Do not let QML warnings reduce the frame rate in fullscreen mode.

QPlainTextEdit::appendPlainText() can take surprisingly long, even
when the widget is hidden. In a demo on embedded hardware we've seen
the frame time go up from ~55 milliseconds to ~85 over the first few
minutes of the demo running. There was one warning emitted per frame.
With this patch there is no significant performance degradation.

Change-Id: Ic80409b29a1544f03431e1573811a00925660338
Reviewed-by: Matthew Vogt <matthew.vogt@nokia.com>

2 files changed, 9 insertions, 0 deletions

diff --git a/tools/qml/loggerwidget.cpp b/tools/qml/loggerwidget.cpp
index 3456d96c..7db3fc83 100644
--- a/tools/qml/loggerwidget.cpp
+++ b/tools/qml/loggerwidget.cpp
@@ -104,6 +104,11 @@ LoggerWidget::LoggerWidget(QWidget *parent) :
 
 void LoggerWidget::append(const QString &msg)
 {
+    if (!isVisible()) {
+        // appending the message for real can take a couple of milliseconds, so if we don't have to...
+        m_queuedMessages.append(msg);
+        return;
+    }
     m_plainTextEdit->appendPlainText(msg);
 
     if (!isVisible() && (defaultVisibility() == AutoShowWarnings))
@@ -174,6 +179,9 @@ void LoggerWidget::warningsPreferenceChanged(QAction *action)
 
 void LoggerWidget::showEvent(QShowEvent *event)
 {
+    foreach (const QString &msg, m_queuedMessages)
+        m_plainTextEdit->appendPlainText(msg);
+    m_queuedMessages.clear();
     QWidget::showEvent(event);
     emit opened();
 }
diff --git a/tools/qml/loggerwidget.h b/tools/qml/loggerwidget.h
index 8ec25f02..bc9991cb 100644
--- a/tools/qml/loggerwidget.h
+++ b/tools/qml/loggerwidget.h
@@ -92,6 +92,7 @@ private:
     enum ConfigOrigin { CommandLineOrigin, SettingsOrigin };
     ConfigOrigin m_visibilityOrigin;
     Visibility m_visibility;
+    QStringList m_queuedMessages;
 };
 
 QT_END_NAMESPACE