Separate width and height info in the layouting code

By separating the width and height info, we can save some unnecessary
overhead in terms of memory and CPU cycles, and make the calculation of
the height of a row (or the width of a column in Compact View) a bit
simpler.

To achieve this, this patch extends the concept of "logical rows"
(which are actually columns in Compact View) to "logical width" and
"logical height" (which is the actual height and width, respectively, in
 Compact View). The distinction between rows/columns and "logical"
rows/columns may be a bit confusing, but the confusion is already in the
current code, and I hope that it will be mitigated a bit by prefixing
the corresponding variables with "logical".

REVIEW: 118454

1 files changed, 23 insertions, 22 deletions

diff --git a/src/kitemviews/private/kitemlistsizehintresolver.cpp b/src/kitemviews/private/kitemlistsizehintresolver.cpp
index 029beddf9..1d8067026 100644
--- a/src/kitemviews/private/kitemlistsizehintresolver.cpp
+++ b/src/kitemviews/private/kitemlistsizehintresolver.cpp
@@ -23,7 +23,8 @@
 
 KItemListSizeHintResolver::KItemListSizeHintResolver(const KItemListView* itemListView) :
     m_itemListView(itemListView),
-    m_sizeHintCache(),
+    m_logicalHeightHintCache(),
+    m_logicalWidthHint(0.0),
     m_needsResolving(false)
 {
 }
@@ -35,7 +36,7 @@ KItemListSizeHintResolver::~KItemListSizeHintResolver()
 QSizeF KItemListSizeHintResolver::sizeHint(int index)
 {
     updateCache();
-    return m_sizeHintCache.at(index);
+    return QSizeF(m_logicalWidthHint, m_logicalHeightHintCache.at(index));
 }
 
 void KItemListSizeHintResolver::itemsInserted(const KItemRangeList& itemRanges)
@@ -45,15 +46,15 @@ void KItemListSizeHintResolver::itemsInserted(const KItemRangeList& itemRanges)
         insertedCount += range.count;
     }
 
-    const int currentCount = m_sizeHintCache.count();
-    m_sizeHintCache.reserve(currentCount + insertedCount);
+    const int currentCount = m_logicalHeightHintCache.count();
+    m_logicalHeightHintCache.reserve(currentCount + insertedCount);
 
     // We build the new list from the end to the beginning to mimize the
     // number of moves.
-    m_sizeHintCache.insert(m_sizeHintCache.end(), insertedCount, QSizeF());
+    m_logicalHeightHintCache.insert(m_logicalHeightHintCache.end(), insertedCount, 0.0);
 
     int sourceIndex = currentCount - 1;
-    int targetIndex = m_sizeHintCache.count() - 1;
+    int targetIndex = m_logicalHeightHintCache.count() - 1;
     int itemsToInsertBeforeCurrentRange = insertedCount;
 
     for (int rangeIndex = itemRanges.count() - 1; rangeIndex >= 0; --rangeIndex) {
@@ -62,33 +63,33 @@ void KItemListSizeHintResolver::itemsInserted(const KItemRangeList& itemRanges)
 
         // First: move all existing items that must be put behind 'range'.
         while (targetIndex >= itemsToInsertBeforeCurrentRange + range.index + range.count) {
-            m_sizeHintCache[targetIndex] = m_sizeHintCache[sourceIndex];
+            m_logicalHeightHintCache[targetIndex] = m_logicalHeightHintCache[sourceIndex];
             --sourceIndex;
             --targetIndex;
         }
 
         // Then: insert QSizeF() for the items which are inserted into 'range'.
         while (targetIndex >= itemsToInsertBeforeCurrentRange + range.index) {
-            m_sizeHintCache[targetIndex] = QSizeF();
+            m_logicalHeightHintCache[targetIndex] = 0.0;
             --targetIndex;
         }
     }
 
     m_needsResolving = true;
 
-    Q_ASSERT(m_sizeHintCache.count() == m_itemListView->model()->count());
+    Q_ASSERT(m_logicalHeightHintCache.count() == m_itemListView->model()->count());
 }
 
 void KItemListSizeHintResolver::itemsRemoved(const KItemRangeList& itemRanges)
 {
-    const QVector<QSizeF>::iterator begin = m_sizeHintCache.begin();
-    const QVector<QSizeF>::iterator end = m_sizeHintCache.end();
+    const QVector<qreal>::iterator begin = m_logicalHeightHintCache.begin();
+    const QVector<qreal>::iterator end = m_logicalHeightHintCache.end();
 
     KItemRangeList::const_iterator rangeIt = itemRanges.constBegin();
     const KItemRangeList::const_iterator rangeEnd = itemRanges.constEnd();
 
-    QVector<QSizeF>::iterator destIt = begin + rangeIt->index;
-    QVector<QSizeF>::iterator srcIt = destIt + rangeIt->count;
+    QVector<qreal>::iterator destIt = begin + rangeIt->index;
+    QVector<qreal>::iterator srcIt = destIt + rangeIt->count;
 
     ++rangeIt;
 
@@ -104,33 +105,33 @@ void KItemListSizeHintResolver::itemsRemoved(const KItemRangeList& itemRanges)
         }
     }
 
-    m_sizeHintCache.erase(destIt, end);
+    m_logicalHeightHintCache.erase(destIt, end);
 
     // Note that the cache size might temporarily not match the model size if
     // this function is called from KItemListView::setModel() to empty the cache.
-    if (!m_sizeHintCache.isEmpty() && m_itemListView->model()) {
-        Q_ASSERT(m_sizeHintCache.count() == m_itemListView->model()->count());
+    if (!m_logicalHeightHintCache.isEmpty() && m_itemListView->model()) {
+        Q_ASSERT(m_logicalHeightHintCache.count() == m_itemListView->model()->count());
     }
 }
 
 void KItemListSizeHintResolver::itemsMoved(const KItemRange& range, const QList<int>& movedToIndexes)
 {
-    QVector<QSizeF> newSizeHintCache(m_sizeHintCache);
+    QVector<qreal> newLogicalHeightHintCache(m_logicalHeightHintCache);
 
     const int movedRangeEnd = range.index + range.count;
     for (int i = range.index; i < movedRangeEnd; ++i) {
         const int newIndex = movedToIndexes.at(i - range.index);
-        newSizeHintCache[newIndex] = m_sizeHintCache.at(i);
+        newLogicalHeightHintCache[newIndex] = m_logicalHeightHintCache.at(i);
     }
 
-    m_sizeHintCache = newSizeHintCache;
+    m_logicalHeightHintCache = newLogicalHeightHintCache;
 }
 
 void KItemListSizeHintResolver::itemsChanged(int index, int count, const QSet<QByteArray>& roles)
 {
     Q_UNUSED(roles);
     while (count) {
-        m_sizeHintCache[index] = QSizeF();
+        m_logicalHeightHintCache[index] = 0.0;
         ++index;
         --count;
     }
@@ -140,14 +141,14 @@ void KItemListSizeHintResolver::itemsChanged(int index, int count, const QSet<QB
 
 void KItemListSizeHintResolver::clearCache()
 {
-    m_sizeHintCache.fill(QSizeF());
+    m_logicalHeightHintCache.fill(0.0);
     m_needsResolving = true;
 }
 
 void KItemListSizeHintResolver::updateCache()
 {
     if (m_needsResolving) {
-        m_itemListView->calculateItemSizeHints(m_sizeHintCache);
+        m_itemListView->calculateItemSizeHints(m_logicalHeightHintCache, m_logicalWidthHint);
         m_needsResolving = false;
     }
 }