Bug 309478 – [GTK][WPE][Coordinated Graphics] the page is flickering while transition to the previous page

• Component: WebKitGTK
• Status: NEW

[Fujii Hironori]

[GTK][WPE][Coordinated Graphics] the page is flickering while transition to the previous page

1. python -m http.server -d .
2. ./Tools/Scripts/run-minibrowser --wpe --release http://localhost:8000/LayoutTests/svg/as-image
3. Scroll down to the bottom of the page
4. Click the last item 'view-in-inner-svg.html'
5. Go back

I observe 3 issues.

While transition to the previous page, the page flickering
The bottom of the previous page aren't painted
A dark scroll bar is painted

[Fujii Hironori]

Created attachment 478608 [details]
test case

1. Load the test content
2. Click step 1
3. Click step 2
4. Back

There is no tiles. 
You can see the compsiting borders with --features=+CompositingBordersVisible .

[Fujii Hironori]

Tiles are missing because the coverage area are miscomputed by computeCoverAndKeepRect().
The layer position was inconsistent between CoordinatedPlatformLayer and GraphicsLayerCoordinate.
After the history back, CoordinatedPlatformLayer::setTopLeftPositionForScrolling() was called, but GraphicsLayerCoordinated::syncPosition() wasn't called yet.

[Fujii Hironori]

I checked Mac port.
GraphicsLayerCA::setPosition was called from HistoryController::restoreScrollPositionAndViewState with the following callstack.
Thus, the coverage area is correct.

