Viewport: Stop ongoing physical drag upon user interaction

An animated drag operation will now stop if the user interacts with
the content area again before the animation is finished. It is also
stopped if the user interacts with the scrollbars.

modules/juce_gui_basics/layout/juce_Viewport.cpp

@@ -61,6 +61,12 @@ struct Viewport::DragToScrollListener   : private MouseListener,
         Desktop::getInstance().removeGlobalMouseListener (this);
     }
 
+    void stopOngoingAnimation()
+    {
+        offsetX.setPosition (offsetX.getPosition());
+        offsetY.setPosition (offsetY.getPosition());
+    }
+
     void positionChanged (ViewportDragPosition&, double) override
     {
         viewport.setViewPosition (originalViewPos - Point<int> ((int) offsetX.getPosition(),
@@ -119,9 +125,11 @@ struct Viewport::DragToScrollListener   : private MouseListener,
 
     void endDragAndClearGlobalMouseListener()
     {
-        offsetX.endDrag();
-        offsetY.endDrag();
-        isDragging = false;
+        if (std::exchange (isDragging, false) == true)
+        {
+            offsetX.endDrag();
+            offsetY.endDrag();
+        }
 
         viewport.contentHolder.addMouseListener (this, true);
         Desktop::getInstance().removeGlobalMouseListener (this);
@@ -229,6 +237,8 @@ void Viewport::recreateScrollbars()
 
     getVerticalScrollBar().addListener (this);
     getHorizontalScrollBar().addListener (this);
+    getVerticalScrollBar().addMouseListener (this, true);
+    getHorizontalScrollBar().addMouseListener (this, true);
 
     resized();
 }
@@ -531,8 +541,15 @@ void Viewport::scrollBarMoved (ScrollBar* scrollBarThatHasMoved, double newRange
 
 void Viewport::mouseWheelMove (const MouseEvent& e, const MouseWheelDetails& wheel)
 {
-    if (! useMouseWheelMoveIfNeeded (e, wheel))
-        Component::mouseWheelMove (e, wheel);
+    if (e.eventComponent == this)
+        if (! useMouseWheelMoveIfNeeded (e, wheel))
+            Component::mouseWheelMove (e, wheel);
+}
+
+void Viewport::mouseDown (const MouseEvent& e)
+{
+    if (e.eventComponent == horizontalScrollBar.get() || e.eventComponent == verticalScrollBar.get())
+        dragToScrollListener->stopOngoingAnimation();
 }
 
 static int rescaleMouseWheelDistance (float distance, int singleStepSize) noexcept

modules/juce_gui_basics/layout/juce_Viewport.h

@@ -318,6 +318,8 @@ public:
     /** @internal */
     void mouseWheelMove (const MouseEvent&, const MouseWheelDetails&) override;
     /** @internal */
+    void mouseDown (const MouseEvent& e) override;
+    /** @internal */
     bool keyPressed (const KeyPress&) override;
     /** @internal */
     void componentMovedOrResized (Component&, bool wasMoved, bool wasResized) override;