File fix-slow-scrolling-in-dock-panels.patch of Package dolphin.5988

From 90beb4a5e37b887caad1e767046a42dad0af1ab3 Mon Sep 17 00:00:00 2001
From: Elvis Angelaccio <elvis.angelaccio@kde.org>
Date: Sun, 20 Nov 2016 12:21:29 +0100
Subject: 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
---
 src/kitemviews/kitemlistcontainer.cpp                |  2 +-
 src/kitemviews/kitemlistview.cpp                     |  5 +++++
 src/kitemviews/kitemlistview.h                       |  7 ++++++-
 src/kitemviews/private/kitemlistsizehintresolver.cpp | 13 +++++++++++++
 src/kitemviews/private/kitemlistsizehintresolver.h   |  2 ++
 5 files changed, 27 insertions(+), 2 deletions(-)

diff --git a/src/kitemviews/kitemlistcontainer.cpp b/src/kitemviews/kitemlistcontainer.cpp
index 6974ebb..6a0c575 100644
--- a/src/kitemviews/kitemlistcontainer.cpp
+++ b/src/kitemviews/kitemlistcontainer.cpp
@@ -265,7 +265,7 @@ void KItemListContainer::updateScrollOffsetScrollBar()
     if (view->scrollOrientation() == Qt::Vertical) {
         smoothScroller = m_verticalSmoothScroller;
         scrollOffsetScrollBar = verticalScrollBar();
-        singleStep = view->itemSize().height();
+        singleStep = view->itemSizeHint().height();
         // We cannot use view->size().height() because this height might
         // include the header widget, which is not part of the scrolled area.
         pageStep = view->verticalPageStep();
diff --git a/src/kitemviews/kitemlistview.cpp b/src/kitemviews/kitemlistview.cpp
index df65399..d840509 100644
--- a/src/kitemviews/kitemlistview.cpp
+++ b/src/kitemviews/kitemlistview.cpp
@@ -344,6 +344,11 @@ QSizeF KItemListView::itemSize() const
     return m_itemSize;
 }
 
+QSizeF KItemListView::itemSizeHint() const
+{
+    return m_sizeHintResolver->maxSizeHint();
+}
+
 const KItemListStyleOption& KItemListView::styleOption() const
 {
     return m_styleOption;
diff --git a/src/kitemviews/kitemlistview.h b/src/kitemviews/kitemlistview.h
index 9adf9f8..c93297c 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;
diff --git a/src/kitemviews/private/kitemlistsizehintresolver.cpp b/src/kitemviews/private/kitemlistsizehintresolver.cpp
index 1d80670..02f1865 100644
--- a/src/kitemviews/private/kitemlistsizehintresolver.cpp
+++ b/src/kitemviews/private/kitemlistsizehintresolver.cpp
@@ -25,6 +25,7 @@ KItemListSizeHintResolver::KItemListSizeHintResolver(const KItemListView* itemLi
     m_itemListView(itemListView),
     m_logicalHeightHintCache(),
     m_logicalWidthHint(0.0),
+    m_logicalHeightHint(0.0),
     m_needsResolving(false)
 {
 }
@@ -33,6 +34,12 @@ KItemListSizeHintResolver::~KItemListSizeHintResolver()
 {
 }
 
+QSizeF KItemListSizeHintResolver::maxSizeHint()
+{
+    updateCache();
+    return QSizeF(m_logicalWidthHint, m_logicalHeightHint);
+}
+
 QSizeF KItemListSizeHintResolver::sizeHint(int index)
 {
     updateCache();
@@ -149,6 +156,12 @@ void KItemListSizeHintResolver::updateCache()
 {
     if (m_needsResolving) {
         m_itemListView->calculateItemSizeHints(m_logicalHeightHintCache, m_logicalWidthHint);
+        // Set logical height as the max cached height (if the cache is not empty).
+        if (m_logicalHeightHintCache.isEmpty()) {
+            m_logicalHeightHint = 0.0;
+        } else {
+            m_logicalHeightHint = *std::max_element(m_logicalHeightHintCache.begin(), m_logicalHeightHintCache.end());
+        }
         m_needsResolving = false;
     }
 }
diff --git a/src/kitemviews/private/kitemlistsizehintresolver.h b/src/kitemviews/private/kitemlistsizehintresolver.h
index ff17f2d..841e9ca 100644
--- a/src/kitemviews/private/kitemlistsizehintresolver.h
+++ b/src/kitemviews/private/kitemlistsizehintresolver.h
@@ -36,6 +36,7 @@ class DOLPHIN_EXPORT KItemListSizeHintResolver
 public:
     KItemListSizeHintResolver(const KItemListView* itemListView);
     virtual ~KItemListSizeHintResolver();
+    QSizeF maxSizeHint();
     QSizeF sizeHint(int index);
 
     void itemsInserted(const KItemRangeList& itemRanges);
@@ -50,6 +51,7 @@ private:
     const KItemListView* m_itemListView;
     mutable QVector<qreal> m_logicalHeightHintCache;
     mutable qreal m_logicalWidthHint;
+    mutable qreal m_logicalHeightHint;
     bool m_needsResolving;
 };
 
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