1   0x119ac85d7 WebCore::GraphicsLayerCA::setPosition(WebCore::FloatPoint const&)
2   0x11a9192ef WebCore::AsyncScrollingCoordinator::reconcileScrollingState(WebCore::LocalFrameView&, WebCore::FloatPoint const&, mpark::variant<std::__1::optional<WebCore::FloatPoint>, std::__1::optional<WebCore::FloatRect>> const&, WebCore::ScrollType, WebCore::ViewportRectStability, WebCore::ScrollingLayerPositionAction) (.cold.2)
3   0x1198a804c WebCore::AsyncScrollingCoordinator::reconcileScrollingState(WebCore::LocalFrameView&, WebCore::FloatPoint const&, mpark::variant<std::__1::optional<WebCore::FloatPoint>, std::__1::optional<WebCore::FloatRect>> const&, WebCore::ScrollType, WebCore::ViewportRectStability, WebCore::ScrollingLayerPositionAction)
4   0x11a91766f WebCore::AsyncScrollingCoordinator::updateScrollPositionAfterAsyncScroll(WebCore::ProcessQualified<WTF::ObjectIdentifierGeneric<WebCore::ScrollingNodeIDType, WTF::ObjectIdentifierMainThreadAccessTraits<unsigned long long>, unsigned long long>>, WebCore::FloatPoint, std::__1::optional<WebCore::FloatPoint>, WebCore::ScrollingLayerPositionAction, WebCore::ScrollType, WebCore::ViewportRectStability)
5   0x1198a768e WebCore::AsyncScrollingCoordinator::applyScrollPositionUpdate(WebCore::ScrollUpdate&&, WebCore::ScrollType, WebCore::ViewportRectStability)
6   0x1198a7b0b WebCore::AsyncScrollingCoordinator::applyScrollUpdate(WebCore::ScrollUpdate&&, WebCore::ScrollType, WebCore::ViewportRectStability)
7   0x1198a6b9c WebCore::AsyncScrollingCoordinator::requestScrollToPosition(WebCore::ScrollableArea&, WebCore::IntPoint const&, WebCore::ScrollPositionChangeOptions const&)
8   0x11a8dd304 WebCore::LocalFrameView::requestScrollToPosition(WebCore::IntPoint const&, WebCore::ScrollPositionChangeOptions const&) (.cold.1)
9   0x119815340 WebCore::LocalFrameView::requestScrollToPosition(WebCore::IntPoint const&, WebCore::ScrollPositionChangeOptions const&)
10  0x119914f5e WebCore::ScrollView::setScrollPosition(WebCore::IntPoint const&, WebCore::ScrollPositionChangeOptions const&)
11  0x11a8d1e62 WebCore::LocalFrameView::setScrollOffsetWithOptions(WebCore::IntPoint const&, WebCore::ScrollPositionChangeOptions const&)
12  0x119805990 WebCore::LocalFrameView::setScrollPosition(WebCore::IntPoint const&, WebCore::ScrollPositionChangeOptions const&)
13  0x11983954a WebCore::Page::setPageScaleFactor(float, WebCore::IntPoint const&, bool)
14  0x11972c817 WebCore::HistoryController::restoreScrollPositionAndViewState()
15  0x11971330c WebCore::FrameLoader::checkLoadCompleteForThisFrame(WebCore::LoadWillContinueInAnotherProcess)
16  0x119708dc8 WebCore::FrameLoader::checkLoadComplete(WebCore::LoadWillContinueInAnotherProcess)
17  0x119708a48 WebCore::FrameLoader::checkCompleted()
18  0x11a859f48 WebCore::FrameLoader::commitProvisionalLoad()
19  0x11a85aa16 WebCore::FrameLoader::loadProvisionalItemFromCachedPage()
20  0x1197114f1 WebCore::FrameLoader::continueLoadAfterNavigationPolicy(WebCore::ResourceRequest const&, WebCore::FormSubmission const*, WebCore::NavigationPolicyDecision, WebCore::AllowNavigationToInvalidURL)
21  0x11972ae52 WTF::Detail::CallableWrapper<WebCore::FrameLoader::loadWithDocumentLoader(WebCore::DocumentLoader*, WebCore::FrameLoadType, WTF::RefPtr<WebCore::FormSubmission const, WTF::RawPtrTraits<WebCore::FormSubmission const>, WTF::DefaultRefDerefTraits<WebCore::FormSubmission const>>&&, WebCore::AllowNavigationToInvalidURL, WTF::CompletionHandler<void ()>&&)::$_1, void, WebCore::ResourceRequest&&, WTF::WeakPtr<WebCore::FormSubmission const, WTF::DefaultWeakPtrImpl, WTF::RawPtrTraits<WTF::DefaultWeakPtrImpl>>&&, WebCore::NavigationPolicyDecision>::call(WebCore::ResourceRequest&&, WTF::WeakPtr<WebCore::FormSubmission const, WTF::DefaultWeakPtrImpl, WTF::RawPtrTraits<WTF::DefaultWeakPtrImpl>>&&, WebCore::NavigationPolicyDecision)
22  0x11a876778 WTF::Detail::CallableWrapper<WebCore::PolicyChecker::checkNavigationPolicy(WebCore::ResourceRequest&&, WebCore::ResourceResponse const&, WebCore::DocumentLoader*, WTF::RefPtr<WebCore::FormSubmission const, WTF::RawPtrTraits<WebCore::FormSubmission const>, WTF::DefaultRefDerefTraits<WebCore::FormSubmission const>>&&, WTF::CompletionHandler<void (WebCore::ResourceRequest&&, WTF::WeakPtr<WebCore::FormSubmission const, WTF::DefaultWeakPtrImpl, WTF::RawPtrTraits<WTF::DefaultWeakPtrImpl>>&&, WebCore::NavigationPolicyDecision)>&&, WebCore::PolicyDecisionMode, std::__1::optional<WebCore::NavigationNavigationType>)::$_1, void, WebCore::PolicyAction>::call(WebCore::PolicyAction) (.cold.5)
