Avoid Text layout being triggered unnecessarily

Text was quite often layed out twice during construction due to
geometry changes, and often at run time due to other geometry changes.
This change checks for cases which do not require relayouting and
drops out early.  These are easier to detect than trying to have a
single giant if statement covering all the positive combinations.

Change-Id: I2deb2ab52d35b3d02bced698d05fef91c9e2f745
Reviewed-by: Michael Brasser <michael.brasser@nokia.com>

1 files changed, 60 insertions, 17 deletions

diff --git a/src/quick/items/qquicktext.cpp b/src/quick/items/qquicktext.cpp
index 274ea93abb..07de537a98 100644
--- a/src/quick/items/qquicktext.cpp
+++ b/src/quick/items/qquicktext.cpp
@@ -224,8 +224,12 @@ void QQuickTextPrivate::updateLayout()
             tmp.replace(QLatin1Char('\n'), QChar::LineSeparator);
             singleline = !tmp.contains(QChar::LineSeparator);
             if (singleline && !maximumLineCountValid && elideMode != QQuickText::ElideNone && q->widthValid() && wrapMode == QQuickText::NoWrap) {
-                QFontMetrics fm(font);
-                tmp = fm.elidedText(tmp,(Qt::TextElideMode)elideMode,q->width());
+                if (q->width() <= 0) {
+                    tmp = QString();
+                } else {
+                    QFontMetrics fm(font);
+                    tmp = fm.elidedText(tmp,(Qt::TextElideMode)elideMode,q->width());
+                }
                 if (tmp != text) {
                     layoutTextElided = true;
                     if (!truncated) {
@@ -536,10 +540,26 @@ QRect QQuickTextPrivate::setupTextLayout()
             layout.setText(elidedText);
     }
 
+    if ((q->widthValid() && q->width() <= 0. && elideMode != QQuickText::ElideNone)
+            || (q->heightValid() && q->height() <= 0. && wrapMode != QQuickText::NoWrap && elideMode == QQuickText::ElideRight)) {
+        // we are elided and we have a zero width or height
+        if (!truncated) {
+            truncated = true;
+            emit q->truncatedChanged();
+        }
+        if (lineCount) {
+            lineCount = 0;
+            emit q->lineCountChanged();
+        }
+
+        qreal height = (lineHeightMode == QQuickText::FixedHeight) ? lineHeight : fm.height() * lineHeight;
+        return QRect(0, 0, 0, height);
+    }
+
     qreal height = 0;
     QRectF br;
 
-    bool truncate = false;
+    bool truncate = layoutTextElided;
     bool customLayout = isLineLaidOutConnected();
     bool elideEnabled = elideMode == QQuickText::ElideRight && q->widthValid();
 
@@ -1633,21 +1653,44 @@ QRectF QQuickText::boundingRect() const
 void QQuickText::geometryChanged(const QRectF &newGeometry, const QRectF &oldGeometry)
 {
     Q_D(QQuickText);
-    bool elide = d->elideMode != QQuickText::ElideNone && widthValid();
-    if ((!d->internalWidthUpdate
-         && (newGeometry.width() != oldGeometry.width() || (elide && newGeometry.height() != oldGeometry.height())))
-            && (d->wrapMode != QQuickText::NoWrap
-                || d->elideMode != QQuickText::ElideNone
-                || d->hAlign != QQuickText::AlignLeft)) {
-        if ((d->singleline || d->maximumLineCountValid || heightValid()) && elide) {
-            // We need to re-elide
-            d->updateLayout();
-        } else {
-            // We just need to re-layout
-            d->updateSize();
-        }
+    bool widthChanged = newGeometry.width() != oldGeometry.width();
+    bool heightChanged = newGeometry.height() != oldGeometry.height();
+    bool leftAligned = effectiveHAlign() == QQuickText::AlignLeft;
+    bool wrapped = d->wrapMode != QQuickText::NoWrap;
+    bool elide = d->elideMode != QQuickText::ElideNone;
+
+    if ((!widthChanged && !heightChanged) || d->internalWidthUpdate)
+        goto geomChangeDone;
+
+    if (leftAligned && !wrapped && !elide)
+        goto geomChangeDone; // left aligned unwrapped text without eliding never needs relayout
+
+    if (!widthChanged && !wrapped && d->singleline)
+        goto geomChangeDone; // only height has changed which doesn't affect single line unwrapped text
+
+    if (!widthChanged && wrapped && d->elideMode != QQuickText::ElideRight)
+        goto geomChangeDone; // only height changed and no multiline eliding.
+
+    if (leftAligned && d->elideMode == QQuickText::ElideRight && !d->truncated && d->singleline
+            && !wrapped && newGeometry.width() > oldGeometry.width())
+        goto geomChangeDone; // Eliding not affected if we're not currently truncated and we get wider.
+
+    if (d->elideMode == QQuickText::ElideRight && wrapped && newGeometry.height() > oldGeometry.height()) {
+        if (!d->truncated)
+            goto geomChangeDone; // Multiline eliding not affected if we're not currently truncated and we get higher.
+        if (d->maximumLineCountValid && d->lineCount == d->maximumLineCount)
+            goto geomChangeDone; // Multiline eliding not affected if we're already at max line count and we get higher.
     }
 
+    if (d->updateOnComponentComplete || (elide && widthValid())) {
+        // We need to re-elide
+        d->updateLayout();
+    } else {
+        // We just need to re-layout
+        d->updateSize();
+    }
+
+geomChangeDone:
     QQuickItem::geometryChanged(newGeometry, oldGeometry);
 }
 
@@ -1724,7 +1767,7 @@ QSGNode *QQuickText::updatePaintNode(QSGNode *oldNode, UpdatePaintNodeData *data
             d->ensureDoc();
             node->addTextDocument(bounds.topLeft(), d->doc, d->color, d->style, d->styleColor);
 
-        } else {
+        } else if (d->elideMode == QQuickText::ElideNone || bounds.width() > 0.) {
             node->addTextLayout(QPoint(0, bounds.y()), &d->layout, d->color, d->style, d->styleColor);
             if (d->elipsisLayout)
                 node->addTextLayout(QPoint(0, bounds.y()), d->elipsisLayout, d->color, d->style, d->styleColor);