[PATCH] Improve the performance of the source panel by using a QTimer (bug #9493)

[Guillaume Munch]

Improve the performance of the source panel by using a QTimer. Solves 
<http://www.lyx.org/trac/ticket/9493>. Please criticise.
>From d25446e1dc4aa62eae239fa95098134a1c71d9c0 Mon Sep 17 00:00:00 2001
From: gadmm <ga...@free.fr>
Date: Fri, 31 Jul 2015 01:05:54 +0100
Subject: [PATCH] Improve the performance of the source panel by using a
 QTimer.
---
 src/frontends/qt4/GuiViewSource.cpp | 32 ++++++++++++++++++++++++++------
 src/frontends/qt4/GuiViewSource.h   | 11 ++++++++++-
 2 files changed, 36 insertions(+), 7 deletions(-)

diff --git a/src/frontends/qt4/GuiViewSource.cpp b/src/frontends/qt4/GuiViewSource.cpp
index 3fcaed9..ede7e3e 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 = 40;
+	// 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_;
 };
 
 
-- 
2.1.4