2009-04-16 Peter Kasting <pkasting@google.com>

        Reviewed by David Hyatt.

        https://bugs.webkit.org/show_bug.cgi?id=25250
        Allow platforms to snap the scroll thumb back to the drag origin
        during a drag.  Implement functions for Safari/Win and Chromium/Win
        to do this snapping at distances approximating the native ones.

        * platform/Scrollbar.cpp:
        (WebCore::Scrollbar::Scrollbar):
        (WebCore::Scrollbar::setValue):
        (WebCore::Scrollbar::scroll):
        (WebCore::Scrollbar::moveThumb):
        (WebCore::Scrollbar::setCurrentPos):
        (WebCore::Scrollbar::mouseMoved):
        (WebCore::Scrollbar::mouseDown):
        * platform/Scrollbar.h:
        * platform/ScrollbarTheme.h:
        (WebCore::ScrollbarTheme::shouldSnapBackToDragOrigin):
        * platform/chromium/ScrollbarThemeChromium.h:
        * platform/chromium/ScrollbarThemeChromiumLinux.cpp:
        (WebCore::ScrollbarThemeChromium::shouldSnapBackToDragOrigin):
        * platform/chromium/ScrollbarThemeChromiumWin.cpp:
        (WebCore::ScrollbarThemeChromium::shouldSnapBackToDragOrigin):
        * platform/win/ScrollbarThemeWin.cpp:
        (WebCore::ScrollbarThemeWin::shouldCenterOnThumb):
        (WebCore::ScrollbarThemeWin::shouldSnapBackToDragOrigin):
        * platform/win/ScrollbarThemeWin.h:



git-svn-id: svn://svn.chromium.org/blink/trunk@42721 bbb929c8-8fbe-4397-9dbb-9b2b20218538

third_party/WebKit/WebCore/ChangeLog

+2009-04-16  Peter Kasting  <pkasting@google.com>
+
+        Reviewed by David Hyatt.
+
+        https://bugs.webkit.org/show_bug.cgi?id=25250
+        Allow platforms to snap the scroll thumb back to the drag origin
+        during a drag.  Implement functions for Safari/Win and Chromium/Win
+        to do this snapping at distances approximating the native ones.
+
+        * platform/Scrollbar.cpp:
+        (WebCore::Scrollbar::Scrollbar):
+        (WebCore::Scrollbar::setValue):
+        (WebCore::Scrollbar::scroll):
+        (WebCore::Scrollbar::moveThumb):
+        (WebCore::Scrollbar::setCurrentPos):
+        (WebCore::Scrollbar::mouseMoved):
+        (WebCore::Scrollbar::mouseDown):
+        * platform/Scrollbar.h:
+        * platform/ScrollbarTheme.h:
+        (WebCore::ScrollbarTheme::shouldSnapBackToDragOrigin):
+        * platform/chromium/ScrollbarThemeChromium.h:
+        * platform/chromium/ScrollbarThemeChromiumLinux.cpp:
+        (WebCore::ScrollbarThemeChromium::shouldSnapBackToDragOrigin):
+        * platform/chromium/ScrollbarThemeChromiumWin.cpp:
+        (WebCore::ScrollbarThemeChromium::shouldSnapBackToDragOrigin):
+        * platform/win/ScrollbarThemeWin.cpp:
+        (WebCore::ScrollbarThemeWin::shouldCenterOnThumb):
+        (WebCore::ScrollbarThemeWin::shouldSnapBackToDragOrigin):
+        * platform/win/ScrollbarThemeWin.h:
+
 2009-04-21  Adam Roben  <aroben@apple.com>
 
         Windows build fix

third_party/WebKit/WebCore/platform/Scrollbar.cpp

@@ -57,6 +57,7 @@ Scrollbar::Scrollbar(ScrollbarClient* client, ScrollbarOrientation orientation,
     , m_visibleSize(0)
     , m_totalSize(0)
     , m_currentPos(0)
+    , m_dragOrigin(0)
     , m_lineStep(0)
     , m_pageStep(0)
     , m_pixelStep(1)
@@ -92,13 +93,7 @@ bool Scrollbar::setValue(int v)
     v = max(min(v, m_totalSize - m_visibleSize), 0);
     if (value() == v)
         return false; // Our value stayed the same.
-    m_currentPos = v;
-
-    updateThumbPosition();
-
-    if (client())
-        client()->valueChanged(this);
-    
+    setCurrentPos(v);
     return true;
 }
 
