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?