Implementing document.setRootScroller API for main thread scrolling.

third_party/WebKit/Source/core/dom/Document.cpp

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  *           (C) 2001 Dirk Mueller (mueller@kde.org)
  *           (C) 2006 Alexey Proskuryakov (ap@webkit.org)
  * Copyright (C) 2004, 2005, 2006, 2007, 2008, 2009, 2011, 2012 Apple Inc. All rights reserved.
  * Copyright (C) 2008, 2009 Torch Mobile Inc. All rights reserved. (http://www.torchmobile.com/)
  * Copyright (C) 2008, 2009, 2011, 2012 Google Inc. All rights reserved.
  * Copyright (C) 2010 Nokia Corporation and/or its subsidiary(-ies)
  * Copyright (C) Research In Motion Limited 2010-2011. All rights reserved.
@@ skipping 175 matching lines @@
 #include "core/loader/FrameLoaderClient.h"
 #include "core/loader/ImageLoader.h"
 #include "core/loader/NavigationScheduler.h"
 #include "core/loader/appcache/ApplicationCacheHost.h"
 #include "core/page/ChromeClient.h"
 #include "core/page/EventWithHitTestResults.h"
 #include "core/page/FocusController.h"
 #include "core/page/FrameTree.h"
 #include "core/page/Page.h"
 #include "core/page/PointerLockController.h"
+#include "core/page/scrolling/RootScroller.h"
 #include "core/page/scrolling/ScrollingCoordinator.h"
-#include "core/page/scrolling/ViewportScrollCallback.h"
 #include "core/svg/SVGDocumentExtensions.h"
 #include "core/svg/SVGTitleElement.h"
 #include "core/svg/SVGUseElement.h"
 #include "core/timing/DOMWindowPerformance.h"
 #include "core/timing/Performance.h"
 #include "core/workers/SharedWorkerRepositoryClient.h"
 #include "core/xml/parser/XMLDocumentParser.h"
 #include "platform/DateComponents.h"
 #include "platform/EventDispatchForbiddenScope.h"
 #include "platform/Histogram.h"
@@ skipping 33 matching lines @@
 
 using namespace HTMLNames;
 
 static const unsigned cMaxWriteRecursionDepth = 21;
 
 // This amount of time must have elapsed before we will even consider scheduling a layout without a delay.
 // FIXME: For faster machines this value can really be lowered to 200.  250 is adequate, but a little high
 // for dual G5s. :)
 static const int cLayoutScheduleThreshold = 250;
 
-namespace {
-
-void updateViewportApplyScroll(Element* documentElement)
-{
-    if (!documentElement
-        || !documentElement->isHTMLElement()
-        || documentElement->document().ownerElement())
-        return;
-
-    if (documentElement->getApplyScroll())
-        return;
-
-    ScrollStateCallback* applyScroll =
-        new ViewportScrollCallback(documentElement->document());
-
-    // Use disable-native-scroll since the ViewportScrollCallback needs to
-    // apply scroll actions before (TopControls) and after (overscroll)
-    // scrolling the element so it applies scroll to the element itself.
-    documentElement->setApplyScroll(
-        applyScroll,
-        "disable-native-scroll");
-}
-
-} // namespace
-
 // DOM Level 2 says (letters added):
 //
 // a) Name start characters must have one of the categories Ll, Lu, Lo, Lt, Nl.
 // b) Name characters other than Name-start characters must have one of the categories Mc, Me, Mn, Lm, or Nd.
 // c) Characters in the compatibility area (i.e. with character code greater than #xF900 and less than #xFFFE) are not allowed in XML names.
 // d) Characters which have a font or compatibility decomposition (i.e. those with a "compatibility formatting tag" in field 5 of the database -- marked by field 5 beginning with a "<") are not allowed.
 // e) The following characters are treated as name-start characters rather than name characters, because the property file classifies them as Alphabetic: [#x02BB-#x02C1], #x0559, #x06E5, #x06E6.
 // f) Characters #x20DD-#x20E0 are excluded (in accordance with Unicode, section 5.14).
 // g) Character #x00B7 is classified as an extender, because the property list so identifies it.
 // h) Character #x0387 is added as a name character, because #x00B7 is its canonical equivalent.
@@ skipping 316 matching lines @@
     if (!frame())
         return 0;
 
     return domWindow()->location();
 }
 
 void Document::childrenChanged(const ChildrenChange& change)
 {
     ContainerNode::childrenChanged(change);
     m_documentElement = ElementTraversal::firstWithin(*this);
+}
 
