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>

src/gui/text/qtextdocument_p.h

@@ -291,6 +291,11 @@ public:
         return get(object->document());
     }
 
+    // Only test the width for 0:
+    // * setTextWidth(x) leads to height -1, which is valid
+    // * the default page size of (-1, -1) means size determined from contents, this is valid too
+    bool canLayout() const { return !qIsNull(pageSize.width()); }
+
 private:
     QTextDocumentPrivate(const QTextDocumentPrivate& m);
     QTextDocumentPrivate& operator= (const QTextDocumentPrivate& m);

src/gui/text/qtextdocumentlayout.cpp

@@ -3705,7 +3705,7 @@ void QTextDocumentLayout::draw(QPainter *painter, const PaintContext &context)
     }
 
     QFixed width = fd->size.width;
-    if (d->document->pageSize().width() == 0 && d->viewportRect.isValid()) {
+    if (d->document->pageSize().width() == -1 && d->viewportRect.isValid()) {
         // we're in NoWrap mode, meaning the frame should expand to the viewport
         // so that backgrounds are drawn correctly
         fd->size.width = qMax(width, QFixed::fromReal(d->viewportRect.right()));
@@ -3754,7 +3754,7 @@ void QTextDocumentLayout::documentChanged(int from, int oldLength, int length)
      for (; blockIt.isValid() && blockIt != endIt; blockIt = blockIt.next())
          blockIt.clearLayout();
 
-    if (d->docPrivate->pageSize.isNull())
+    if (!d->docPrivate->canLayout())
         return;
 
     QRectF updateRect;
@@ -4032,7 +4032,7 @@ QRectF QTextDocumentLayout::tableCellBoundingRect(QTextTable *table, const QText
 QRectF QTextDocumentLayout::tableBoundingRect(QTextTable *table) const
 {
     Q_D(const QTextDocumentLayout);
-    if (d->docPrivate->pageSize.isNull())
+    if (!d->docPrivate->canLayout())
         return QRectF();
     d->ensureLayoutFinished();
 
@@ -4059,7 +4059,7 @@ QRectF QTextDocumentLayout::tableBoundingRect(QTextTable *table) const
 QRectF QTextDocumentLayout::frameBoundingRect(QTextFrame *frame) const
 {
     Q_D(const QTextDocumentLayout);
-    if (d->docPrivate->pageSize.isNull())
+    if (!d->docPrivate->canLayout())
         return QRectF();
     d->ensureLayoutFinished();
     return d->frameBoundingRectInternal(frame);
@@ -4088,7 +4088,7 @@ QRectF QTextDocumentLayoutPrivate::frameBoundingRectInternal(QTextFrame *frame)
 QRectF QTextDocumentLayout::blockBoundingRect(const QTextBlock &block) const
 {
     Q_D(const QTextDocumentLayout);
-    if (d->docPrivate->pageSize.isNull() || !block.isValid() || !block.isVisible())
+    if (!d->docPrivate->canLayout() || !block.isValid() || !block.isVisible())
         return QRectF();
     d->ensureLayoutedByPosition(block.position() + block.length());
     QTextFrame *frame = d->document->frameAt(block.position());

src/widgets/widgets/qtextedit.cpp

@@ -1521,7 +1521,7 @@ void QTextEditPrivate::relayoutDocument()
         QVariant alignmentProperty = doc->documentLayout()->property("contentHasAlignment");
         if (alignmentProperty.userType() == QMetaType::Bool && !alignmentProperty.toBool()) {
 
-            width = 0;
+            width = -1;
         }
     }
 

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"));

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"