Adapt to forced scroll-wheel latching

Handle that Chromium now requires all wheel events to be phases despite
them not being phased on the majority of platforms.

Change-Id: Iabd5630652c0d8fd67563db3d63ef1f2f528c35c
Reviewed-by: Michael Brüning <michael.bruning@qt.io>

4 files changed, 28 insertions, 13 deletions

diff --git a/src/core/render_widget_host_view_qt.cpp b/src/core/render_widget_host_view_qt.cpp
index 15881674c..737f42439 100644
--- a/src/core/render_widget_host_view_qt.cpp
+++ b/src/core/render_widget_host_view_qt.cpp
@@ -332,6 +332,7 @@ RenderWidgetHostViewQt::RenderWidgetHostViewQt(content::RenderWidgetHost *widget
     , m_cursorPosition(0)
     , m_emptyPreviousSelection(true)
     , m_wheelAckPending(false)
+    , m_mouseWheelPhaseHandler(this)
 {
     host()->SetView(this);
 #ifndef QT_NO_ACCESSIBILITY
@@ -1421,8 +1422,10 @@ void RenderWidgetHostViewQt::handleWheelEvent(QWheelEvent *ev)
 {
     if (!m_wheelAckPending) {
         Q_ASSERT(m_pendingWheelEvents.isEmpty());
-        m_wheelAckPending = true;
-        host()->ForwardWheelEvent(WebEventFactory::toWebWheelEvent(ev, dpiScale()));
+        blink::WebMouseWheelEvent webEvent = WebEventFactory::toWebWheelEvent(ev, dpiScale());
+        m_wheelAckPending = (webEvent.phase != blink::WebMouseWheelEvent::kPhaseEnded);
+        m_mouseWheelPhaseHandler.AddPhaseIfNeededAndScheduleEndEvent(webEvent, false);
+        host()->ForwardWheelEvent(webEvent);
         return;
     }
     if (!m_pendingWheelEvents.isEmpty()) {
@@ -1433,16 +1436,26 @@ void RenderWidgetHostViewQt::handleWheelEvent(QWheelEvent *ev)
     m_pendingWheelEvents.append(WebEventFactory::toWebWheelEvent(ev, dpiScale()));
 }
 
-void RenderWidgetHostViewQt::WheelEventAck(const blink::WebMouseWheelEvent &/*event*/, content::InputEventAckState /*ack_result*/)
+void RenderWidgetHostViewQt::WheelEventAck(const blink::WebMouseWheelEvent &event, content::InputEventAckState /*ack_result*/)
 {
+    if (event.phase == blink::WebMouseWheelEvent::kPhaseEnded)
+        return;
+    Q_ASSERT(m_wheelAckPending);
     m_wheelAckPending = false;
-    if (!m_pendingWheelEvents.isEmpty()) {
-        m_wheelAckPending = true;
-        host()->ForwardWheelEvent(m_pendingWheelEvents.takeFirst());
+    while (!m_pendingWheelEvents.isEmpty() && !m_wheelAckPending) {
+        blink::WebMouseWheelEvent webEvent = m_pendingWheelEvents.takeFirst();
+        m_wheelAckPending = (webEvent.phase != blink::WebMouseWheelEvent::kPhaseEnded);
+        m_mouseWheelPhaseHandler.AddPhaseIfNeededAndScheduleEndEvent(webEvent, false);
+        host()->ForwardWheelEvent(webEvent);
     }
     // TODO: We could forward unhandled wheelevents to our parent.
 }
 
+content::MouseWheelPhaseHandler *RenderWidgetHostViewQt::GetMouseWheelPhaseHandler()
+{
+    return &m_mouseWheelPhaseHandler;
+}
+
 void RenderWidgetHostViewQt::clearPreviousTouchMotionState()
 {
     m_previousTouchPoints.clear();
diff --git a/src/core/render_widget_host_view_qt.h b/src/core/render_widget_host_view_qt.h
index 26fd16631..92cc422a8 100644
--- a/src/core/render_widget_host_view_qt.h
+++ b/src/core/render_widget_host_view_qt.h
@@ -46,6 +46,7 @@
 #include "components/viz/common/frame_sinks/begin_frame_source.h"
 #include "components/viz/common/resources/transferable_resource.h"
 #include "content/browser/accessibility/browser_accessibility_manager.h"
+#include "content/browser/renderer_host/input/mouse_wheel_phase_handler.h"
 #include "content/browser/renderer_host/render_widget_host_view_base.h"
 #include "content/browser/renderer_host/text_input_manager.h"
 #include "content/common/view_messages.h"
@@ -141,6 +142,7 @@ public:
     void DidCreateNewRendererCompositorFrameSink(viz::mojom::CompositorFrameSinkClient* renderer_compositor_frame_sink) override;
     void SubmitCompositorFrame(const viz::LocalSurfaceId&, viz::CompositorFrame, base::Optional<viz::HitTestRegionList>) override;
     void WheelEventAck(const blink::WebMouseWheelEvent &event, content::InputEventAckState ack_result) override;
+    content::MouseWheelPhaseHandler *GetMouseWheelPhaseHandler() override;
 