23  0x119745968 WTF::Detail::CallableWrapper<WebCore::PolicyChecker::checkNavigationPolicy(WebCore::ResourceRequest&&, WebCore::ResourceResponse const&, WebCore::DocumentLoader*, WTF::RefPtr<WebCore::FormSubmission const, WTF::RawPtrTraits<WebCore::FormSubmission const>, WTF::DefaultRefDerefTraits<WebCore::FormSubmission const>>&&, WTF::CompletionHandler<void (WebCore::ResourceRequest&&, WTF::WeakPtr<WebCore::FormSubmission const, WTF::DefaultWeakPtrImpl, WTF::RawPtrTraits<WTF::DefaultWeakPtrImpl>>&&, WebCore::NavigationPolicyDecision)>&&, WebCore::PolicyDecisionMode, std::__1::optional<WebCore::NavigationNavigationType>)::$_1, void, WebCore::PolicyAction>::call(WebCore::PolicyAction)
24  0x10bcbb355 WebKit::WebFrame::didReceivePolicyDecision(unsigned long long, WebKit::PolicyDecision&&)
25  0x10b8553b3 decltype(auto) std::__1::apply[abi:sn200100]<WebKit::WebFrameLoaderClient::dispatchDecidePolicyForNavigationAction(WebCore::NavigationAction const&, WebCore::ResourceRequest const&, WebCore::ResourceResponse const&, WebCore::FormState*, WTF::String const&, std::__1::optional<WTF::ObjectIdentifierGeneric<WebCore::NavigationIdentifierType, WTF::ObjectIdentifierMainThreadAccessTraits<unsigned long long>, unsigned long long>>, std::__1::optional<WebCore::HitTestResult>&&, bool, WebCore::NavigationUpgradeToHTTPSBehavior, WTF::OptionSet<WebCore::SandboxFlag, (WTF::ConcurrencyTag)0>, WebCore::PolicyDecisionMode, WTF::CompletionHandler<void (WebCore::PolicyAction)>&&)::$_1, std::__1::tuple<WebKit::PolicyDecision>>(WebKit::WebFrameLoaderClient::dispatchDecidePolicyForNavigationAction(WebCore::NavigationAction const&, WebCore::ResourceRequest const&, WebCore::ResourceResponse const&, WebCore::FormState*, WTF::String const&, std::__1::optional<WTF::ObjectIdentifierGeneric<WebCore::NavigationIdentifierType, WTF::ObjectIdentifierMainThreadAccessTraits<unsigned long long>, unsigned long long>>, std::__1::optional<WebCore::HitTestResult>&&, bool, WebCore::NavigationUpgradeToHTTPSBehavior, WTF::OptionSet<WebCore::SandboxFlag, (WTF::ConcurrencyTag)0>, WebCore::PolicyDecisionMode, WTF::CompletionHandler<void (WebCore::PolicyAction)>&&)::$_1&&, std::__1::tuple<WebKit::PolicyDecision>&&)
26  0x10b855297 WTF::Detail::CallableWrapper<WTF::CompletionHandler<void (IPC::Connection*, IPC::Decoder*)> IPC::Connection::makeAsyncReplyCompletionHandler<Messages::WebPageProxy::DecidePolicyForNavigationActionAsync, WebKit::WebFrameLoaderClient::dispatchDecidePolicyForNavigationAction(WebCore::NavigationAction const&, WebCore::ResourceRequest const&, WebCore::ResourceResponse const&, WebCore::FormState*, WTF::String const&, std::__1::optional<WTF::ObjectIdentifierGeneric<WebCore::NavigationIdentifierType, WTF::ObjectIdentifierMainThreadAccessTraits<unsigned long long>, unsigned long long>>, std::__1::optional<WebCore::HitTestResult>&&, bool, WebCore::NavigationUpgradeToHTTPSBehavior, WTF::OptionSet<WebCore::SandboxFlag, (WTF::ConcurrencyTag)0>, WebCore::PolicyDecisionMode, WTF::CompletionHandler<void (WebCore::PolicyAction)>&&)::$_1>(WebKit::WebFrameLoaderClient::dispatchDecidePolicyForNavigationAction(WebCore::NavigationAction const&, WebCore::ResourceRequest const&, WebCore::ResourceResponse const&, WebCore::FormState*, WTF::String const&, std::__1::optional<WTF::ObjectIdentifierGeneric<WebCore::NavigationIdentifierType, WTF::ObjectIdentifierMainThreadAccessTraits<unsigned long long>, unsigned long long>>, std::__1::optional<WebCore::HitTestResult>&&, bool, WebCore::NavigationUpgradeToHTTPSBehavior, WTF::OptionSet<WebCore::SandboxFlag, (WTF::ConcurrencyTag)0>, WebCore::PolicyDecisionMode, WTF::CompletionHandler<void (WebCore::PolicyAction)>&&)::$_1&&, WTF::ThreadLikeAssertion)::'lambda'(IPC::Connection*, IPC::Decoder*), void, IPC::Connection*, IPC::Decoder*>::call(IPC::Connection*, IPC::Decoder*)
27  0x10b9b6314 IPC::Connection::dispatchMessage(IPC::Decoder&)
28  0x10b9b6472 IPC::Connection::dispatchMessage(WTF::UniqueRef<IPC::Decoder>)
29  0x10b9b65bd IPC::Connection::dispatchOneIncomingMessage()
30  0x10e661ce2 WTF::RunLoop::performWork()
31  0x10e662c42 WTF::RunLoop::performWork(void*)

