Implement pinch-zoom scaling for main-frame scrollbars and pinch-zoom overlay scrollbars.

cc/layer_impl.cc

Index: cc/layer_impl.cc
diff --git a/cc/layer_impl.cc b/cc/layer_impl.cc
index 8545e42f7336acf9fffbedd72ca9d3549dd1cfe0..ea1ddae2fa924f5f425a79c5bd80d92bf9ad896c 100644
--- a/cc/layer_impl.cc
+++ b/cc/layer_impl.cc
@@ -56,6 +56,8 @@ LayerImpl::LayerImpl(LayerTreeImpl* treeImpl, int id)
 #endif
     , m_horizontalScrollbarLayer(0)
     , m_verticalScrollbarLayer(0)
+    , m_horizontalPinchZoomScrollbarLayer(0)
+    , m_verticalPinchZoomScrollbarLayer(0)
 {
     DCHECK(m_layerId > 0);
     DCHECK(m_layerTreeImpl);
@@ -836,6 +838,16 @@ void LayerImpl::updateScrollbarPositions()
         m_verticalScrollbarLayer->setTotalSize(m_bounds.height());
         m_verticalScrollbarLayer->setMaximum(m_maxScrollOffset.y());
     }
+    if (m_horizontalPinchZoomScrollbarLayer) {
+        m_horizontalPinchZoomScrollbarLayer->setCurrentPos(currentOffset.x());
+        m_horizontalPinchZoomScrollbarLayer->setTotalSize(m_bounds.width());
+        m_horizontalPinchZoomScrollbarLayer->setMaximum(m_maxScrollOffset.x());
+    }
+    if (m_verticalPinchZoomScrollbarLayer) {
+        m_verticalPinchZoomScrollbarLayer->setCurrentPos(currentOffset.y());
+        m_verticalPinchZoomScrollbarLayer->setTotalSize(m_bounds.height());
+        m_verticalPinchZoomScrollbarLayer->setMaximum(m_maxScrollOffset.y());
+    }
 
     if (currentOffset == m_lastScrollOffset)
         return;
@@ -889,11 +901,48 @@ void LayerImpl::setScrollDelta(const gfx::Vector2dF& scrollDelta)
 
 void LayerImpl::setImplTransform(const gfx::Transform& transform)
 {
-    if (m_implTransform == transform)
+    // TODO(wjmaclean) - do not commit the changes in this function
+    // yet! I've included them in this patch to show the eventual
+    // mechanism I propose for mainframe scrollbar scaling,
+    // but the transforms cannot be finalized until the
+    // desktop compatibility viewport lands.
+
+    // We should never have just one pinch-zoom scrollbar.
+    DCHECK((m_horizontalPinchZoomScrollbarLayer && m_verticalPinchZoomScrollbarLayer) ||
+           (!m_horizontalPinchZoomScrollbarLayer && !m_verticalPinchZoomScrollbarLayer));
+
+    bool hasPinchZoomScrollbars = m_horizontalPinchZoomScrollbarLayer && m_verticalPinchZoomScrollbarLayer;
+
+    if (!hasPinchZoomScrollbars && (m_implTransform == transform))
         return;
 
-    m_implTransform = transform;
-    noteLayerPropertyChangedForSubtree();
+    bool redirectedToClipLayer = false;
+    if (hasPinchZoomScrollbars) {
+        gfx::Transform scrollbarTransformHorizontal(transform);
+        // TODO(wjmaclean) This is the wrong translation, need to
+        // know the offset of the desktop compatibility viewport.

[aelias_OOO_until_Jul13, 2013/02/06 19:02:45]

I gather you're trying to make the scrollbars visible near bottom or right
fixed-pos elements?  In the meantime, you could get something landable by
expanding the viewport by (1 / pageScaleFactor) and then clamp to edges, not
worrying too much about precise y scroll offset.

+        scrollbarTransformHorizontal.Translate(0, -layerTreeImpl()->device_scale_factor() * scrollOffset().y());
+        if (m_horizontalScrollbarLayer)
+            m_horizontalScrollbarLayer->setImplTransform(scrollbarTransformHorizontal);
+
+        gfx::Transform scrollbarTransformVertical(transform);
+        // TODO(wjmaclean) Same comment as above.
+        scrollbarTransformVertical.Translate(-layerTreeImpl()->device_scale_factor() * scrollOffset().x(), 0);
+        if (m_verticalScrollbarLayer)
+            m_verticalScrollbarLayer->setImplTransform(scrollbarTransformVertical);
+        // If we're using pinch-zoom scrollbars, we don't want them
+        // clipped to the untransformed bounds, so we re-direct
+        // the implTransform to the clip layer instead.
+        if (parent()) {
+            parent()->setImplTransform(transform);
+            redirectedToClipLayer = true;
+        }
+    }
+
+    if (!redirectedToClipLayer && m_implTransform != transform) {
+        m_implTransform = transform;
+        noteLayerPropertyChangedForSubtree();
+    }
 }
 
 void LayerImpl::setDoubleSided(bool doubleSided)
@@ -969,4 +1018,14 @@ void LayerImpl::setVerticalScrollbarLayer(ScrollbarLayerImpl* scrollbarLayer)
         m_verticalScrollbarLayer->setScrollLayerId(id());
 }
 
+void LayerImpl::setHorizontalPinchZoomScrollbarLayer(ScrollbarLayerImpl* scrollbarLayer)
+{
+    m_horizontalPinchZoomScrollbarLayer = scrollbarLayer;
+}
+
+void LayerImpl::setVerticalPinchZoomScrollbarLayer(ScrollbarLayerImpl* scrollbarLayer)
+{
+    m_verticalPinchZoomScrollbarLayer = scrollbarLayer;
+}
+
 }  // namespace cc