Overlay

[wysota]

It doesn't matter what will you choose to paint your marks. Eventually you'll have to use QPainter anyway. You can read in Qt Quarterly about different composition modes and how do they work.

[ToddAtWSU]

I know I want to use the QPainter class, but I can just make the QPixmap object transparent and use the QPainter object to draw my points onto my overlay, right? Also, how do I place the QPixmap over the desired spot that I want. I do not see a constructor that lets me associate it with a parent widget and I don't see a function to allow me to set its location. Thanks again for your help!

[wysota]

You don't. You have to draw it using QPainter::drawPixmap().

[ToddAtWSU]

All I want to do is draw a point over my video scene. I want the user to click on a spot on the video scene and draw a red dot over it. Can I create a transparent QPixmap to place over the video and draw this, and then call QPainter::drawPoint to draw the point, or do I somehow have to associate the point onto the QPixmap and then redraw the QPixmap? Thanks again!!

[wysota]

Just prepare your pixmap and draw it. You can either use a premade pixmap or draw on it in your application.

[jpn]

Your video player is inside a QAxWidget right?
Depending a bit on the purpose of the "red points", I would probably subclass the QAxWidget, add a list of points as a member variable and reimplement a few methods:
- mouse press/release event: for adding the clicked point to the list
- paint event: for drawing all the points in the list, AFTER calling the base class implementation

[ToddAtWSU]

Yes my videoplayer is inside a QAxWidget. The users will only be putting 1-2 red dots on per frame, and when I move frames I need to reset the overlay to transparent and add any existing red points already clicked on for that frame. I am using a vector to keep track of the points that are being clicked on since I have no idea how long the video may be or how many times the user may click on one frame. So I am capturing the mouse clicks already. But I don't understand how I draw. Wysota mentioned the drawPixmap() but I am confused about this. I don't know if a QPixmap is the way to go, it was just something I saw and thought might work. I created a pointer to a QPixmap and initialized it and set its fill to Qt::transparent, but then should the QPainter object be initialized as new QPainter( this ) or QPainter( QPixmapObject )? I thought I could then just use QPainter's drawPoint function to add the new point that was clicked on. So am I misunderstanding something or what? As you can tell, I am very confused on how to go about this stuff. I have no file that contains a transparent image for QPixmap. I am just wanting to create a brand new transparent file instead of referencing one by a path. Thanks again!

[ToddAtWSU]

Any ideas why I get this error in VS.Net VC++ 7?

In my .h file I say

QPixmap *mpOverlay;

QPixmap *mpOverlay;

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In my .cpp file I say this to initialize my stuff:

mpOverlay = new QPixmap( 561, 351 );
   mpOverlay->fill( Qt::transparent );
 
   mpVideoPainter = new QPainter( this );
   mpVideoPainter->setPen( Qt::red );
 
   QRectF target( 10.0, 41.0, 561.0, 351.0 );
   QRectF source( 0.0, 0.0, 551.0, 310.0 );
 
   mpVideoPainter->drawPixmap( target, &mpOverlay, source );

mpOverlay = new QPixmap( 561, 351 );
   mpOverlay->fill( Qt::transparent );

   mpVideoPainter = new QPainter( this );
   mpVideoPainter->setPen( Qt::red );

   QRectF target( 10.0, 41.0, 561.0, 351.0 );
   QRectF source( 0.0, 0.0, 551.0, 310.0 );

   mpVideoPainter->drawPixmap( target, &mpOverlay, source );

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But I get this error when I compile: error C2664: 'void QPainter::drawPixmap(const QRectF &,const QPixmap &,const QRectF &)' : cannot convert parameter 2 from 'QPixmap **__w64 ' to 'const QPixmap &'

I have googled for solutions but cannot seem to find any. I believe my arguments are correct. Thanks!

