Implement top controls show/hide functionality for main thread scrolling

Source/core/frame/TopControls.cpp

Index: Source/core/frame/TopControls.cpp
diff --git a/Source/core/frame/TopControls.cpp b/Source/core/frame/TopControls.cpp
new file mode 100644
index 0000000000000000000000000000000000000000..3a0d9243fa8f42d087e64a6bc2f9c94d4fe39f4e
--- /dev/null
+++ b/Source/core/frame/TopControls.cpp
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+/*
+ * 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 "core/frame/FrameHost.h"
+#include "core/page/Chrome.h"
+#include "core/page/ChromeClient.h"
+#include "platform/geometry/FloatSize.h"
+#include <algorithm> // for std::min and std::max
+
+namespace blink {
+
+TopControls::TopControls(const FrameHost& frameHost)
+    : m_frameHost(frameHost)
+    , m_height(0)
+    , m_shownRatio(0)
+    , m_baselineContentOffset(0)
+    , m_accumulatedScrollDelta(0)
+    , m_shrinkViewport(false)
+    , m_permittedState(WebTopControlsBoth)
+{
+}
+
+void TopControls::scrollBegin()
+{
+    resetBaseline();
+}
+
+FloatSize TopControls::scrollBy(FloatSize pendingDelta)
+{
+    if ((m_permittedState == WebTopControlsShown && pendingDelta.height() < 0) || (m_permittedState == WebTopControlsHidden && pendingDelta.height() > 0))
+        return pendingDelta;
+
+    if (m_height == 0)
+        return pendingDelta;
+
+    float oldOffset = contentOffset();
+
+    // Update accumulated vertical scroll and apply it to top controls
+    m_accumulatedScrollDelta += pendingDelta.height();
+    setShownRatio((m_baselineContentOffset + m_accumulatedScrollDelta) / m_height);
+
+    // Reset baseline when controls are fully visible
+    if (m_shownRatio == 1)
+        resetBaseline();
+
+    FloatSize appliedDelta(0, contentOffset() - oldOffset);
+    return pendingDelta - appliedDelta;
+}
+
+void TopControls::resetBaseline()
+{
+    m_accumulatedScrollDelta = 0;
+    m_baselineContentOffset = contentOffset();
+}
+
+float TopControls::layoutHeight()
+{
+    return m_shrinkViewport ? m_height : 0;
+}
+
+float TopControls::contentOffset()
+{
+    return m_shownRatio * m_height;
+}
+
+void TopControls::setShownRatio(float shownRatio)
+{
+    shownRatio = std::min(shownRatio, 1.f);
+    shownRatio = std::max(shownRatio, 0.f);
+
+    if (m_shownRatio == shownRatio)
+        return;
+
+    m_shownRatio = shownRatio;
+    m_frameHost.chrome().client().didUpdateTopControls();
+}
+
+void TopControls::updateConstraints(WebTopControlsState constraints)
+{
+    m_permittedState = constraints;
+}
+
+void TopControls::setHeight(float height, bool shrinkViewport)
+{
+    if (m_height == height && m_shrinkViewport == shrinkViewport)
+        return;
+
+    m_height = height;
+    m_shrinkViewport = shrinkViewport;
+    m_frameHost.chrome().client().didUpdateTopControls();
+}
+
+} // namespace blink