Allow objects without scrollbars to be scrollable

Source/core/platform/ScrollableArea.cpp

 /*
  * Copyright (c) 2010, Google Inc. All rights reserved.
  * Copyright (C) 2008, 2011 Apple 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.
@@ skipping 76 matching lines @@
     ScrollbarOrientation orientation;
     Scrollbar* scrollbar;
     if (direction == ScrollUp || direction == ScrollDown) {
         orientation = VerticalScrollbar;
         scrollbar = verticalScrollbar();
     } else {
         orientation = HorizontalScrollbar;
         scrollbar = horizontalScrollbar();
     }
 
-    if (!scrollbar)
+    if (!isScrollable(orientation))
         return false;
 
     float step = 0;
-    switch (granularity) {
-    case ScrollByLine:
-        step = scrollbar->lineStep();
-        break;
-    case ScrollByPage:
-        step = scrollbar->pageStep();
-        break;
-    case ScrollByDocument:
-        step = scrollbar->totalSize();
-        break;
-    case ScrollByPixel:
-    case ScrollByPrecisePixel:
-        step = scrollbar->pixelStep();
-        break;
+
+    if (scrollbar) {
+        switch (granularity) {
+        case ScrollByLine:
+            step = scrollbar->lineStep();
+            break;
+        case ScrollByPage:
+            step = scrollbar->pageStep();
+            break;
+        case ScrollByDocument:
+            step = scrollbar->totalSize();
+            break;
+        case ScrollByPixel:
+        case ScrollByPrecisePixel:
+            step = scrollbar->pixelStep();
+            break;
+        }
+    } else {
+        // TODO: Where should we get the step sizes here?

[aelias_OOO_until_Jul13, 2013/06/18 00:54:47]

It looks like the step sizes should be moved out of the scrollbar object as
well.  How about making them part of the ScrollableArea?

[bokan, 2013/06/18 23:03:27]

Done, though ScrollableArea has a compile time assert about keeping its size
small. Is it ok that we're adding 24 bytes to the class size?

[aelias_OOO_until_Jul13, 2013/06/19 02:55:24]

Ah, no, that's not okay, sorry about that suggestion.

It looks like we could make the "step" information virtual getters in
ScrollableArea and have the subclasses implement them.  We could avoid separate
storage entirely and compute them on the fly in the getters.

[bokan, 2013/06/19 18:57:00]

Done.

+        switch (granularity) {
+        case ScrollByLine:
+        case ScrollByPage:
+        case ScrollByDocument:
+        case ScrollByPixel:
+        case ScrollByPrecisePixel:
+            step = 1.0f;
+            break;
+        }
     }
 
     if (direction == ScrollUp || direction == ScrollLeft)
         multiplier = -multiplier;
 
     return scrollAnimator()->scroll(orientation, granularity, step, multiplier);
 }
 
 void ScrollableArea::scrollToOffsetWithoutAnimation(const FloatPoint& offset)
 {
@@ skipping 232 matching lines @@
 {
     return layerForScrollCorner();
 }
 
 void ScrollableArea::serviceScrollAnimations()
 {
     if (ScrollAnimator* scrollAnimator = existingScrollAnimator())
         scrollAnimator->serviceScrollAnimations();
 }
 
-IntPoint ScrollableArea::scrollPosition() const
-{
-    int x = horizontalScrollbar() ? horizontalScrollbar()->value() : 0;
-    int y = verticalScrollbar() ? verticalScrollbar()->value() : 0;
-    return IntPoint(x, y);
-}
-
 IntPoint ScrollableArea::minimumScrollPosition() const
 {
     return IntPoint();
 }
 
 IntPoint ScrollableArea::maximumScrollPosition() const
 {
     return IntPoint(contentsSize().width() - visibleWidth(), contentsSize().height() - visibleHeight());
 }
 
@@ skipping 20 matching lines @@
     return scrollPosition.shrunkTo(maximumScrollPosition()).expandedTo(minimumScrollPosition());
 }
 
 void ScrollableArea::reportMemoryUsage(MemoryObjectInfo* memoryObjectInfo) const
 {
     MemoryClassInfo info(memoryObjectInfo, this);
     info.addMember(m_scrollAnimator, "scrollAnimator");
 }
 
 } // namespace WebCore