[jpn]

But I get this error when I compile: error C2664: 'void QPainter::drawPixmap(const QRectF &,const QPixmap &,const QRectF &)' : cannot convert parameter 2 from 'QPixmap **__w64 ' to 'const QPixmap &'

That should be:

mpVideoPainter->drawPixmap( target, *mpOverlay, source );

mpVideoPainter->drawPixmap( target, *mpOverlay, source );

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[jpn]

Here's a one solution for you to consider:

class Player: public QAxWidget
{
	...
private:
	// a 2-dimensional vector; "a vector of points for each frame"
	QVector< QVector<QPoint> > framePoints;
};
 
void Player::paintEvent(QPaintEvent* e)
{
	// let the activex control to draw itself underneath
	QAxWidget::paintEvent(e);
 
	// initialize a painter
	QPainter painter(this);
	painter.setPen(QPen(Qt::red)); // red
 
	// draw all the points stored for the current frame directly on the widget
	foreach (QPoint pt, framePoints.at(currentFrame))
		painter.drawPoint(pt);
}

class Player: public QAxWidget
{
	...
private:
	// a 2-dimensional vector; "a vector of points for each frame"
	QVector< QVector<QPoint> > framePoints;
};

void Player::paintEvent(QPaintEvent* e)
{
	// let the activex control to draw itself underneath
	QAxWidget::paintEvent(e);
	
	// initialize a painter
	QPainter painter(this);
	painter.setPen(QPen(Qt::red)); // red
	
	// draw all the points stored for the current frame directly on the widget
	foreach (QPoint pt, framePoints.at(currentFrame))
		painter.drawPoint(pt);
}

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[ToddAtWSU]

I am not sure why putting the * in front helps. To me that turns the pointer into a pointer to a pointer, but for some reason it works. I thought the function wanted my argument de-referenced, but I guess not. So why when I change the Pixmaps fill color to say green do I not see a green rectangle appear over my video player? Thanks again!

[ToddAtWSU]

When I call the drawPoint function, I see nothing appear on my screen. I clicked around 15-20 times on one frame just to see if anything would appear and I do not see anything. Mine looks slightly like this where mpVideoPlayer is my QAxWidget and AzElPoint is a struct with an xPos, yPos, and frameNumber and azElPoints is a vector of these:

/*
 * Event handler for the any widget using the installEventFilter function
 */
bool VideoViewerWindow::eventFilter( QObject *obj, QEvent *event )
{
   if( obj == mpVideoPlayer )
   {
      // Mouse Button Release handlers
      if( event->type() == QEvent::MouseButtonRelease )
      { 
         AzElPoint point;
         QMouseEvent *mouseEvent = static_cast<QMouseEvent *>(event);
 
         point.frameNumber = getCurrentFrame( );
         point.xPos = mouseEvent->x( );
         point.yPos = mouseEvent->y( );
 
         if( mouseEvent->button() == Qt::LeftButton )
         {
            // If left button, place mark on overlay to indicate position
            // and store position in array at the current frame index
            azElPoints.push_back( point );
            printf( "x=%d, y=%d\n", point.xPos, point.yPos );
            mpVideoPainter->drawPoint( point.xPos, point.yPos );
 
            return true;
         }
         else if( mouseEvent->button() == Qt::RightButton )
         {
            // If right button, remove any point located in current frame
            azElPoints.push_back( point );
            printf( "x=%d, y=%d\n", point.xPos, point.yPos );
 
            return true;
         }
      }
   }
 
   if( event->type() == QEvent::Paint || event->type( ) == QEvent::Move )
   {
      if( pMediaSeeking != NULL )
      {
         repaintWindow( );
         QPainter painter( mpVideoPlayer );
         painter.setPen( QPen( Qt::red ) );
         for( int i = 0 ; i < azElPoints.size( ) ; i++ )
         {
            if( azElPoints[i].frameNumber == getCurrentFrame( ) )
            {
               painter.drawPoint( azElPoints[i].xPos, azElPoints[i].yPos );
            }
         }
      }
   }
 