     void GetScreenInfo(content::ScreenInfo* results) const override;
     gfx::Rect GetBoundsInRootWindow() override;
@@ -255,6 +257,7 @@ private:
 
     bool m_wheelAckPending;
     QList<blink::WebMouseWheelEvent> m_pendingWheelEvents;
+    content::MouseWheelPhaseHandler m_mouseWheelPhaseHandler;
 
     std::string m_editCommand;
 };
diff --git a/src/core/web_engine_context.cpp b/src/core/web_engine_context.cpp
index 4b0a2f6cd..e2c127b22 100644
--- a/src/core/web_engine_context.cpp
+++ b/src/core/web_engine_context.cpp
@@ -417,8 +417,6 @@ WebEngineContext::WebEngineContext()
     appendToFeatureSwitch(parsedCommandLine, switches::kEnableFeatures, features::kAllowContentInitiatedDataUrlNavigations.name);
     // Surface synchronization breaks our current graphics integration (since 65)
     appendToFeatureSwitch(parsedCommandLine, switches::kDisableFeatures, features::kEnableSurfaceSynchronization.name);
-    // Scroll latching expects phases on all wheel events when it really only makes sense for simulated ones.
-    appendToFeatureSwitch(parsedCommandLine, switches::kDisableFeatures, features::kTouchpadAndWheelScrollLatching.name);
 
     if (useEmbeddedSwitches) {
         appendToFeatureSwitch(parsedCommandLine, switches::kEnableFeatures, features::kOverlayScrollbar.name);
diff --git a/src/core/web_event_factory.cpp b/src/core/web_event_factory.cpp
index b97235ceb..479fc38f8 100644
--- a/src/core/web_event_factory.cpp
+++ b/src/core/web_event_factory.cpp
@@ -1422,13 +1422,14 @@ static void setBlinkWheelEventDelta(blink::WebMouseWheelEvent &webEvent)
     webEvent.delta_y = webEvent.wheel_ticks_y * wheelScrollLines * cDefaultQtScrollStep;
 }
 
-blink::WebMouseWheelEvent::Phase toBlinkPhase(Qt::ScrollPhase phase)
+blink::WebMouseWheelEvent::Phase toBlinkPhase(QWheelEvent *ev)
 {
-    switch (phase) {
+    switch (ev->phase()) {
     case Qt::NoScrollPhase:
+    case Qt::ScrollMomentum:
         return blink::WebMouseWheelEvent::kPhaseNone;
     case Qt::ScrollBegin:
-        return blink::WebMouseWheelEvent::kPhaseBegan;
+        return ev->angleDelta().isNull() ? blink::WebMouseWheelEvent::kPhaseMayBegin : blink::WebMouseWheelEvent::kPhaseBegan;
     case Qt::ScrollUpdate:
         return blink::WebMouseWheelEvent::kPhaseChanged;
     case Qt::ScrollEnd:
@@ -1449,7 +1450,7 @@ blink::WebMouseWheelEvent WebEventFactory::toWebWheelEvent(QWheelEvent *ev, doub
 
     webEvent.wheel_ticks_x = static_cast<float>(ev->angleDelta().x()) / QWheelEvent::DefaultDeltasPerStep;
     webEvent.wheel_ticks_y = static_cast<float>(ev->angleDelta().y()) / QWheelEvent::DefaultDeltasPerStep;
-    webEvent.phase = toBlinkPhase(ev->phase());
+    webEvent.phase = toBlinkPhase(ev);
     webEvent.has_precise_scrolling_deltas = true;
     setBlinkWheelEventDelta(webEvent);
 
@@ -1462,7 +1463,7 @@ bool WebEventFactory::coalesceWebWheelEvent(blink::WebMouseWheelEvent &webEvent,
         return false;
     if (modifiersForEvent(ev) != webEvent.GetModifiers())
         return false;
-    if (toBlinkPhase(ev->phase()) != webEvent.phase)
+    if (toBlinkPhase(ev) != webEvent.phase)
         return false;
 
     webEvent.SetTimeStamp(currentTimeForEvent(ev));