Fix slow scrolling in dock panels

Commit f688bcd1f1 fixed slow scrolling with xf86-input-libinput on DolphinView.

However the commit also exposed a bug in the Dolphin scrolling
algorithm, which was previously hidden. This resulted in slow
scrolling in dock panels (Places and Folders), with both
xf86-input-evdev and xf86-input-libinput drivers, as well as libinput on
Wayland.

KItemListContainer::updateScrollOffsetScrollBar() relied on the view's
itemSize() method to compute the scrollbar's singleStep, but this QSize
was invalid for the dock panels' views.

We use a new itemSizeHint() method instead, which is always valid and
also adapts to the current icon size set in the view.

BUG: 365968
FIXED-IN: 16.12.0
REVIEW: 129409

1 files changed, 6 insertions, 1 deletions

diff --git a/src/kitemviews/kitemlistview.h b/src/kitemviews/kitemlistview.h
index 9adf9f86f..c93297c47 100644
--- a/src/kitemviews/kitemlistview.h
+++ b/src/kitemviews/kitemlistview.h
@@ -154,10 +154,15 @@ public:
 
     /**
      * @return The basic size of all items. The size of an item may be larger than
-     *         the basic size (see KItemListView::itemSizeHint() and KItemListView::itemRect()).
+     *         the basic size (see KItemListView::itemRect()).
      */
     QSizeF itemSize() const;
 
+    /**
+     * @return The size hint of all items. It is provided by the KItemListSizeHintResolver.
+     */
+    QSizeF itemSizeHint() const;
+
     const KItemListStyleOption& styleOption() const;
 
     virtual void setGeometry(const QRectF& rect) Q_DECL_OVERRIDE;