   return QObject::eventFilter( obj, event );
}

/*
 * Event handler for the any widget using the installEventFilter function
 */
bool VideoViewerWindow::eventFilter( QObject *obj, QEvent *event )
{
   if( obj == mpVideoPlayer )
   {
      // Mouse Button Release handlers
      if( event->type() == QEvent::MouseButtonRelease )
      { 
         AzElPoint point;
         QMouseEvent *mouseEvent = static_cast<QMouseEvent *>(event);
         
         point.frameNumber = getCurrentFrame( );
         point.xPos = mouseEvent->x( );
         point.yPos = mouseEvent->y( );

         if( mouseEvent->button() == Qt::LeftButton )
         {
            // If left button, place mark on overlay to indicate position
            // and store position in array at the current frame index
            azElPoints.push_back( point );
            printf( "x=%d, y=%d\n", point.xPos, point.yPos );
            mpVideoPainter->drawPoint( point.xPos, point.yPos );

            return true;
         }
         else if( mouseEvent->button() == Qt::RightButton )
         {
            // If right button, remove any point located in current frame
            azElPoints.push_back( point );
            printf( "x=%d, y=%d\n", point.xPos, point.yPos );

            return true;
         }
      }
   }
   
   if( event->type() == QEvent::Paint || event->type( ) == QEvent::Move )
   {
      if( pMediaSeeking != NULL )
      {
         repaintWindow( );
         QPainter painter( mpVideoPlayer );
         painter.setPen( QPen( Qt::red ) );
         for( int i = 0 ; i < azElPoints.size( ) ; i++ )
         {
            if( azElPoints[i].frameNumber == getCurrentFrame( ) )
            {
               painter.drawPoint( azElPoints[i].xPos, azElPoints[i].yPos );
            }
         }
      }
   }

   return QObject::eventFilter( obj, event );
}

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The repaintWindow( ) function looks like this but it is mainly ActiveX functions and calls so I will not include it since it has nothing to do with Qt. pMediaSeeking being NULL means a video is not playing and we do not need to worry about repainting it or collecting data on it. I also haven't worried about implementing the right-button events yet assuming it will be fairly similar to the left-click events. Thanks once again for your help!!

[ToddAtWSU]

Is using an eventFilter the wrong way to go about this? Should I create a separate PaintEvent function? Thanks again. I thought this should draw the point, but unfortunately it does not.

[Chicken Blood Machine]

I am not sure why putting the * in front helps.

It helps because you are now giving it the argument type that it is expecting rather than the argument type that it is not expecting.

To me that turns the pointer into a pointer to a pointer

No, that de-references the pointer. See any docs on C/C++ to see the meaning of the '*' operator.

I thought the function wanted my argument de-referenced, but I guess not.

The function wants a reference to a QPixmap object, nothing more. Whether that means de-referencing your variable depends on what kind of object you are dealing with, a QPixmap or a 'pointer to QPixmap'. The following should show you how to correctly deal with both cases.

Example 1 - QPixmap allocated on the stack.

mOverlay = QPixmap( 561, 351 );
 ...
mpVideoPainter->drawPixmap( target, mOverlay, source );

mOverlay = QPixmap( 561, 351 );
 ...
mpVideoPainter->drawPixmap( target, mOverlay, source );

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Example 2 - QPixmap allocated on the heap.

mpOverlay = new QPixmap( 561, 351 );
 ...
mpVideoPainter->drawPixmap( target, *mpOverlay, source );

mpOverlay = new QPixmap( 561, 351 );
 ...
mpVideoPainter->drawPixmap( target, *mpOverlay, source );

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[ToddAtWSU]

I don't know what I was thinking, must have been having a brain freeze at that point. I have been working with C/C++ for 4+ years now, but for some reason I was thinking the & and the * were backwards when I was working on that. Probably too much programming and not enough sunlight.