From 0b130dd57e594d7433141483aa162e4414a9d07b Mon Sep 17 00:00:00 2001
From: Marco Martin <notmart@gmail.com>
Date: Mon, 29 Jan 2018 11:52:23 +0100
Subject: [PATCH] base scrolling on the smallest item

Summary:
CCBUG: 386379

after recent highdpi patches on scrolling that delegated it
completely to the scrollbar, based upon the scrollbar singleStep
setted to the tallest of the items in the view.
tough this makes scrolling way too fast, and on folders where just
few filenames are longer than most we can get a single scrolling
step almost double the number of lines configured in the
mouse kcm.
Using the shortest item instead of the tallest mitigates this problem
making it a bit more usable

Test Plan:
tested on different folders in different view modes both with
mouse and touchpad

Reviewers: #dolphin, broulik, ngraham

Reviewed By: #dolphin, ngraham

Subscribers: ngraham, plasma-devel

Tags: #plasma

Differential Revision: https://phabricator.kde.org/D10102
---
 src/kitemviews/kitemlistcontainer.cpp                | 1 -
 src/kitemviews/kitemlistview.cpp                     | 2 +-
 src/kitemviews/private/kitemlistsizehintresolver.cpp | 8 ++++++++
 src/kitemviews/private/kitemlistsizehintresolver.h   | 2 ++
 4 files changed, 11 insertions(+), 2 deletions(-)

diff --git a/src/kitemviews/kitemlistcontainer.cpp b/src/kitemviews/kitemlistcontainer.cpp
index 8e64ee4933..c1eae53bd6 100644
--- a/src/kitemviews/kitemlistcontainer.cpp
+++ b/src/kitemviews/kitemlistcontainer.cpp
@@ -35,7 +35,6 @@
 #include <QStyle>
 #include <QStyleOption>
 
-
 /**
  * Replaces the default viewport of KItemListContainer by a
  * non-scrollable viewport. The scrolling is done in an optimized
diff --git a/src/kitemviews/kitemlistview.cpp b/src/kitemviews/kitemlistview.cpp
index 71091033c9..dbeb571a40 100644
--- a/src/kitemviews/kitemlistview.cpp
+++ b/src/kitemviews/kitemlistview.cpp
@@ -342,7 +342,7 @@ QSizeF KItemListView::itemSize() const
 
 QSizeF KItemListView::itemSizeHint() const
 {
-    return m_sizeHintResolver->maxSizeHint();
+    return m_sizeHintResolver->minSizeHint();
 }
 
 const KItemListStyleOption& KItemListView::styleOption() const
diff --git a/src/kitemviews/private/kitemlistsizehintresolver.cpp b/src/kitemviews/private/kitemlistsizehintresolver.cpp
index 02f1865b34..5c121c6670 100644
--- a/src/kitemviews/private/kitemlistsizehintresolver.cpp
+++ b/src/kitemviews/private/kitemlistsizehintresolver.cpp
@@ -26,6 +26,7 @@ KItemListSizeHintResolver::KItemListSizeHintResolver(const KItemListView* itemLi
     m_logicalHeightHintCache(),
     m_logicalWidthHint(0.0),
     m_logicalHeightHint(0.0),
+    m_minHeightHint(0.0),
     m_needsResolving(false)
 {
 }
@@ -40,6 +41,12 @@ QSizeF KItemListSizeHintResolver::maxSizeHint()
     return QSizeF(m_logicalWidthHint, m_logicalHeightHint);
 }
 
+QSizeF KItemListSizeHintResolver::minSizeHint()
+{
+    updateCache();
+    return QSizeF(m_logicalWidthHint, m_minHeightHint);
+}
+
 QSizeF KItemListSizeHintResolver::sizeHint(int index)
 {
     updateCache();
@@ -161,6 +168,7 @@ void KItemListSizeHintResolver::updateCache()
             m_logicalHeightHint = 0.0;
         } else {
             m_logicalHeightHint = *std::max_element(m_logicalHeightHintCache.begin(), m_logicalHeightHintCache.end());
+            m_minHeightHint = *std::min_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 841e9ca100..fa92b86822 100644
--- a/src/kitemviews/private/kitemlistsizehintresolver.h
+++ b/src/kitemviews/private/kitemlistsizehintresolver.h
@@ -37,6 +37,7 @@ public:
     KItemListSizeHintResolver(const KItemListView* itemListView);
     virtual ~KItemListSizeHintResolver();
     QSizeF maxSizeHint();
+    QSizeF minSizeHint();
     QSizeF sizeHint(int index);
 
     void itemsInserted(const KItemRangeList& itemRanges);
@@ -52,6 +53,7 @@ private:
     mutable QVector<qreal> m_logicalHeightHintCache;
     mutable qreal m_logicalWidthHint;
     mutable qreal m_logicalHeightHint;
+    mutable qreal m_minHeightHint;
     bool m_needsResolving;
 };