@@ -139,20 +134,7 @@ bool Scrollbar::scroll(ScrollDirection direction, ScrollGranularity granularity,
         
     float newPos = m_currentPos + step * multiplier;
     float maxPos = m_totalSize - m_visibleSize;
-    newPos = max(min(newPos, maxPos), 0.0f);
-
-    if (newPos == m_currentPos)
-        return false;
-    
-    int oldValue = value();
-    m_currentPos = newPos;
-    updateThumbPosition();
-    
-    if (value() != oldValue && client())
-        client()->valueChanged(this);
-    
-    // return true even if the integer value did not change so that scroll event gets eaten
-    return true;
+    return setCurrentPos(max(min(newPos, maxPos), 0.0f));
 }
 
 void Scrollbar::updateThumbPosition()
@@ -269,15 +251,30 @@ void Scrollbar::moveThumb(int pos)
     int thumbLen = theme()->thumbLength(this);
     int trackLen = theme()->trackLength(this);
     int maxPos = trackLen - thumbLen;
-    int delta = pos - pressedPos();
+    int delta = pos - m_pressedPos;
     if (delta > 0)
         delta = min(maxPos - thumbPos, delta);
     else if (delta < 0)
         delta = max(-thumbPos, delta);
-    if (delta) {
-        setValue(static_cast<int>(static_cast<float>(thumbPos + delta) * maximum() / (trackLen - thumbLen)));
-        setPressedPos(pressedPos() + theme()->thumbPosition(this) - thumbPos);
-    }
+    if (delta)
+        setCurrentPos(static_cast<float>(thumbPos + delta) * maximum() / (trackLen - thumbLen));
+}
+
+bool Scrollbar::setCurrentPos(float pos)
+{
+    if (pos == m_currentPos)
+        return false;
+
+    int oldValue = value();
+    int oldThumbPos = theme()->thumbPosition(this);
+    m_currentPos = pos;
+    updateThumbPosition();
+    if (m_pressedPart == ThumbPart)
+        setPressedPos(m_pressedPos + theme()->thumbPosition(this) - oldThumbPos);
+
+    if (value() != oldValue && client())
+        client()->valueChanged(this);
+    return true;
 }
 
 void Scrollbar::setHoveredPart(ScrollbarPart part)
@@ -308,9 +305,13 @@ void Scrollbar::setPressedPart(ScrollbarPart part)
 bool Scrollbar::mouseMoved(const PlatformMouseEvent& evt)
 {
     if (m_pressedPart == ThumbPart) {
-        moveThumb(m_orientation == HorizontalScrollbar ? 
-                  convertFromContainingWindow(evt.pos()).x() :
-                  convertFromContainingWindow(evt.pos()).y());
+        if (theme()->shouldSnapBackToDragOrigin(this, evt))
+            setCurrentPos(m_dragOrigin);
+        else {
+            moveThumb(m_orientation == HorizontalScrollbar ? 
+                      convertFromContainingWindow(evt.pos()).x() :
+                      convertFromContainingWindow(evt.pos()).y());
+        }
         return true;
     }
 
@@ -366,9 +367,10 @@ bool Scrollbar::mouseDown(const PlatformMouseEvent& evt)
     setPressedPart(theme()->hitTest(this, evt));
     int pressedPos = (orientation() == HorizontalScrollbar ? convertFromContainingWindow(evt.pos()).x() : convertFromContainingWindow(evt.pos()).y());
     
-    if ((pressedPart() == BackTrackPart || pressedPart() == ForwardTrackPart) && theme()->shouldCenterOnThumb(this, evt)) {
+    if ((m_pressedPart == BackTrackPart || m_pressedPart == ForwardTrackPart) && theme()->shouldCenterOnThumb(this, evt)) {
         setHoveredPart(ThumbPart);
         setPressedPart(ThumbPart);
+        m_dragOrigin = m_currentPos;
         int thumbLen = theme()->thumbLength(this);
         int desiredPos = pressedPos;
         // Set the pressed position to the middle of the thumb so that when we do the move, the delta
@@ -376,7 +378,8 @@ bool Scrollbar::mouseDown(const PlatformMouseEvent& evt)
         m_pressedPos = theme()->trackPosition(this) + theme()->thumbPosition(this) + thumbLen / 2;
         moveThumb(desiredPos);
         return true;
-    }
+    } else if (m_pressedPart == ThumbPart)
+        m_dragOrigin = m_currentPos;
     
     m_pressedPos = pressedPos;
 

third_party/WebKit/WebCore/platform/Scrollbar.h

@@ -137,6 +137,7 @@ protected:
     ScrollGranularity pressedPartScrollGranularity();
     
     void moveThumb(int pos);
+    bool setCurrentPos(float pos);
 
