QTextDocument/QGraphicsTextItem: skip layout in setTextWidth(0)

In a QGraphicsTextItem without a width yet, there's no need to do any
layouting. The use case is obviously items with an app-defined size,
not the default where text items adapt to their contents.

Results:
 0.065 msecs to create a QGraphicsTextItem with some text (layouted)
 0.036 msecs to set everything up in a QGraphicsTextItem with 0 width

QTextEdit was abusing the width 0 to mean "no wrap, width comes from
contents", but since the value -1 means that already in QTextDocument,
QTextEdit now uses a width of -1 for that meaning.

Change-Id: I67ad59c305e5dd34830886e4e6c56dde03c93668
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>
Reviewed-by: Volker Hilsheimer <volker.hilsheimer@qt.io>

2 files changed, 22 insertions, 2 deletions

diff --git a/tests/auto/widgets/widgets/qtextedit/tst_qtextedit.cpp b/tests/auto/widgets/widgets/qtextedit/tst_qtextedit.cpp
index bc533df48a..72d2cc7aa7 100644
--- a/tests/auto/widgets/widgets/qtextedit/tst_qtextedit.cpp
+++ b/tests/auto/widgets/widgets/qtextedit/tst_qtextedit.cpp
@@ -1194,8 +1194,9 @@ void tst_QTextEdit::undoRedoShouldRepositionTextEditCursor()
 void tst_QTextEdit::lineWrapModes()
 {
     ed->setLineWrapMode(QTextEdit::NoWrap);
-    // NoWrap at the same time as having all lines that are all left aligned means we optimize to only layout once. The effect is that the width is always 0
-    QCOMPARE(ed->document()->pageSize().width(), qreal(0));
+    // NoWrap at the same time as having all lines that are all left aligned means we optimize to
+    // only layout once. The effect is that the width is always -1
+    QCOMPARE(ed->document()->pageSize().width(), qreal(-1));
 
     QTextCursor cursor = QTextCursor(ed->document());
     cursor.insertText(QString("A simple line"));
diff --git a/tests/benchmarks/widgets/graphicsview/qgraphicsitem/tst_qgraphicsitem.cpp b/tests/benchmarks/widgets/graphicsview/qgraphicsitem/tst_qgraphicsitem.cpp
index fd74a7b3b9..536d366b63 100644
--- a/tests/benchmarks/widgets/graphicsview/qgraphicsitem/tst_qgraphicsitem.cpp
+++ b/tests/benchmarks/widgets/graphicsview/qgraphicsitem/tst_qgraphicsitem.cpp
@@ -5,6 +5,7 @@
 #include <QGraphicsItem>
 #include <QGraphicsScene>
 #include <QGraphicsView>
+#include <QTextDocument>
 
 class tst_QGraphicsItem : public QObject
 {
@@ -33,6 +34,7 @@ private slots:
     void shear();
     void translate();
     void createTextItem();
+    void createTextItemZeroWidth();
 };
 
 tst_QGraphicsItem::tst_QGraphicsItem()
@@ -216,5 +218,22 @@ void tst_QGraphicsItem::createTextItem()
     }
 }
 
+void tst_QGraphicsItem::createTextItemZeroWidth()
+{
+    // Ensure QFontDatabase loaded the font beforehand
+    QFontInfo(qApp->font()).family();
+    const QString text = "This is some text";
+    QBENCHMARK {
+        QGraphicsTextItem item;
+        item.document()->setTextWidth(0);
+        // Prepare everything
+        item.setPlainText(text);
+        QTextOption option = item.document()->defaultTextOption();
+        option.setAlignment(Qt::AlignHCenter);
+        item.document()->setDefaultTextOption(option);
+        // And (in a real app) set actual text width here
+    }
+}
+
 QTEST_MAIN(tst_QGraphicsItem)
 #include "tst_qgraphicsitem.moc"