Blink Support for Overlay Scrollbar Animation

Source/platform/scroll/ScrollbarThemeOverlay.cpp

 /*
  * Copyright (C) 2011 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
@@ skipping 18 matching lines @@
 #include "platform/PlatformMouseEvent.h"
 #include "platform/graphics/GraphicsContext.h"
 #include "platform/scroll/ScrollbarThemeClient.h"
 #include "platform/transforms/TransformationMatrix.h"
 #include "public/platform/Platform.h"
 #include "public/platform/WebRect.h"
 #include "public/platform/WebThemeEngine.h"
 
 #include <algorithm>
 
+namespace {
+
+const int kDefaultOverlayScrollbarMinThumbThickness = 9;
+
+} // namespace
+
 namespace blink {
 
 ScrollbarThemeOverlay::ScrollbarThemeOverlay(int thumbThickness, int scrollbarMargin, HitTestBehavior allowHitTest, Color color)
     : ScrollbarTheme()
     , m_thumbThickness(thumbThickness)
     , m_scrollbarMargin(scrollbarMargin)
     , m_allowHitTest(allowHitTest)
     , m_color(color)
     , m_useSolidColor(true)
 {
@@ skipping 80 matching lines @@
         thumbRect.setWidth(thumbRect.width() - m_scrollbarMargin);
         if (scrollbar->isLeftSideVerticalScrollbar())
             thumbRect.setX(thumbRect.x() + m_scrollbarMargin);
     }
 
     if (m_useSolidColor) {
         context->fillRect(thumbRect, m_color);
         return;
     }
 
-    blink::WebThemeEngine::State state = blink::WebThemeEngine::StateNormal;
-    if (scrollbar->pressedPart() == ThumbPart)
-        state = blink::WebThemeEngine::StatePressed;
-    else if (scrollbar->hoveredPart() == ThumbPart)
-        state = blink::WebThemeEngine::StateHover;
-
     blink::WebCanvas* canvas = context->canvas();
 
     blink::WebThemeEngine::Part part = blink::WebThemeEngine::PartScrollbarHorizontalThumb;
     if (scrollbar->orientation() == VerticalScrollbar)
         part = blink::WebThemeEngine::PartScrollbarVerticalThumb;
 
-    blink::Platform::current()->themeEngine()->paint(canvas, part, state, blink::WebRect(rect), 0);
+    if (scrollbar->isDuringStateTransitionAnimation()) {
+        // Paint in between of two states. First get information from ScrollAnimator
+        double progress = scrollbar->stateTransitionProgress();
+        blink::WebThemeEngine::State startState = scrollbar->stateTransitionStartState();
+        blink::WebThemeEngine::State endState = scrollbar->stateTransitionEndState();
+        double thumbThicknessChanged = progress * (m_thumbThickness - kDefaultOverlayScrollbarMinThumbThickness);
+        double disThumbThickness = m_thumbThickness - thumbThicknessChanged;
+        int displayedThumbThickness = static_cast<int>(disThumbThickness);
+        if (startState == blink::WebThemeEngine::StateNormal)
+            displayedThumbThickness = kDefaultOverlayScrollbarMinThumbThickness + thumbThicknessChanged;
+
+        if (scrollbar->orientation() == HorizontalScrollbar) {
+            thumbRect.setY(thumbRect.y() + (m_thumbThickness - displayedThumbThickness));
+            thumbRect.setHeight(displayedThumbThickness);
+        } else {
+            thumbRect.setWidth(displayedThumbThickness);
+            if (!scrollbar->isLeftSideVerticalScrollbar())
+                thumbRect.setX(thumbRect.x() + (m_thumbThickness - displayedThumbThickness));
+        }
+
+        //        int testThumbThickness = static_cast<int>(displayedThumbThickness);
+        // thumbRect.setWidth(1);
+
+        blink::Platform::current()->themeEngine()->paintStateTransition(canvas, part, startState, endState, progress, blink::WebRect(thumbRect));
+        return;
+    }
+
+    blink::WebThemeEngine::State state = blink::WebThemeEngine::StateNormal;
+    if (scrollbar->pressedPart() == ThumbPart) {
+        state = blink::WebThemeEngine::StatePressed;
+    } else if (scrollbar->hoveredPart() == ThumbPart) {
+        state = blink::WebThemeEngine::StateHover;
+    } else {
+        if (scrollbar->orientation() == HorizontalScrollbar) {
+            thumbRect.setY(thumbRect.y() + (m_thumbThickness - kDefaultOverlayScrollbarMinThumbThickness));
+            thumbRect.setHeight(kDefaultOverlayScrollbarMinThumbThickness);
+        } else {
+            thumbRect.setWidth(kDefaultOverlayScrollbarMinThumbThickness);
+            if (!scrollbar->isLeftSideVerticalScrollbar())
+                thumbRect.setX(thumbRect.x() + (m_thumbThickness - kDefaultOverlayScrollbarMinThumbThickness));
+        }
+    }
+
+    blink::Platform::current()->themeEngine()->paint(canvas, part, state, blink::WebRect(thumbRect), 0);
 }
 
 ScrollbarPart ScrollbarThemeOverlay::hitTest(ScrollbarThemeClient* scrollbar, const IntPoint& position)
 {
     if (m_allowHitTest == DisallowHitTest)
         return NoPart;
 
     return ScrollbarTheme::hitTest(scrollbar, position);
 }
 
 } // namespace blink