController::from(Document& document)
 {
     ScreenOrientationController* controller = static_cast<ScreenOrientationController*>(DocumentSupplement::from(document, supplementName()));
     if (!controller) {
         controller = new ScreenOrientationController(document);
         DocumentSupplement::provideTo(document, supplementName(), adoptPtrWillBeNoop(controller));
     }
     return *controller;
 }
 
 ScreenOrientationController::ScreenOrientationController(Document& document)
-    : m_document(document)
+    : PageLifecycleObserver(document.page())

[mlamouri (slow - plz ping), 2014/05/28 14:05:33]

Can a document get detached and attached again?

[Inactive, 2014/05/28 15:27:28]

I do not think so.

+    , m_document(document)
+    , m_lastVisibleOrientation(blink::WebScreenOrientationUndefined)
 {
 }
 
 const char* ScreenOrientationController::supplementName()
 {
     return "ScreenOrientationController";
 }
 
 // Compute the screen orientation using the orientation angle and the screen width / height.
 blink::WebScreenOrientationType ScreenOrientationController::computeOrientation(FrameView* view)
@@ skipping 15 matching lines @@
     case 180:
         return isTallDisplay ? blink::WebScreenOrientationPortraitSecondary : blink::WebScreenOrientationLandscapeSecondary;
     case 270:
         return isTallDisplay ? blink::WebScreenOrientationLandscapeSecondary : blink::WebScreenOrientationPortraitPrimary;
     default:
         ASSERT_NOT_REACHED();
         return blink::WebScreenOrientationPortraitPrimary;
     }
 }
 
+void ScreenOrientationController::pageVisibilityChanged()
+{
+    if (page() && page()->visibilityState() == PageVisibilityStateVisible) {
+        m_lastVisibleOrientation = blink::WebScreenOrientationUndefined;

[mlamouri (slow - plz ping), 2014/05/28 14:05:33]

I think it would be appropriate to also fire an event. As far as the web page is
concerned, this is a change in orientation.

[Inactive, 2014/05/28 15:27:28]

Done.

+    } else if (m_lastVisibleOrientation == blink::WebScreenOrientationUndefined) {
+        // The page is no longer visible, store the last know screen orientation
+        // so that we keep returning this orientation until the page becomes
+        // visible again.
+        m_lastVisibleOrientation = orientation();
+    }
+}
+
 blink::WebScreenOrientationType ScreenOrientationController::orientation() const
 {
+    if (m_lastVisibleOrientation != blink::WebScreenOrientationUndefined) {

[mlamouri (slow - plz ping), 2014/05/28 14:05:33]

I'm not a big fan of side effects like that (ie. m_lastVisibleOrientation is
used as the orientation to use when the page is hidden but also to know if the
page is hidden). I would prefer to be explicit and have something like:
if (!page() || page()->visibilityState() != PageVisibilityStateVisible) {
  return m_lastVisibleOrientation;
}

Then, you could do m_lastVisibleOrientation = orientationType later in that
function.

Speed wise, it should be fairly similar, clarity wise I prefer to be explicit
but it's up to you. Though, if you keep m_lastVisibleOrientation as is, could
you consider renaming it as suggested above?

[Inactive, 2014/05/28 15:27:28]

I renamed the variable to m_overrideOrientation for clarity.
The reason I am not sure about using the check you suggest is that I am worried
it is possible initially that the page is not yet visible and
m_overrideOrientation is still undefined as we haven't changed visibility state.

I also added your check as an assertion to document that we are not visible.

+        // The page is not visible, keep returning the last known screen orientation.
+        return m_lastVisibleOrientation;
+    }
+
     LocalFrame* mainFrame = m_document.frame();
     if (!mainFrame)
         return blink::WebScreenOrientationPortraitPrimary;
     blink::WebScreenOrientationType orientationType = screenOrientationType(mainFrame->view());
     if (orientationType == blink::WebScreenOrientationUndefined) {
         // The embedder could not provide us with an orientation, deduce it ourselves.
         orientationType = computeOrientation(mainFrame->view());
     }
     ASSERT(orientationType != blink::WebScreenOrientationUndefined);
     return orientationType;
 }
 
 } // namespace WebCore