Make the handling of the "maximum text lines" setting more robust

If the user sets a maximum number of text lines in the settings, this
number was translated into a maximum height in pixels using
QFontMetrics::lineSpacing() before this commit.

In KStandardItemListWidgetInformant::itemSizeHint(), this maximum height
limited the size that is reserved for the item.

However, in KStandardItemListWidget::updateIconsLayoutTextCache(), the
maximum height was translated back into a maximum number of lines,
which limits the number of lines that are created using the QTextLayout.

This approach could lead to problems if the real height of the layouted
text is 1 pixel more or less than QFontMetrics::lineSpacing() times
"number of lines".

Now we do not store a "maximum height" inside the "maximum size"
explicitly, but store a maximum number of lines and a maximum with (for
Compact View) separately, and then use the number of lines also to
calculate the required size in
KStandardItemListWidgetInformant::itemSizeHint(). This should make sure
that the correct height is reserved for each item.

Thanks to Christoph Feck and Emmanuel Pescosta for helping to debug this
problem and testing the patch.

BUG: 323841
FIXED-IN: 4.13
REVIEW: 113871

4 files changed, 17 insertions, 14 deletions

diff --git a/src/kitemviews/kitemliststyleoption.cpp b/src/kitemviews/kitemliststyleoption.cpp
index ac2587962..edd6363c8 100644
--- a/src/kitemviews/kitemliststyleoption.cpp
+++ b/src/kitemviews/kitemliststyleoption.cpp
@@ -31,7 +31,8 @@ KItemListStyleOption::KItemListStyleOption() :
     verticalMargin(-1),
     iconSize(-1),
     extendedSelectionRegion(false),
-    maxTextSize()
+    maxTextLines(0),
+    maxTextWidth(0)
 {
 }
 
@@ -45,7 +46,8 @@ KItemListStyleOption::KItemListStyleOption(const KItemListStyleOption& other) :
     verticalMargin(other.verticalMargin),
     iconSize(other.iconSize),
     extendedSelectionRegion(other.extendedSelectionRegion),
-    maxTextSize(other.maxTextSize)
+    maxTextLines(other.maxTextLines),
+    maxTextWidth(other.maxTextWidth)
 {
 }
 
diff --git a/src/kitemviews/kitemliststyleoption.h b/src/kitemviews/kitemliststyleoption.h
index 1a304fc28..782dd0ec2 100644
--- a/src/kitemviews/kitemliststyleoption.h
+++ b/src/kitemviews/kitemliststyleoption.h
@@ -43,7 +43,8 @@ public:
     int verticalMargin;
     int iconSize;
     bool extendedSelectionRegion;
-    QSize maxTextSize;
+    int maxTextLines;
+    int maxTextWidth;
 };
 #endif
 
diff --git a/src/kitemviews/kitemlistview.cpp b/src/kitemviews/kitemlistview.cpp
index ab420cab1..f1b35fa53 100644
--- a/src/kitemviews/kitemlistview.cpp
+++ b/src/kitemviews/kitemlistview.cpp
@@ -760,7 +760,8 @@ void KItemListView::setStyleOption(const KItemListStyleOption& option)
         updateGroupHeaderHeight();
     }
 
-    if (animate && previousOption.maxTextSize != option.maxTextSize) {
+    if (animate &&
+        (previousOption.maxTextLines != option.maxTextLines || previousOption.maxTextWidth != option.maxTextWidth)) {
         // Animating a change of the maximum text size just results in expensive
         // temporary eliding and clipping operations and does not look good visually.
         animate = false;
diff --git a/src/kitemviews/kstandarditemlistwidget.cpp b/src/kitemviews/kstandarditemlistwidget.cpp
index 9a9a734ed..9f7b26959 100644
--- a/src/kitemviews/kstandarditemlistwidget.cpp
+++ b/src/kitemviews/kstandarditemlistwidget.cpp
@@ -130,7 +130,6 @@ void KStandardItemListWidgetInformant::calculateIconsLayoutItemSizeHints(QVector
 
     const qreal itemWidth = view->itemSize().width();
     const qreal maxWidth = itemWidth - 2 * option.padding;
-    const qreal maxTextHeight = option.maxTextSize.height();
     const qreal additionalRolesSpacing = additionalRolesCount * option.fontMetrics.lineSpacing();
     const qreal spacingAndIconHeight = option.iconSize + option.padding * 3;
 
@@ -150,20 +149,22 @@ void KStandardItemListWidgetInformant::calculateIconsLayoutItemSizeHints(QVector
         layout.setTextOption(textOption);
         layout.beginLayout();
         QTextLine line;
+        int lineCount = 0;
         while ((line = layout.createLine()).isValid()) {
             line.setLineWidth(maxWidth);
             line.naturalTextWidth();
             textHeight += line.height();
+
+            ++lineCount;
+            if (lineCount == option.maxTextLines) {
+                break;
+            }
         }
         layout.endLayout();
 
         // Add one line for each additional information
         textHeight += additionalRolesSpacing;
 
-        if (maxTextHeight > 0 && textHeight > maxTextHeight) {
-            textHeight = maxTextHeight;
-        }
-
         sizeHints[index] = QSizeF(itemWidth, textHeight + spacingAndIconHeight);
     }
 }
@@ -176,7 +177,7 @@ void KStandardItemListWidgetInformant::calculateCompactLayoutItemSizeHints(QVect
 
     const QList<QByteArray>& visibleRoles = view->visibleRoles();
     const bool showOnlyTextRole = (visibleRoles.count() == 1) && (visibleRoles.first() == "text");
-    const qreal maxWidth = option.maxTextSize.width();
+    const qreal maxWidth = option.maxTextWidth;
     const qreal paddingAndIconWidth = option.padding * 4 + option.iconSize;
     const qreal height = option.padding * 2 + qMax(option.iconSize, (1 + additionalRolesCount) * option.fontMetrics.lineSpacing());
 
@@ -1066,9 +1067,6 @@ void KStandardItemListWidget::updateIconsLayoutTextCache()
     qreal nameHeight = 0;
     QTextLine line;
 
-    const int additionalRolesCount = qMax(visibleRoles().count() - 1, 0);
-    const int maxNameLines = (option.maxTextSize.height() / int(lineSpacing)) - additionalRolesCount;
-
     QTextLayout layout(nameTextInfo->staticText.text(), m_customizedFont);
     layout.setTextOption(nameTextInfo->staticText.textOption());
     layout.beginLayout();
@@ -1079,7 +1077,7 @@ void KStandardItemListWidget::updateIconsLayoutTextCache()
         nameHeight += line.height();
 
         ++nameLineIndex;
-        if (nameLineIndex == maxNameLines) {
+        if (nameLineIndex == option.maxTextLines) {
             // The maximum number of textlines has been reached. If this is
             // the case provide an elided text if necessary.
             const int textLength = line.textStart() + line.textLength();
@@ -1101,6 +1099,7 @@ void KStandardItemListWidget::updateIconsLayoutTextCache()
     layout.endLayout();
 
     // Use one line for each additional information
+    const int additionalRolesCount = qMax(visibleRoles().count() - 1, 0);
     nameTextInfo->staticText.setTextWidth(maxWidth);
     nameTextInfo->pos = QPointF(padding, widgetHeight -
                                          nameHeight -