Problem using GraphicsView

[rav]

Hi!

I am experiencing some crazy issues with graphics view.
I am trying to create an image viewer.

What I am experiencing is mixing of pointers.

The code goes like this:

//when loading an image
imagePix = new QPixmap(fileName);
scene->clear();
image = new QGraphicsPixmapItem( *imagePix );
scene->addItem( image );
 
...
 
//when displaying the image (and processing it)
    if(imagePix == NULL)
        return;
 
    //if(mask1 != NULL){
            qDebug()<<"here0";
        scene->removeItem(mask1);
 
        //delete mask1;
    //}
qDebug()<<"here1";
    int w = imagePix->width();
    int h = imagePix->height();
 
    QPixmap *temp = new QPixmap( w,h );
    QPainter painter(temp);
        painter.setPen( Qt::black );
        painter.setBrush( Qt::black );
        painter.drawRect(imagePix->rect());
    painter.end();
 
    mask1Pix = new QImage(w,h, QImage::Format_RGB888);
    mask1Pix->fill(qRgb(255,255,255));
 
    ui->bar->setVisible(true);
    ui->bar->setValue(0);
 
    int pix = w*h;
    QImage src = imagePix->toImage();
 
    //here paint what areas to reveal--------------------------------------------------
        for(int i=0; i<w; i++){
            for(int j=0; j<h; j++){
                QRgb p = src.pixel(i,j);
                if( qRed(p) - qBlue(p) - qGreen(p) >= 10){
                    mask1Pix->setPixel( i,j, qRgb(0,0,0) ); //where red - will be transparent
                }
            }
            ui->bar->setValue(((i+1)*h*100)/pix);
        }
    //--------------------------------------------------------------------------------
    ui->bar->setValue(0);
    ui->bar->setVisible(false);
 
 
    temp->setAlphaChannel( QPixmap::fromImage( *mask1Pix ) );
 
    mask1 = new QGraphicsPixmapItem( *temp );
    mask1->setZValue(2);
    mask1->setOpacity(0.9f);
 
    scene->addItem(mask1);
 
    qDebug() << imagePix << mask1Pix << "\n"<< image << mask1;
 
    delete temp;

//when loading an image
imagePix = new QPixmap(fileName);
scene->clear();
image = new QGraphicsPixmapItem( *imagePix );
scene->addItem( image );

...

//when displaying the image (and processing it)
    if(imagePix == NULL)
        return;

    //if(mask1 != NULL){
            qDebug()<<"here0";
        scene->removeItem(mask1);

        //delete mask1;
    //}
qDebug()<<"here1";
    int w = imagePix->width();
    int h = imagePix->height();

    QPixmap *temp = new QPixmap( w,h );
    QPainter painter(temp);
        painter.setPen( Qt::black );
        painter.setBrush( Qt::black );
        painter.drawRect(imagePix->rect());
    painter.end();

    mask1Pix = new QImage(w,h, QImage::Format_RGB888);
    mask1Pix->fill(qRgb(255,255,255));

    ui->bar->setVisible(true);
    ui->bar->setValue(0);

    int pix = w*h;
    QImage src = imagePix->toImage();

    //here paint what areas to reveal--------------------------------------------------
        for(int i=0; i<w; i++){
            for(int j=0; j<h; j++){
                QRgb p = src.pixel(i,j);
                if( qRed(p) - qBlue(p) - qGreen(p) >= 10){
                    mask1Pix->setPixel( i,j, qRgb(0,0,0) ); //where red - will be transparent
                }
            }
            ui->bar->setValue(((i+1)*h*100)/pix);
        }
    //--------------------------------------------------------------------------------
    ui->bar->setValue(0);
    ui->bar->setVisible(false);


    temp->setAlphaChannel( QPixmap::fromImage( *mask1Pix ) );

    mask1 = new QGraphicsPixmapItem( *temp );
    mask1->setZValue(2);
    mask1->setOpacity(0.9f);

    scene->addItem(mask1);

    qDebug() << imagePix << mask1Pix << "\n"<< image << mask1;

    delete temp;

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Please ignore the large ammount of comments - I was trying to check everything before posting here.

The app creates a second item (mask1), based on the red channel of the original pic.

The issue is as follows:
- first time I load a pic - works great
- second time i load a pic (i.e. the same one) - it all mixes up - the "picture" is being replaced with the mask (check the qDebug() output - pointer values). Instead of seeing the Pic WITH a second semi-transparent layer, i see only the second layer. Why?

I tried deleting whatever i allocate, no effect. My very temporary solution is allocating everything multiple times, the pointers differ then.

What am I missing?

Regards,
Rav

[wysota]

First of all simplify your code. Never allocate objects of type QImage or QPixmap on the heap (using "new") but rather on the stack. This will already significantly improve your code and it will be harder for you to "mix" pointers.

[rav]

Problem solved.

Solution to it:
- I used scene->clear() which deleted everything
- then I used scene->removeItem( ...) where I place an item that is supposed to be removed already in clear()

I guess the order of deleting/creating items was so unfortunate, that Qt deleted my new objects ;-)

Thanks anyway!