Fix #3926: QCursor in AFP

Fix a crash that occurred on the following steps:
1. Add an AFP track.
2. Open it, and move the waveform display to overlap the track label
button.
3. Close the AFP window and open it again by clicking the track label.
4. Move the mouse pointer.

The problem occurs because the code makes the implicit assumption that
AudioFileProcessorWaveView::enterEvent (and hence
QApplication::setOverrideCursor) is called before
AudioFileProcessorWaveView::mouseMoveEvent. This is not the case when
the waveform display is on top of the track label. In this case the AFP
windows is opened with the mouse being immediately positioned over the
wave form display. There is no enter event and move events are issues
directly. This then leads to a crash in
AudioFileProcessorWaveView::mouseMoveEvent when trying to determine the
value for is_size_cursor because the override cursor is still null but
is dereferenced directly without checking.

Only adding a check would not solve the problem because in that case the
cursor would not change to the hand cursor when being moved inside the
waveform display.

The solution is to remove all calls to the global methods
setOverrideCursor and restoreOverrideCursor and to only set the cursor
locally.

This fix is based on a patch by gi0e5b06 which is committed under 8a10c52
in his repository but for which he never created a pull request.

plugins/audio_file_processor/audio_file_processor.cpp

@@ -795,6 +795,7 @@ AudioFileProcessorWaveView::AudioFileProcessorWaveView( QWidget * _parent, int _
 
 	m_graph.fill( Qt::transparent );
 	update();
+	updateCursor();
 }
 
 
@@ -811,18 +812,15 @@ void AudioFileProcessorWaveView::isPlaying( f_cnt_t _current_frame )
 
 void AudioFileProcessorWaveView::enterEvent( QEvent * _e )
 {
-	QApplication::setOverrideCursor( Qt::OpenHandCursor );
+	updateCursor();
 }
 
 
 
 
 void AudioFileProcessorWaveView::leaveEvent( QEvent * _e )
 {
-	while( QApplication::overrideCursor() )
-	{
-		QApplication::restoreOverrideCursor();
-	}
+	updateCursor();
 }
 
 
@@ -850,7 +848,7 @@ void AudioFileProcessorWaveView::mousePressEvent( QMouseEvent * _me )
 	else
 	{
 		m_draggingType = wave;
-		QApplication::setOverrideCursor( Qt::ClosedHandCursor );
+		updateCursor(_me);
 	}
 }
 
@@ -862,7 +860,7 @@ void AudioFileProcessorWaveView::mouseReleaseEvent( QMouseEvent * _me )
 	m_isDragging = false;
 	if( m_draggingType == wave )
 	{
-		QApplication::restoreOverrideCursor();
+		updateCursor(_me);
 	}
 }
 
@@ -873,22 +871,7 @@ void AudioFileProcessorWaveView::mouseMoveEvent( QMouseEvent * _me )
 {
 	if( ! m_isDragging )
 	{
-		const bool is_size_cursor =
-			QApplication::overrideCursor()->shape() == Qt::SizeHorCursor;
-
-		if( isCloseTo( _me->x(), m_startFrameX ) ||
-			isCloseTo( _me->x(), m_endFrameX ) ||
-			isCloseTo( _me->x(), m_loopFrameX ) )
-		{
-			if( ! is_size_cursor )
-			{
-				QApplication::setOverrideCursor( Qt::SizeHorCursor );
-			}
-		}
-		else if( is_size_cursor )
-		{
-			QApplication::restoreOverrideCursor();
-		}
+		updateCursor(_me);
 		return;
 	}
 
@@ -1261,6 +1244,24 @@ void AudioFileProcessorWaveView::reverse()
 
 
 
+void AudioFileProcessorWaveView::updateCursor( QMouseEvent * _me )
+{
+	bool const waveIsDragged = m_isDragging && (m_draggingType == wave);
+	bool const pointerCloseToStartEndOrLoop = (_me != nullptr ) &&
+			( isCloseTo( _me->x(), m_startFrameX ) ||
+			  isCloseTo( _me->x(), m_endFrameX ) ||
+			  isCloseTo( _me->x(), m_loopFrameX ) );
+
+	if( !m_isDragging && pointerCloseToStartEndOrLoop)
+		setCursor(Qt::SizeHorCursor);
+	else if( waveIsDragged )
+		setCursor(Qt::ClosedHandCursor);
+	else
+		setCursor(Qt::OpenHandCursor);
+}
+
+
+
 
 void AudioFileProcessorWaveView::knob::slideTo( double _v, bool _check_bound )
 {

plugins/audio_file_processor/audio_file_processor.h

@@ -211,7 +211,6 @@ class AudioFileProcessorWaveView : public QWidget
 
 	private:
 		bool checkBound( double _v ) const;
-
 	} ;
 
 
@@ -276,6 +275,7 @@ public slots:
 
 	void updateGraph();
 	void reverse();
+	void updateCursor( QMouseEvent * _me = nullptr );
 
 	static bool isCloseTo( int _a, int _b )
 	{