timeline

[franco.amato]

Hi to all, I'm developing an audio editor that at the moment has basic functionalities as draw the sound waveform, play the sound.
I would implement a time line ( a moving vertical line ) that give to the user an idea of which part of the sound is playing.
In the paintEvent I have to draw the waveform ( cached in a QImage ) and the time line.

This is my paintEvent

void WaveWidget::paintEvent( QPaintEvent* pe )
{
	// Update the ev->rect area with the wave from the rendered QPixmap here
 
	if( m_waveCachePixmap.isNull() )
	{
		updateWave();
	}
 
	QPainter p( this );
	QPen pen = QPen(Qt::blue, 1);
	p.setRenderHint( QPainter::Antialiasing, true );
	p.drawImage( 0, 0, m_waveCachePixmap );
 
	QRect& rect = QRect(pe->rect());
	p.setPen(pen);
 
	p.drawLine( rect.x(), 0, rect.x(), height()  );
}

void WaveWidget::paintEvent( QPaintEvent* pe )
{
	// Update the ev->rect area with the wave from the rendered QPixmap here

	if( m_waveCachePixmap.isNull() )
	{
		updateWave();
	}

	QPainter p( this );
	QPen pen = QPen(Qt::blue, 1);
	p.setRenderHint( QPainter::Antialiasing, true );
	p.drawImage( 0, 0, m_waveCachePixmap );

	QRect& rect = QRect(pe->rect());
	p.setPen(pen);
    
	p.drawLine( rect.x(), 0, rect.x(), height()  );
}

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I also have to delete the previous line before to draw the new? Or the final result is a growing rectangle. How can I do?

Best,
Franco

[wysota]

What exactly is the problem?

[franco.amato]

What exactly is the problem?

Instead of drawing a horizzontally moving line it draw a rectangle that grow.

[wysota]

The rect() you get in the paint event can be an arbitrary rectangle from within your widget's coordinates. I don't think you want to paint arbitrary rectangles on your widget...

[franco.amato]

The rect() you get in the paint event can be an arbitrary rectangle from within your widget's coordinates. I don't think you want to paint arbitrary rectangles on your widget...

Sorry but I didn't get you.
So what must I do? Where my code is wrong?

[wysota]

So what must I do?

Draw a line in coordinates you want it to be drawn at, not the ones passed to you by the event.

Where my code is wrong?

Here:

QRect& rect = QRect(pe->rect());
p.setPen(pen);
 
p.drawLine( rect.x(), 0, rect.x(), height()  );

QRect& rect = QRect(pe->rect());
p.setPen(pen);
    
p.drawLine( rect.x(), 0, rect.x(), height()  );

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[franco.amato]

Draw a line in coordinates you want it to be drawn at, not the ones passed to you by the event.



Here:

QRect& rect = QRect(pe->rect());
p.setPen(pen);
 
p.drawLine( rect.x(), 0, rect.x(), height()  );

QRect& rect = QRect(pe->rect());
p.setPen(pen);
    
p.drawLine( rect.x(), 0, rect.x(), height()  );

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Sorry but I don't understand you.
How can I draw I line where I want whitout considering the rect()? How can I pass the coordinates of the line to the paintEvent?

Can you explain to me?

Best

[franco.amato]

I solved it.
The problem was the rect I passed to the paintEvent. It must completely contain the 2 lines ( old and new ). Something like this

QRect r = QRect( old_line - 1, 0, new_line + 1, height() )

QRect r = QRect( old_line - 1, 0, new_line + 1, height() )

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and pass r to the paintevent

update( r )

update( r )

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Regards,
Franco

[wysota]

No, that's wrong as well. Take a window from another application and start moving it around over your widget. You will see it's getting messy.

[franco.amato]

No, that's wrong as well. Take a window from another application and start moving it around over your widget. You will see it's getting messy.

So please let me know how must I do.


Thank you

[wysota]

So please let me know how must I do.

I already told you - draw the line in a place where you want it drawn, not in a random place. The line has some logic behind it, right? Are you able to tell exactly where the line should be drawn at a specified arbitrary moment based on the state of the application?

