Add repaint optimization to TQProgressBar

This optimization makes TQProgressBar::setProgress() only repaint itself
if stepping to the new progress would cause a graphical change. This means
that for a width W and a total number of steps S, it will repaint itself
'W' times (every 'S/W' steps) instead of 'S' times (every step) as it is
right now.
(cherry picked from commit 9f882f9de7)

src/widgets/qprogressbar.cpp

@@ -50,6 +50,14 @@
 #endif
 #include <limits.h>
 
+class QProgressBarPrivate
+{
+    public:
+        QProgressBarPrivate() : last_painted_progress( 0 ) { }
+
+    int last_painted_progress;
+};
+
 /*!
     \class QProgressBar qprogressbar.h
     \brief The QProgressBar widget provides a horizontal progress bar.
@@ -102,7 +110,7 @@ QProgressBar::QProgressBar( QWidget *parent, const char *name, WFlags f )
       center_indicator( TRUE ),
       auto_indicator( TRUE ),
       percentage_visible( TRUE ),
-      d( 0 )
+      d( new QProgressBarPrivate )
 {
     setSizePolicy( QSizePolicy( QSizePolicy::Expanding, QSizePolicy::Fixed ) );
     initFrame();
@@ -133,13 +141,23 @@ QProgressBar::QProgressBar( int totalSteps,
       center_indicator( TRUE ),
       auto_indicator( TRUE ),
       percentage_visible( TRUE ),
-      d( 0 )
+      d( new QProgressBarPrivate )
 {
     setSizePolicy( QSizePolicy( QSizePolicy::Expanding, QSizePolicy::Fixed ) );
     initFrame();
 }
 
 
+/*!
+    Destroys the object and frees any allocated ressources.
+*/
+ 
+QProgressBar::~QProgressBar()
+{
+    delete d;
+}
+
+
 /*!
     Reset the progress bar. The progress bar "rewinds" and shows no
     progress.
@@ -191,11 +209,16 @@ void QProgressBar::setProgress( int progress )
 	 progress < 0 || ( ( progress > total_steps ) && total_steps ) )
 	return;
 
+    const bool needRepaint = isVisible() && requireRepaint( progress );
+
     progress_val = progress;
 
     setIndicator( progress_str, progress_val, total_steps );
 
-    repaint( FALSE );
+    if ( needRepaint ) {
+        repaint( FALSE );
+        d->last_painted_progress = progress;
+    }
 
 #if defined(QT_ACCESSIBILITY_SUPPORT)
     QAccessible::updateAccessibility( this, 0, QAccessible::ValueChanged );
@@ -321,6 +344,32 @@ void QProgressBar::styleChange( QStyle& old )
     QFrame::styleChange( old );
 }
 
+/*!
+    This method returns whether changing the progress to the \a newValue
+    would require a repaint of the progress bar. This allows efficient
+    repainting.
+*/
+bool QProgressBar::requireRepaint( int newProgress ) const
+{
+    if ( newProgress == progress_val ||
+         newProgress == d->last_painted_progress ) {
+        return false;
+    }
+
+    const int width = contentsRect().width();
+    if ( width == 0 ) {
+        return false;
+    }
+
+    float progressPerPixel = 1.0;
+    if ( total_steps > width ) {
+        progressPerPixel = float( total_steps ) / float( width );
+    }
+
+    const int delta = d->last_painted_progress - newProgress;
+    return QABS( delta ) >= progressPerPixel;
+}
+
 
 /*!
     This method is called to generate the text displayed in the center

src/widgets/qprogressbar.h

@@ -64,6 +64,7 @@ class Q_EXPORT QProgressBar : public QFrame
 public:
     QProgressBar( QWidget* parent=0, const char* name=0, WFlags f=0 );
     QProgressBar( int totalSteps, QWidget* parent=0, const char* name=0, WFlags f=0 );
+    virtual ~QProgressBar();
 
     int		totalSteps() const;
     int		progress()   const;
@@ -94,6 +95,7 @@ protected:
     virtual bool setIndicator( QString & progress_str, int progress,
 			       int totalSteps );
     void styleChange( QStyle& );
+    bool	requireRepaint( int newProgress ) const;
 
 private:
     int		total_steps;