[Fujii Hironori]

On the other hand, in GTK port,
AsyncScrollingCoordinator::requestScrollToPosition returns early because scrollingNodeID is null.
RenderLayerBacking is not created yet.

[Fujii Hironori]

In Mac port, RenderLayerBacking was created in the following backtrace.

1   0x5ad4e34b2 WebCore::RenderLayer::ensureBacking()
2   0x5ad5041a4 WebCore::RenderLayerCompositor::updateBacking(WebCore::RenderLayer&, WebCore::RenderLayerCompositor::RequiresCompositingData&, WebCore::RenderLayerCompositor::BackingSharingState*, WebCore::RenderLayerCompositor::BackingRequired)
3   0x5ad500a18 WebCore::RenderLayerCompositor::computeCompositingRequirements(WebCore::RenderLayer*, WebCore::RenderLayer&, WebCore::LayerOverlapMap&, WebCore::RenderLayerCompositor::CompositingState&, WebCore::RenderLayerCompositor::BackingSharingState&)
4   0x5ad4feba2 WebCore::RenderLayerCompositor::updateCompositingLayers(WebCore::CompositingUpdateType, WebCore::RenderLayer*)
5   0x5acfb25e1 WebCore::LocalFrameViewLayoutContext::updateCompositingLayersAfterLayoutIfNeeded()
6   0x5aca183d0 WebCore::Document::updateLayout(WTF::OptionSet<WebCore::LayoutOptions, (WTF::ConcurrencyTag)0>, WebCore::Element const*)
7   0x5acfce021 WebCore::Page::setPageScaleFactor(float, WebCore::IntPoint const&, bool)
8   0x5adffaee2 WebCore::HistoryController::restoreScrollPositionAndViewState()
(...)

[Fujii Hironori]

In GTK port, Page::setPageScaleFactor doesn't call Document::updateLayoutIgnorePendingStylesheets because the scroll potion is already restored there.
https://github.com/WebKit/WebKit/blob/a15c64e664f4593adff3723715831074870388d7/Source/WebCore/page/Page.cpp#L1644-L1645

The scroll position was restored by scrollToFocusedElementImmediatelyIfNeeded called by HistoryController::restoreScrollPositionAndViewState.
https://github.com/WebKit/WebKit/blob/a15c64e664f4593adff3723715831074870388d7/Source/WebCore/loader/HistoryController.cpp#L180

[Fujii Hironori]

In Mac port, LocalFrameView::scrollToFocusedElementImmediatelyIfNeeded did nothing because m_shouldScrollToFocusedElement was false.

LocalFrameView::scheduleScrollToFocusedElement wasn't called.

In CachedPage::restore, focusedDocument->focusedElement() returned null.
element->updateFocusAppearance() was not called.

In GTK port, focusedDocument->focusedElement() returned an element.
This patch works around the missing tile problem and all 3 problems in comment#0.

diff --git a/Source/WebCore/history/CachedPage.cpp b/Source/WebCore/history/CachedPage.cpp
index 45e27e1bbdca..884de6a3aa69 100644
--- a/Source/WebCore/history/CachedPage.cpp
+++ b/Source/WebCore/history/CachedPage.cpp
@@ -138,7 +138,7 @@ void CachedPage::restore(Page& page)
         return;
 
     RefPtr focusedDocument = focusedOrMainFrame->document();
-    if (RefPtr element = focusedDocument->focusedElement()) {
+    if (RefPtr element = focusedDocument->focusedElement(); 0) {
 #if PLATFORM(IOS_FAMILY)
         // We don't want focused nodes changing scroll position when restoring from the cache
         // as it can cause ugly jumps before we manage to restore the cached position.

