[SOLVED]How to reset QGraphicsView/QGraphicsScene to display new image without overlapping with previous image

adnan

Whenever i open a new image to display it gets overlapped on previous image, thereby showing previous as well as new image.
@void aViewer::on_actionOpen_triggered()
{
/******** Opening file dialog for selecting image to be displayed **********/
fileName = QFileDialog::getOpenFileName(this,tr("Open File"), QDir::currentPath());

fileInfo.setFile&#40;fileName&#41;;                       // Storing information of image file selected

    if (!fileName.isEmpty(&#41;)                      // if file exists
    {
        image.load(fileName);                     // loading image in to a QImage object

        if (image.isNull())                       // if image does not exist display error and return
        {
            QMessageBox::information(this, tr("aViewer"),tr("Cannot load %1.").arg(fileName));
            return;
        }
        /******** if image exists display image *********************/
        displayImage.addPixmap(QPixmap::fromImage(image));            // add image to QGraphicsScene object

        ui->graphicsView->setScene(&displayImage);                    // pass image GraphicsView widget for displaying

        /****** ensure that full image is visible, i.e. scaled to viewing port *********/
        if(image.height()>ui->graphicsView->height()&&image.width()>ui->graphicsView->width())
        {
        ui->graphicsView->ensureVisible (displayImage.sceneRect());
        ui->graphicsView->fitInView(displayImage.sceneRect(), Qt::KeepAspectRatio);
        ui->graphicsView->fitInView(displayImage.itemsBoundingRect() ,Qt::KeepAspectRatio);
        }

        /******* Displaying filename as window title *******************/
        setWindowTitle(fileInfo.fileName());

        /******* Update Status Bar ******************/
        displayStatus();

    }

}@

cincirin

Maybe you want to "clear the scene":http://qt-project.org/doc/qt-4.8/qgraphicsscene.html#clear before adding new pixmap ?

adnan

It does work but the new image is not centered, it is is not displayed at centre but at right top position

cincirin

After adding the pixmap to scene, try to set new scene rect
@
displayImage->setSceneRect(0, 0, image.width(), image.height())
@

adnan

Thanks a ton!
It worked like a charm! Their is still a small issue, if you could figure it out.
If i open a picture of dimensions 128x128 it is shown as such, but if i open a picture of size 1600x1200 first and then open the previous image of 128x128 it is almost displayed as an 64x64 image, i wonder why?

cincirin

Hmmm, maybe a wrong graphics view transform ? Can you show us the code after you've added new pixmap on scene ?

adnan

Thanks a lot. Here is the new code:

@void aViewer::on_actionOpen_triggered()
{
/******** Opening file dialog for selecting image to be displayed **********/
fileName = QFileDialog::getOpenFileName(this,tr("Open File"), QDir::currentPath());

fileInfo.setFile&#40;fileName&#41;;                       // Storing information of image file selected

    if (!fileName.isEmpty())                      // if file exists
    {
        image.load(fileName);                     // loading image in to a QImage object

        if (image.isNull())                       // if image does not exist display error and return
        {
            QMessageBox::information(this, tr("aViewer"),tr("Cannot load %1.").arg(fileName));
            return;
        }

        displayImage.clear();
        /******** if image exists display image *********************/
        displayImage.addPixmap(QPixmap::fromImage(image));            // add image to QGraphicsScene object
        displayImage.setSceneRect(0, 0, image.width(), image.height());
        ui->graphicsView->setScene(&displayImage);                    // pass image GraphicsView widget for displaying

        /****** ensure that full image is visible, i.e. scaled to viewing port *********/
        if(image.height()>ui->graphicsView->height()&&image.width()>ui->graphicsView->width())
        {
        ui->graphicsView->ensureVisible (displayImage.sceneRect());
        ui->graphicsView->fitInView(displayImage.sceneRect(), Qt::KeepAspectRatio);
        ui->graphicsView->fitInView(displayImage.itemsBoundingRect() ,Qt::KeepAspectRatio);
        }

        /******* Displaying filename as window title *******************/
        setWindowTitle(fileInfo.fileName());

        /******* Update Status Bar ******************/
        displayStatus();

    }

}@

cincirin

You don't need to call "QGraphicsView::setScene":http://qt-project.org/doc/qt-4.8/qgraphicsview.html#setScene each time. Once is enough, say after you create the scene.

Also
@
ui->graphicsView->fitInView(displayImage.sceneRect(), Qt::KeepAspectRatio);
@

is enough to fit the scene in view.

I think you may set the title and status bar even if the image width or image height is less than graphics view viewport width or height. (note that you use and in condition)

adnan

Thanks, I made these two optimizations:
@ui->graphicsView->setScene(&displayImage); // in constructor@

and only used
@ui->graphicsView->fitInView(displayImage.sceneRect(), Qt::KeepAspectRatio);@

to fit the scene in view. Everything still works fine, but still the previous issue persists.

cincirin

If the image dimension is less than graphics view viewport, the graphics view remains on the old scale transformation. So if you don't fit the scene in view, show it in true size:
@
ui->graphicsView->setTransform(QTransform());
@

adnan

Thanks a lot! everything is working fine now. Thanks again!