-    // Installs the viewport scrolling callback (the "applyScroll" in Scroll
-    // Customization lingo) on the documentElement. This callback is
-    // responsible for viewport related scroll actions like top controls
-    // movement and overscroll glow as well as actually scrolling the root
-    // viewport.
-    updateViewportApplyScroll(m_documentElement);
+void Document::setRootScroller(Element* newScroller, ExceptionState& exceptionState)
+{
+    DCHECK(newScroller);
+
+    if (ownerElement()) {
+        exceptionState.throwDOMException(
+            WrongDocumentError,
+            "Root scroller can only be set on the top-level document.");

[tdresser, 2016/04/26 20:43:49]

These are web developer facing - would we devs know what we mean by top-level
document?

Maybe:

"Elements within frames cannot become the root scroller."

[bokan, 2016/04/26 23:06:23]

Done.

+        return;
+    }
+
+    if (newScroller->document() != this) {
+        exceptionState.throwDOMException(
+            WrongDocumentError,
+            "Element isn't part of this document.");
+        return;
+    }
+
+    FrameHost* host = frameHost();
+    if (!host)
+        return;
+
+    RootScroller* rootScroller = host->rootScroller();
+    DCHECK(rootScroller);
+
+    if (!rootScroller->set(*newScroller)) {
+        exceptionState.throwDOMException(
+            InvalidStateError,
+            "Element cannot be set as root scroller.");

[tdresser, 2016/04/26 20:43:50]

In what cases could this happen? Can we be more specific? Does it need to be
display:block, or something like that?

[bokan, 2016/04/26 23:06:23]

I'm being intentionally vague here, it's one of the pieces in the proposal that
hasn't been decided yet and I expect it to change. That said, my initial
implementation checks for block and iframe so I'll put that in the string.

+    }
+}
+
+Element* Document::rootScroller()
+{
+    if (ownerElement())
+        return documentElement();
+
+    FrameHost* host = frameHost();
+    if (!host)
+        return nullptr;
+
+    RootScroller* rootScroller = host->rootScroller();
+    DCHECK(rootScroller);
+
+    updateLayoutIgnorePendingStylesheets();
+
+    return rootScroller->getCurrent();
 }
 
 AtomicString Document::convertLocalName(const AtomicString& name)
 {
     return isHTMLDocument() ? name.lower() : name;
 }
 
 Element* Document::createElement(const AtomicString& name, ExceptionState& exceptionState)
 {
     if (!isValidName(name)) {
@@ skipping 1278 matching lines @@
     // suppressed for them. We're interested in tracking the time of the
     // first real or 'paintable' layout.
     // TODO(esprehn): This doesn't really make sense, why not track the first
     // beginFrame? This will catch the first layout in a page that does lots
     // of layout thrashing even though that layout might not be followed by
     // a paint for many seconds.
     if (isRenderingReady() && body() && !styleEngine().hasPendingSheets()) {
         if (!m_documentTiming.firstLayout())
             m_documentTiming.markFirstLayout();
     }
+
+    if (!ownerElement() && frameHost()) {
+        if (RootScroller* rootScroller = frameHost()->rootScroller())
+            rootScroller->didUpdateTopDocumentLayout();
+    }
 }
 
 void Document::setNeedsFocusedElementCheck()
 {
     setNeedsStyleRecalc(LocalStyleChange, StyleChangeReasonForTracing::createWithExtraData(StyleChangeReason::PseudoClass, StyleChangeExtraData::Focus));
 }
 
 void Document::clearFocusedElementSoon()
 {
     if (!m_clearFocusedElementTimer.isActive())
@@ skipping 3978 matching lines @@
 #ifndef NDEBUG
 using namespace blink;
 void showLiveDocumentInstances()
 {
     Document::WeakDocumentSet& set = Document::liveDocumentSet();
     fprintf(stderr, "There are %u documents currently alive:\n", set.size());
     for (Document* document : set)
         fprintf(stderr, "- Document %p URL: %s\n", document, document->url().getString().utf8().data());
 }
 #endif