[Fujii Hironori]

In Mac port, the focused element was cleared by clicking "step 2" with the following backtrace.

1   0x1cddf4836 WebCore::Document::setFocusedElement(WebCore::Element*, WebCore::FocusOptions const&, WebCore::BroadcastFocusedElement)
2   0x1cddf5137 WebCore::Document::setFocusedElement(WebCore::Element*, WebCore::BroadcastFocusedElement)
3   0x1ce04b596 WebCore::FocusController::setFocusedElement(WebCore::Element*, WebCore::Frame*, WebCore::FocusOptions const&, WebCore::BroadcastFocusedElement)
4   0x1ce04aa21 WebCore::EventHandler::dispatchMouseEvent(WTF::AtomString const&, WebCore::Node*, int, WebCore::PlatformMouseEvent const&, WebCore::EventHandler::FireMouseOverOut)
5   0x1ccf60d99 WebCore::EventHandler::handleMousePressEvent(WebCore::PlatformMouseEvent const&)
6   0x1bc52b12a WebKit::WebFrame::handleMouseEvent(WebKit::WebMouseEvent const&)
7   0x1bc53b36c WebKit::WebPage::mouseEvent(WTF::ObjectIdentifierGeneric<WebCore::FrameIdentifierType, WTF::ObjectIdentifierMainThreadAccessTraits<unsigned long long>, unsigned long long>, WebKit::WebMouseEvent const&, std::__1::optional<WTF::Vector<WebKit::SandboxExtensionHandle, 0ul, WTF::CrashOnOverflow, 16ul, WTF::FastMalloc>>&&)
8   0x1bc73fdf3 WebKit::WebPage::didReceiveMessage(IPC::Connection&, IPC::Decoder&) (.cold.29)
9   0x1bbdcf6d9 WebKit::WebPage::didReceiveMessage(IPC::Connection&, IPC::Decoder&)
10  0x1bc66d434 IPC::MessageReceiverMap::dispatchMessage(IPC::Connection&, IPC::Decoder&)
11  0x1bc0c7628 WebKit::AuxiliaryProcess::dispatchMessage(IPC::Connection&, IPC::Decoder&)
12  0x1bc6f527a WebKit::AuxiliaryProcess::didReceiveMessage(IPC::Connection&, IPC::Decoder&)
13  0x1bc6692d5 IPC::Connection::dispatchMessage(IPC::Decoder&)
14  0x1bc669472 IPC::Connection::dispatchMessage(WTF::UniqueRef<IPC::Decoder>)
15  0x1bc6695bd IPC::Connection::dispatchOneIncomingMessage()
16  0x1c1df6ce2 WTF::RunLoop::performWork()
17  0x1c1df7c42 WTF::RunLoop::performWork(void*)
18  0x7ff8152f358d __CFRUNLOOP_IS_CALLING_OUT_TO_A_SOURCE0_PERFORM_FUNCTION__
19  0x7ff8152f352f __CFRunLoopDoSource0
20  0x7ff8152f32ea __CFRunLoopDoSources0
21  0x7ff8152f2000 __CFRunLoopRun
22  0x7ff8153a48f0 _CFRunLoopRunSpecificWithOptions
23  0x7ff81700aea7 -[NSRunLoop(NSRunLoop) runMode:beforeDate:]
24  0x7ff816584e9b -[NSRunLoop(NSRunLoop) run]
25  0x7ff814f2d4d1 _xpc_objc_main
26  0x7ff814f3be4a _xpc_main
27  0x7ff814f2d110 _xpc_copy_xpcservice_dictionary
28  0x1bbd7e96c WebKit::XPCServiceMain(int, char const**)
29  0x7ff814e7c781 start

[Fujii Hironori]

HTMLAnchorElement::isMouseFocusable() has #if !(PLATFORM(GTK) || PLATFORM(WPE)).
This causes the problems. 
247257@main added the #if.
https://github.com/WebKit/WebKit/blob/a49c8344113d1f6aa82d9d37738db76245917c1a/Source/WebCore/html/HTMLAnchorElement.cpp#L110-L114

[Fujii Hironori]

This is reproducible with Safari with tabindex. Filed bug#310153.