     ScrollbarClient* m_client;
     ScrollbarOrientation m_orientation;
@@ -146,6 +147,7 @@ protected:
     int m_visibleSize;
     int m_totalSize;
     float m_currentPos;
+    float m_dragOrigin;
     int m_lineStep;
     int m_pageStep;
     float m_pixelStep;

third_party/WebKit/WebCore/platform/ScrollbarTheme.h

@@ -76,6 +76,7 @@ public:
     virtual void paintScrollCorner(ScrollView*, GraphicsContext* context, const IntRect& cornerRect) { context->fillRect(cornerRect, Color::white); }
 
     virtual bool shouldCenterOnThumb(Scrollbar*, const PlatformMouseEvent&) { return false; }
+    virtual bool shouldSnapBackToDragOrigin(Scrollbar*, const PlatformMouseEvent&) { return false; }
     virtual int thumbPosition(Scrollbar*) { return 0; } // The position of the thumb relative to the track.
     virtual int thumbLength(Scrollbar*) { return 0; } // The length of the thumb along the axis of the scrollbar.
     virtual int trackPosition(Scrollbar*) { return 0; } // The position of the track relative to the scrollbar.

third_party/WebKit/WebCore/platform/chromium/ScrollbarThemeChromium.h

@@ -63,6 +63,7 @@ namespace WebCore {
 
         virtual void paintScrollCorner(ScrollView*, GraphicsContext*, const IntRect&);
         virtual bool shouldCenterOnThumb(Scrollbar*, const PlatformMouseEvent&);
+        virtual bool shouldSnapBackToDragOrigin(Scrollbar*, const PlatformMouseEvent&);
 
         virtual void paintTrackBackground(GraphicsContext*, Scrollbar*, const IntRect&);
         virtual void paintTrackPiece(GraphicsContext*, Scrollbar*, const IntRect&, ScrollbarPart);

third_party/WebKit/WebCore/platform/chromium/ScrollbarThemeChromiumLinux.cpp

@@ -72,6 +72,11 @@ static void drawBox(SkCanvas* canvas, const IntRect& rect, const SkPaint& paint)
     drawVertLine(canvas, rect.x(), rect.y(), bottom, paint);
 }
 
+bool ScrollbarThemeChromium::shouldSnapBackToDragOrigin(Scrollbar*, const PlatformMouseEvent&)
+{
+    return false;
+}
+
 void ScrollbarThemeChromium::paintTrackPiece(GraphicsContext* gc, Scrollbar* scrollbar,
                                              const IntRect& rect, ScrollbarPart partType)
 {

third_party/WebKit/WebCore/platform/chromium/ScrollbarThemeChromiumWin.cpp

@@ -44,6 +44,13 @@ namespace WebCore {
 // Metrics obtained using [NSScroller scrollerWidthForControlSize:]
 static const int kMacScrollbarSize[3] = { 15, 11, 15 };
 
+// Constants used to figure the drag rect outside which we should snap the
+// scrollbar thumb back to its origin.  These calculations are based on
+// observing the behavior of the MSVC8 main window scrollbar + some
+// guessing/extrapolation.
+static const int kOffEndMultiplier = 3;
+static const int kOffSideMultiplier = 8;
+
 int ScrollbarThemeChromium::scrollbarThickness(ScrollbarControlSize controlSize)
 {
     static int thickness;
@@ -60,6 +67,24 @@ bool ScrollbarThemeChromium::invalidateOnMouseEnterExit()
     return isVistaOrNewer();
 }
 
+bool ScrollbarThemeChromium::shouldSnapBackToDragOrigin(Scrollbar* scrollbar, const PlatformMouseEvent& evt)
+{
+    // Find the rect within which we shouldn't snap, by expanding the track rect
+    // in both dimensions.
+    IntRect rect = trackRect(scrollbar);
+    const bool horz = scrollbar->orientation() == HorizontalScrollbar;
+    const int thickness = scrollbarThickness(scrollbar->controlSize());
+    rect.inflateX((horz ? kOffEndMultiplier : kOffSideMultiplier) * thickness);
+    rect.inflateY((horz ? kOffSideMultiplier : kOffEndMultiplier) * thickness);
+
+    // Convert the event to local coordinates.
+    IntPoint mousePosition = scrollbar->convertFromContainingWindow(evt.pos());
+    mousePosition.move(scrollbar->x(), scrollbar->y());
+
+    // We should snap iff the event is outside our calculated rect.
+    return !rect.contains(mousePosition);
+}
+
 void ScrollbarThemeChromium::paintTrackPiece(GraphicsContext* gc, Scrollbar* scrollbar, const IntRect& rect, ScrollbarPart partType)
 {
     bool horz = scrollbar->orientation() == HorizontalScrollbar;

