Blink Support for Overlay Scrollbar Animation

Source/platform/scroll/ScrollbarStateTransitionAnimator.cpp

Index: Source/platform/scroll/ScrollbarStateTransitionAnimator.cpp
diff --git a/Source/platform/scroll/ScrollbarStateTransitionAnimator.cpp b/Source/platform/scroll/ScrollbarStateTransitionAnimator.cpp
new file mode 100644
index 0000000000000000000000000000000000000000..ae12f8713c6c1e91ea6f227f3c6b5a913f32ebfa
--- /dev/null
+++ b/Source/platform/scroll/ScrollbarStateTransitionAnimator.cpp
@@ -0,0 +1,204 @@
+// 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 "platform/scroll/ScrollbarStateTransitionAnimator.h"
+
+#include "platform/TraceEvent.h"
+#include "platform/scroll/ScrollableArea.h"
+#include "wtf/CurrentTime.h"
+#include "wtf/PassOwnPtr.h"
+#include <algorithm>
+
+using namespace std;
+
+namespace {
+// This number is calculated from scrollbar animation controller thinning. It is supposed to last 300 milliseconds.
+const double kDefaultStateTransitionTime = 0.3;
+
+} // namespace
+
+namespace blink {
+
+PassOwnPtr<ScrollbarStateTransitionAnimator> ScrollbarStateTransitionAnimator::create(ScrollableArea* scrollableArea)
+{
+    if (scrollableArea->hasOverlayScrollbars())
+        return adoptPtr(new ScrollbarStateTransitionAnimator(scrollableArea));
+    return PassOwnPtr<ScrollbarStateTransitionAnimator>();
+}
+
+ScrollbarStateTransitionAnimator::StateTransitionData::StateTransitionData(ScrollbarStateTransitionAnimator* parent)
+{
+    reset();
+}
+
+void ScrollbarStateTransitionAnimator::StateTransitionData::reset()
+{
+    m_startTime = 0;
+    m_animationTime = kDefaultStateTransitionTime;
+    m_lastAnimatedTime = 0;
+    m_progress = 0;
+    m_startState = blink::WebThemeEngine::StateDisabled;
+    m_endState = blink::WebThemeEngine::StateDisabled;
+}
+
+void ScrollbarStateTransitionAnimator::StateTransitionData::startStateTransitionAnimation(double currentTime, blink::WebThemeEngine::State startState, blink::WebThemeEngine::State endState, const Parameters parameters)
+{
+    if (m_startTime) {
+        // Animation is going on. This is probably because we need to reverse animation state.
+        if (startState == m_endState || endState == m_startState) {
+            // Since one set of the state could be either hover/pressed, check whether the other
+            // state is the same. (normal state)
+            double progressedTime = currentTime - m_startTime;
+            // startTime is used to calculate progress, we are faking a startTime.
+            m_startTime = currentTime - (m_animationTime - progressedTime);
+            m_progress = 1 - m_progress;
+        }
+    } else {
+        m_startTime = currentTime;
+        m_progress = 0;
+    }
+    m_startState = startState;
+    m_endState = endState;
+}
+
+bool ScrollbarStateTransitionAnimator::StateTransitionData::animate(double currentTime)
+{
+    if (!duringAnimation(currentTime)) {
+        // Animation should end.
+        reset();
+        m_lastAnimatedTime = currentTime;
+        return false;
+    }
+
+    m_progress = (currentTime - m_startTime) / m_animationTime;
+
+    // Store progress of size/opacity so ScrollbarTheme can read.
