Improve mobile device rotation behavior.

Source/WebKit/chromium/src/ViewportAnchor.cpp

Index: Source/WebKit/chromium/src/ViewportAnchor.cpp
diff --git a/Source/WebKit/chromium/src/ViewportAnchor.cpp b/Source/WebKit/chromium/src/ViewportAnchor.cpp
new file mode 100644
index 0000000000000000000000000000000000000000..8e597b5589aa20d3a1474927ca07f4c7022ad159
--- /dev/null
+++ b/Source/WebKit/chromium/src/ViewportAnchor.cpp
@@ -0,0 +1,131 @@
+/*
+ * Copyright (C) 2013 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:
+ *
+ *     * Redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer.
+ *     * 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.
+ *     * Neither the name of Google Inc. nor the names of its
+ * contributors may be used to endorse or promote products derived from
+ * this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND 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 THE COPYRIGHT
+ * OWNER OR 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 "ViewportAnchor.h"
+
+#include "ContainerNode.h"
+#include "EventHandler.h"
+#include "HitTestResult.h"
+#include "Node.h"
+
+#if ENABLE(VIEWPORT)
+
+using namespace WebCore;
+
+namespace WebKit {
+
+namespace {
+
+static const float viewportAnchorRelativeEpsilon = 0.1f;
+static const int viewportToNodeMaxRelativeArea = 2;
+
+template <typename RectType>
+int area(const RectType& rect) {
+    return rect.width() * rect.height();
+}
+
+Node* findNonEmptyAnchorNode(const IntPoint& point, const IntRect& viewRect, EventHandler* eventHandler)
+{
+    Node* node = eventHandler->hitTestResultAtPoint(point).innerNode();
+
+    // If the node bounding box is sufficiently large, make a single attempt to
+    // find a smaller node; the larger the node bounds, the greater the
+    // variability under resize.
+    const int maxNodeArea = area(viewRect) * viewportToNodeMaxRelativeArea;
+    if (node && area(node->boundingBox()) > maxNodeArea) {
+        IntSize pointOffset = viewRect.size();
+        pointOffset.scale(viewportAnchorRelativeEpsilon);
+        node = eventHandler->hitTestResultAtPoint(point + pointOffset).innerNode();
+    }
+
+    while (node && node->boundingBox().isEmpty())
+        node = node->parentNode();
+
+    return node;
+}
+
+} // namespace
+
+ViewportAnchor::ViewportAnchor(EventHandler* eventHandler)
+    : m_eventHandler(eventHandler) { }
+
+void ViewportAnchor::setAnchor(const IntRect& viewRect, const FloatSize& anchorInViewCoords)
+{
+    m_viewRect = viewRect;
+    m_anchorNode.clear();
+    m_anchorNodeBounds = LayoutRect();
+    m_anchorInNodeCoords = FloatSize();
+    m_anchorInViewCoords = anchorInViewCoords;
+
+    if (viewRect.isEmpty())
+        return;
+
+    // Preserve origins at the absolute screen origin
+    if (viewRect.location() == IntPoint::zero())
+        return;
+
+    FloatSize anchorOffset = viewRect.size();
+    anchorOffset.scale(anchorInViewCoords.width(), anchorInViewCoords.height());
+    const FloatPoint anchorPoint = FloatPoint(viewRect.location()) + anchorOffset;
+
+    Node* node = findNonEmptyAnchorNode(flooredIntPoint(anchorPoint), viewRect, m_eventHandler);
+    if (!node)
+        return;
+
+    m_anchorNode = node;
+    m_anchorNodeBounds = node->boundingBox();
+    m_anchorInNodeCoords = anchorPoint - m_anchorNodeBounds.location();
+    m_anchorInNodeCoords.scale(1.f / m_anchorNodeBounds.width(), 1.f / m_anchorNodeBounds.height());
+}
+
+IntPoint ViewportAnchor::computeOrigin(const IntSize& currentViewSize) const
+{
+    if (!m_anchorNode || !m_anchorNode->inDocument())
+        return m_viewRect.location();
+
+    const LayoutRect currentNodeBounds = m_anchorNode->boundingBox();
+    if (m_anchorNodeBounds == currentNodeBounds)
+        return m_viewRect.location();
+
+    // Compute the new anchor point relative to the node position
+    FloatSize anchorOffsetFromNode = currentNodeBounds.size();
+    anchorOffsetFromNode.scale(m_anchorInNodeCoords.width(), m_anchorInNodeCoords.height());
+    FloatPoint anchorPoint = currentNodeBounds.location() + anchorOffsetFromNode;
+
+    // Compute the new origin point relative to the new anchor point
+    FloatSize anchorOffsetFromOrigin = currentViewSize;
+    anchorOffsetFromOrigin.scale(m_anchorInViewCoords.width(), m_anchorInViewCoords.height());
+    return flooredIntPoint(anchorPoint - anchorOffsetFromOrigin);
+}
+
+} // namespace WebKit
+
+#endif // ENABLE(VIEWPORT)