Implement top controls show/hide functionality for main thread scrolling

Source/web/TopControls.cpp

+/*
+ * Copyright (C) 2015 Google Inc. All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ *
+ * 1.  Redistributions of source code must retain the above copyright
+ *     notice, this list of conditions and the following disclaimer.
+ * 2.  Redistributions in binary form must reproduce the above copyright
+ *     notice, this list of conditions and the following disclaimer in the
+ *     documentation and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY APPLE AND ITS CONTRIBUTORS "AS IS" AND ANY
+ * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
+ * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL APPLE OR ITS CONTRIBUTORS BE LIABLE FOR ANY
+ * DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
+ * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
+ * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
+ * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
+ * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include "config.h"
+#include "TopControls.h"
+
+#include "platform/PlatformGestureEvent.h"
+#include "web/WebViewImpl.h"
+#include <algorithm> // for std::min and std::max
+
+namespace blink {
+
+TopControls::TopControls(WebViewImpl* webView)
+    : m_webView(webView)
+    , m_height(0)
+    , m_shownRatio(0)
+    , m_baselineContentOffset(0)
+    , m_accumulatedScrollDelta(0)
+    , m_shrinkViewport(false)
+    , m_permittedState(WebTopControlsBoth)
+    , m_pinchGestureActive(false)
+{
+}
+
+bool TopControls::handleGestureEvent(const PlatformGestureEvent& event, float* remainingDeltaY)
+{
+    switch (event.type()) {
+    case PlatformEvent::GestureScrollBegin:
+        scrollBegin();
+        break;
+    case PlatformEvent::GestureScrollUpdate:
+        if (m_webView->shouldTopControlsConsumeScroll(event.deltaY())) {
+            *remainingDeltaY = scrollBy(event.deltaY());
+        } else {
+            *remainingDeltaY = event.deltaY();
+        }
+        return *remainingDeltaY != event.deltaY();
+    case PlatformEvent::GesturePinchBegin:
+        m_pinchGestureActive = true;
+        break;
+    case PlatformEvent::GesturePinchEnd:
+        m_pinchGestureActive = false;
+        break;
+    default:
+        break;
+    }
+
+    return false;
+}
+
+void TopControls::scrollBegin()
+{
+    resetBaseline();
+}
+
+float TopControls::scrollBy(float pendingDelta)
+{
+    if (m_pinchGestureActive)
+        return pendingDelta;
+
+    if ((m_permittedState == WebTopControlsShown && pendingDelta < 0) || (m_permittedState == WebTopControlsHidden && pendingDelta > 0))
+        return pendingDelta;
+
+    if (m_height == 0.f)
+        return pendingDelta;
+
+    float oldOffset = contentOffset();
+
+    // Update accumulated vertical scroll and apply it to top controls
+    m_accumulatedScrollDelta += pendingDelta;
+    setShownRatio((m_baselineContentOffset + m_accumulatedScrollDelta) / m_height);
+
+    // Reset baseline when controls are fully visible
+    if (m_shownRatio == 1.f)
+        resetBaseline();
+
+    float appliedDelta = contentOffset() - oldOffset;
+    return pendingDelta - appliedDelta;
+}
+
+void TopControls::resetBaseline()
+{
+    m_accumulatedScrollDelta = 0.f;
+    m_baselineContentOffset = contentOffset();
+}
+
+float TopControls::layoutHeight()
+{
+    return m_shrinkViewport ? m_height : 0.f;
+}
+
+float TopControls::contentOffset()
+{
+    return m_shownRatio * m_height;
+}
+
+void TopControls::setShownRatio(float offset)
+{
+    // Clamp
+    offset = std::min(offset, 1.f);
+    offset = std::max(offset, 0.f);
+
+    if (m_shownRatio == offset)
+        return;
+
+    m_shownRatio = offset;
+    m_webView->didUpdateTopControls();
+}
+
+void TopControls::updateShownRatio(float delta)
+{
+    setShownRatio(m_shownRatio + delta);
+}
+
+void TopControls::updateState(
+    WebTopControlsState constraints,
+    WebTopControlsState current,
+    bool animate)
+{
+    // CC handles current state and animate so they are ignored here.
+    m_permittedState = constraints;
+}
+
+void TopControls::setHeight(float height)
+{
+    if (m_height == height)
+        return;
+
+    m_height = height;
+    m_webView->didUpdateTopControls();
+}
+
+void TopControls::setShrinkViewport(bool shrinkViewport)
+{
+    if (m_shrinkViewport == shrinkViewport)
+        return;
+
+    m_shrinkViewport = shrinkViewport;
+    m_webView->didUpdateTopControls();
+}
+} // namespace blink