+    return true;
+}
+
+bool ScrollbarStateTransitionAnimator::StateTransitionData::duringAnimation(double currentTime) const
+{
+    return m_startTime && m_startTime <= currentTime && currentTime <= m_startTime + m_animationTime;
+}
+
+ScrollbarStateTransitionAnimator::ScrollbarStateTransitionAnimator(ScrollableArea* scrollableArea)
+    : m_scrollableArea(scrollableArea)
+    , m_data(this)
+    , m_animationActive(false)
+{
+    m_parameters.m_isEnabled = scrollableArea->hasOverlayScrollbars();
+    m_parameters.m_animationTime = kDefaultStateTransitionTime;
+}
+
+ScrollbarStateTransitionAnimator::~ScrollbarStateTransitionAnimator()
+{
+    stopAnimationTimerIfNeeded();
+}
+
+void ScrollbarStateTransitionAnimator::cancelAnimations()
+{
+    m_animationActive = false;
+}
+
+void ScrollbarStateTransitionAnimator::serviceAnimations()
+{
+    if (m_animationActive)
+        animationTimerFired();
+}
+
+void ScrollbarStateTransitionAnimator::mouseEnteredScrollbar(Scrollbar* scrollbar)
+{
+    if (!m_parameters.m_isEnabled)
+        return;
+
+    // Start transition from normal to hover/pressed.
+    double currentTime = this->currentTime();
+    blink::WebThemeEngine::State startState = blink::WebThemeEngine::StateNormal;
+    blink::WebThemeEngine::State endState = blink::WebThemeEngine::StateHover;
+
+    if (scrollbar) {
+        ScrollbarPart pressedPart = scrollbar->pressedPart();
+        if (pressedPart == ThumbPart)
+            endState = blink::WebThemeEngine::StatePressed;
+    }
+
+    m_data.startStateTransitionAnimation(currentTime, startState, endState, m_parameters);
+    animationWillStart();
+    animationTimerFired();
+}
+
+void ScrollbarStateTransitionAnimator::mouseExitedScrollbar(Scrollbar* scrollbar)
+{
+    if (!m_parameters.m_isEnabled)
+        return;
+
+    // Start transition from hover/pressed to normal.
+    double currentTime = this->currentTime();
+    blink::WebThemeEngine::State endState = blink::WebThemeEngine::StateNormal;
+    blink::WebThemeEngine::State startState = blink::WebThemeEngine::StateHover;
+
+    if (scrollbar) {
+        ScrollbarPart pressedPart = scrollbar->pressedPart();
+        if (pressedPart == ThumbPart)
+            endState = blink::WebThemeEngine::StatePressed;
+    }
+
+    m_data.startStateTransitionAnimation(currentTime, startState, endState, m_parameters);
+    animationWillStart();
+    animationTimerFired();
+}
+
+bool ScrollbarStateTransitionAnimator::isDuringStateTransitionAnimation() const
+{
+    double currentTime = this->currentTime();
+    return m_animationActive && m_data.duringAnimation(currentTime);
+}
+
+void ScrollbarStateTransitionAnimator::notifyStateTransitionInProgress() const
+{
+    m_scrollableArea->stateTransitionInProgress();
+}
+
+void ScrollbarStateTransitionAnimator::animationTimerFired()
+{
+    TRACE_EVENT0("webkit", "ScrollbarStateTransitionAnimator::animationTimerFired");
+
+    double currentTime = this->currentTime();
+
+    if (m_data.animate(currentTime)) {
+        startNextTimer();
+    } else {
+        m_animationActive = false;
+        animationDidFinish();
+    }
+
+    notifyStateTransitionInProgress();
+}
+
+void ScrollbarStateTransitionAnimator::startNextTimer()
+{
+    if (scrollableArea()->scheduleAnimation())
+        m_animationActive = true;
+}
+
+bool ScrollbarStateTransitionAnimator::animationTimerActive()
+{
+    return m_animationActive;
+}
+
+void ScrollbarStateTransitionAnimator::stopAnimationTimerIfNeeded()
+{
+    if (animationTimerActive()) {
+        m_animationActive = false;
+    }
+}
+
+double ScrollbarStateTransitionAnimator::currentTime() const
+{
+    return WTF::monotonicallyIncreasingTime();
+}
+
+} // namespace WebCore