[franco.amato]

I already told you - draw the line in a place where you want it drawn, not in a random place. The line has some logic behind it, right? Are you able to tell exactly where the line should be drawn at a specified arbitrary moment based on the state of the application?

Yes Is exactly what I did

[wysota]

Yes Is exactly what I did

You mean now or when? Because none of the code you pasted does what I said.

[franco.amato]

You mean now or when? Because none of the code you pasted does what I said.

Here my last code:

void WaveWidget::paintEvent( QPaintEvent* pe )
{
	if( m_waveCachePixmap.isNull() )
	{
		updateWave();
	}
 
	QPainter p( this );
	QPen pen = QPen(Qt::blue, 1);
	p.setRenderHint( QPainter::Antialiasing, true );
        //wave
	p.drawPixmap( 0, 0, m_waveCachePixmap );
 
	//timeline
	p.setPen(pen);    
	p.drawLine( m_CurrentTimePosition, 0, m_CurrentTimePosition, height() );
}

void WaveWidget::paintEvent( QPaintEvent* pe )
{
	if( m_waveCachePixmap.isNull() )
	{
		updateWave();
	}

	QPainter p( this );
	QPen pen = QPen(Qt::blue, 1);
	p.setRenderHint( QPainter::Antialiasing, true );
        //wave
	p.drawPixmap( 0, 0, m_waveCachePixmap );

	//timeline
	p.setPen(pen);    
	p.drawLine( m_CurrentTimePosition, 0, m_CurrentTimePosition, height() );
}

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and the setCurrentTimePosition (as in my last post):

void WaveWidget::setCurrentTimePosition()
{
	uint newTimeValue = getCurrentPos();
 
	/* trasform time coord in widget coord */
	qreal samplesPerPixel = m_wave->getSamples() / width();
	qreal x_pos = newTimeValue / samplesPerPixel;
 
    if( x_pos == m_CurrentTimePosition )
		return; //no change
 
	QRect r = QRect( m_CurrentTimePosition - 1, 0, x_pos, height() );
	update( r );
 
	/* update current pos */
	m_CurrentTimePosition = x_pos;
}

void WaveWidget::setCurrentTimePosition()
{
	uint newTimeValue = getCurrentPos();
    
	/* trasform time coord in widget coord */
	qreal samplesPerPixel = m_wave->getSamples() / width();
	qreal x_pos = newTimeValue / samplesPerPixel;

    if( x_pos == m_CurrentTimePosition )
		return; //no change

	QRect r = QRect( m_CurrentTimePosition - 1, 0, x_pos, height() );
	update( r );

	/* update current pos */
	m_CurrentTimePosition = x_pos;
}

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Is what did you suggested to me?

[wysota]

Yes, it's much better now. The only thing I could suggest is to move updateWave() to setCurrentTimePosition() method. Your paintEvent() would then execute a bit faster which might be beneficial if complexity of your application grows.

[franco.amato]

Yes, it's much better now. The only thing I could suggest is to move updateWave() to setCurrentTimePosition() method. Your paintEvent() would then execute a bit faster which might be beneficial if complexity of your application grows.

Hi. Imagine that scenario:
1) I load an audio file -> the waveform is generated.
2) I resize the window WITHOUT PLAY THE FILE
in this case I have to update the wave so I can not move the updatewave inside the setCurrentTimePosition

Did you get me?

Best

[wysota]

2) I resize the window WITHOUT PLAY THE FILE
in this case I have to update the wave so I can not move the updatewave inside the setCurrentTimePosition

Call updateWave() from the resizeEvent() as well. It's still worth it to write another method to have the paint event not have to execute the if statement every time your widget is redrawn.

[franco.amato]

Call updateWave() from the resizeEvent() as well. It's still worth it to write another method to have the paint event not have to execute the if statement every time your widget is redrawn.

I moved the updateWave inside the resize event but the resizing process now seems slower.

What do you think about?

[wysota]

During every resize your wave is being updated. It would be wise to update it only when the user stops resizing but then it might not be worth the effort. Maybe you should stick with generating the pixmap during paint event for now until you reach a point where it becomes a bottleneck.