[LyX/master] Improve the performance of the source panel by using a QTimer.

[Guillaume Munch]

commit ba3e6cb2d226c670befb93d10a2b65d07aeefd2e
Author: Guillaume Munch <g...@lyx.org>
Date:   Fri Jul 31 01:05:54 2015 +0100

    Improve the performance of the source panel by using a QTimer.
    
    Fix bug #9493. The source panel was very slow with auto-update on. Now
    we use a timer that ensures that the source is generated only at
    rest. The delay is short or long depending on whether we show the
    source of a paragraph or the whole source.

diff --git a/src/frontends/qt4/GuiViewSource.cpp 
b/src/frontends/qt4/GuiViewSource.cpp
index 3fcaed9..50cfa31 100644
--- a/src/frontends/qt4/GuiViewSource.cpp
+++ b/src/frontends/qt4/GuiViewSource.cpp
@@ -46,7 +46,8 @@ namespace frontend {
 ViewSourceWidget::ViewSourceWidget()
        :       bv_(0), document_(new QTextDocument(this)),
                highlighter_(new LaTeXHighlighter(document_)),
-               force_getcontent_(true)
+               force_getcontent_(true),
+               update_timer_(new QTimer(this))
 {
        setupUi(this);
 
@@ -55,14 +56,19 @@ ViewSourceWidget::ViewSourceWidget()
        connect(autoUpdateCB, SIGNAL(toggled(bool)),
                updatePB, SLOT(setDisabled(bool)));
        connect(autoUpdateCB, SIGNAL(toggled(bool)),
-               this, SLOT(updateView()));
+               this, SLOT(updateViewNow()));
        connect(masterPerspectiveCB, SIGNAL(toggled(bool)),
-               this, SLOT(updateView()));
+               this, SLOT(updateViewNow()));
        connect(updatePB, SIGNAL(clicked()),
-               this, SLOT(updateView()));
+               this, SLOT(updateViewNow()));
        connect(outputFormatCO, SIGNAL(activated(int)),
                this, SLOT(setViewFormat()));
 
+       // setting the update timer
+       update_timer_->setSingleShot(true);
+       connect(update_timer_, SIGNAL(timeout()),
+               this, SLOT(realUpdateView()));
+
        // setting a document at this point trigger an assertion in Qt
        // so we disable the signals here:
        document_->blockSignals(true);
@@ -139,7 +145,7 @@ void ViewSourceWidget::setBufferView(BufferView const * bv)
 void ViewSourceWidget::contentsChanged()
 {
        if (autoUpdateCB->isChecked())
-               updateView();
+               updateViewNow();
 }
 
 
@@ -147,12 +153,26 @@ void ViewSourceWidget::setViewFormat()
 {
        view_format_ = outputFormatCO->itemData(
              outputFormatCO->currentIndex()).toString();
-       updateView();
+       updateViewNow();
 }
 
 
 void ViewSourceWidget::updateView()
 {
+       const int long_delay = 400;
+       const int short_delay = 60;
+       // a shorter delay if just the current paragraph is shown
+       update_timer_->start((contentsCO->currentIndex() == 0) ?
+                                               short_delay : long_delay);
+}
+
+void ViewSourceWidget::updateViewNow()
+{
+       update_timer_->start(0);
+}
+
+void ViewSourceWidget::realUpdateView()
+{
        if (!bv_) {
                document_->setPlainText(QString());
                setEnabled(false);
diff --git a/src/frontends/qt4/GuiViewSource.h 
b/src/frontends/qt4/GuiViewSource.h
index c600269..d9425ac 100644
--- a/src/frontends/qt4/GuiViewSource.h
+++ b/src/frontends/qt4/GuiViewSource.h
@@ -20,6 +20,7 @@
 
 #include <QDockWidget>
 #include <QString>
+#include <QTimer>
 
 class QTextDocument;
 
@@ -43,8 +44,10 @@ protected:
        void resizeEvent (QResizeEvent * event);
 
 public Q_SLOTS:
-       /// update content
+       /// schedule an update after delay
        void updateView();
+       /// schedule an update now
+       void updateViewNow();
        ///
        void setViewFormat();
        ///
@@ -52,6 +55,10 @@ public Q_SLOTS:
        ///
        void contentsChanged();
 
+private Q_SLOTS:
+       /// update content
+       void realUpdateView();
+
 private:
        ///
        BufferView const * bv_;
@@ -63,6 +70,8 @@ private:
        bool force_getcontent_;
        ///
        QString view_format_;
+       ///
+       QTimer * update_timer_;
 };