BListView: Add ScrollTo(index) method, auto-scroll on drag

Multi-select lists may also auto-scroll on drag now as well.

Document ScrollTo(index). Give Scrolling its own section.

Change-Id: I36284a28376a01bafd23ddb30162fc786fb41521
Reviewed-on: https://review.haiku-os.org/c/haiku/+/7213
Tested-by: Commit checker robot <no-reply+buildbot@haiku-os.org>
Reviewed-by: Adrien Destugues <pulkomandy@pulkomandy.tk>

docs/user/interface/ListView.dox

@@ -461,6 +461,14 @@
 */
 
 
+/*!
+	\name Scrolling
+*/
+
+
+//! @{
+
+
 /*!
 	\fn void BListView::ScrollTo(BPoint point)
 	\brief Scroll the view to the specified \a point.
@@ -473,6 +481,30 @@
 */
 
 
+/*!
+	\fn void BListView::ScrollTo(int32 index)
+	\brief Scrolls to list item at \a index.
+
+	If above top scroll to first item, if below bottom
+	scroll to last item otherwise scroll to item at \a index.
+
+	\see IndexOf(), MouseMoved(), ScrollToSelection()
+
+	\since Haiku R1
+*/
+
+
+/*!
+	\fn void BListView::ScrollToSelection()
+	\brief Scrolls to selected list item.
+
+	\since BeOS R3
+*/
+
+
+//! @}
+
+
 /*!
 	\name Adding/Removing Items
 */
@@ -844,14 +876,6 @@
 //! @{
 
 
-/*!
-	\fn void BListView::ScrollToSelection()
-	\brief Scrolls to selected list item.
-
-	\since BeOS R3
-*/
-
-
 /*!
 	\fn void BListView::Select(int32 index, bool extend)
 	\brief Selects the list item at the specified \a index.

headers/os/interface/ListView.h

@@ -110,6 +110,7 @@ public:
 									void* arg), void* arg);
 			const BListItem**	Items() const;
 			void				InvalidateItem(int32 index);
+			void				ScrollTo(int32 index);
 			void				ScrollToSelection();
 
 			void				Select(int32 index, bool extend = false);

src/kits/interface/ListView.cpp

@@ -726,21 +726,26 @@ BListView::MouseMoved(BPoint where, uint32 code, const BMessage* dragMessage)
 			currentMessage->FindInt32("buttons", &buttons);
 	}
 
-	// only update selection if mouse button pressed and not dragging
 	int32 index = IndexOf(where);
-	if (buttons == 0 || fTrack->is_dragging)
-		return BView::MouseMoved(where, code, dragMessage);
-
-	// scroll to selection while button is pressed
-	ScrollToSelection();
-
-	// selection updating on drag is for single selection lists only
-	if (fListType == B_MULTIPLE_SELECTION_LIST || index == -1)
-		return BView::MouseMoved(where, code, dragMessage);
+	if (index == -1) {
+		// If where is above top, scroll to the first item,
+		// else if where is below bottom scroll to the last item.
+		if (where.y < Bounds().top)
+			index = 0;
+		else if (where.y > Bounds().bottom)
+			index = CountItems() - 1;
+	}
 
+	// don't scroll if button not pressed, no selection or same item
 	int32 lastIndex = fFirstSelected;
-	if (lastIndex != -1 && index != lastIndex) {
-		// mouse moved over unselected, fake selection until mouse up
+	if (buttons == 0 || index == -1 || lastIndex == -1 || index == lastIndex)
+		return BView::MouseMoved(where, code, dragMessage);
+
+	// scroll to item under mouse while button is pressed
+	ScrollTo(index);
+
+	if (!fTrack->is_dragging && fListType != B_MULTIPLE_SELECTION_LIST) {
+		// mouse moved over unselected item, fake selection until mouse up
 		ItemAt(lastIndex)->Deselect();
 		ItemAt(index)->Select();
 
@@ -749,7 +754,8 @@ BListView::MouseMoved(BPoint where, uint32 code, const BMessage* dragMessage)
 
 		// redraw items whose selection has changed
 		Invalidate(ItemFrame(lastIndex) | ItemFrame(index));
-	}
+	} else
+		Invalidate();
 
 	BView::MouseMoved(where, code, dragMessage);
 }
@@ -1199,6 +1205,23 @@ BListView::InvalidateItem(int32 index)
 }
 
 
+void
+BListView::ScrollTo(int32 index)
+{
+	if (index < 0)
+		index = 0;
+	if (index > CountItems() - 1)
+		index = CountItems() - 1;
+
+	BRect itemFrame = ItemFrame(index);
+	BRect bounds = Bounds();
+	if (itemFrame.top < bounds.top)
+		ScrollTo(itemFrame.LeftTop());
+	else if (itemFrame.bottom > bounds.bottom)
+		ScrollTo(BPoint(0, itemFrame.bottom - bounds.Height()));
+}
+
+
 void
 BListView::ScrollToSelection()
 {