third_party/WebKit/WebCore/platform/win/ScrollbarThemeWin.cpp

@@ -72,6 +72,13 @@ SOFT_LINK(uxtheme, DrawThemeBackground, HRESULT, WINAPI, (HANDLE hTheme, HDC hdc
 SOFT_LINK(uxtheme, IsThemeActive, BOOL, WINAPI, (), ())
 SOFT_LINK(uxtheme, IsThemeBackgroundPartiallyTransparent, BOOL, WINAPI, (HANDLE hTheme, int iPartId, int iStateId), (hTheme, iPartId, iStateId))
 
+// Constants used to figure the drag rect outside which we should snap the
+// scrollbar thumb back to its origin.  These calculations are based on
+// observing the behavior of the MSVC8 main window scrollbar + some
+// guessing/extrapolation.
+static const int kOffEndMultiplier = 3;
+static const int kOffSideMultiplier = 8;
+
 static void checkAndInitScrollbarTheme()
 {
     if (uxthemeLibrary() && !scrollbarTheme && IsThemeActive())
@@ -180,6 +187,29 @@ IntRect ScrollbarThemeWin::trackRect(Scrollbar* scrollbar, bool)
     return IntRect(scrollbar->x(), scrollbar->y() + thickness, thickness, scrollbar->height() - 2 * thickness);
 }
 
+bool ScrollbarThemeWin::shouldCenterOnThumb(Scrollbar*, const PlatformMouseEvent& evt)
+{
+    return evt.shiftKey() && evt.button() == LeftButton;
+}
+
+bool ScrollbarThemeWin::shouldSnapBackToDragOrigin(Scrollbar* scrollbar, const PlatformMouseEvent& evt)
+{
+    // Find the rect within which we shouldn't snap, by expanding the track rect
+    // in both dimensions.
+    IntRect rect = trackRect(scrollbar);
+    const bool horz = scrollbar->orientation() == HorizontalScrollbar;
+    const int thickness = scrollbarThickness(scrollbar->controlSize());
+    rect.inflateX((horz ? kOffEndMultiplier : kOffSideMultiplier) * thickness);
+    rect.inflateY((horz ? kOffSideMultiplier : kOffEndMultiplier) * thickness);
+
+    // Convert the event to local coordinates.
+    IntPoint mousePosition = scrollbar->convertFromContainingWindow(evt.pos());
+    mousePosition.move(scrollbar->x(), scrollbar->y());
+
+    // We should snap iff the event is outside our calculated rect.
+    return !rect.contains(mousePosition);
+}
+
 void ScrollbarThemeWin::paintTrackBackground(GraphicsContext* context, Scrollbar* scrollbar, const IntRect& rect)
 {
     // Just assume a forward track part.  We only paint the track as a single piece when there is no thumb.
@@ -340,10 +370,5 @@ void ScrollbarThemeWin::paintThumb(GraphicsContext* context, Scrollbar* scrollba
     context->releaseWindowsContext(hdc, rect, alphaBlend);
 }
 
-bool ScrollbarThemeWin::shouldCenterOnThumb(Scrollbar*, const PlatformMouseEvent& evt)
-{
-    return evt.shiftKey() && evt.button() == LeftButton;
-}
-
 }
 

third_party/WebKit/WebCore/platform/win/ScrollbarThemeWin.h

@@ -50,6 +50,7 @@ protected:
     virtual IntRect trackRect(Scrollbar*, bool painting = false);
 
     virtual bool shouldCenterOnThumb(Scrollbar*, const PlatformMouseEvent&);
+    virtual bool shouldSnapBackToDragOrigin(Scrollbar*, const PlatformMouseEvent&);
 
     virtual void paintTrackBackground(GraphicsContext*, Scrollbar*, const IntRect&);
     virtual void paintTrackPiece(GraphicsContext*, Scrollbar*, const IntRect&, ScrollbarPart);