QGraphicsView changes on scene does not reflect

masa4

I am using QGraphicsView for showing images. First my MainSlot runs and it does its job, But i have 2 other slots according to 2 button and they re not working.
HEADER:

class MyClass{
private:
    QGraphicsScene *scene = new QGraphicsScene;
    QImage qimg;
    QImage scaledQimg;
    QPixmap pixmap;
    cv::Mat img;
}

SOURCE:

void MainSlot(){
img = cv::Mat(...);
qimg = QImage(img.data, img.cols, img.rows, img.step, QImage::Format_Grayscale8);
scaledQimg = qimg.scaled(ui->graphicsView->width() - 10, ui->graphicsView->height() - 10, Qt::KeepAspectRatio);
pixmap = QPixmap::fromImage(scaledQimg);

scene->addPixmap(pixmap);
ui->graphicsView->setScene(scene);
}

void originalSize()
{
    pixmap = QPixmap::fromImage(qimg);
    scene->update();
    ui->graphicsView->update();
}

void ScaledSize()
{
    pixmap = QPixmap::fromImage(scaledQimg);
    scene->update();
    ui->graphicsView->update();
}

Whats wrong with my code?

JonB

@masa4 said in QGraphicsView changes on scene does not reflect:

and they re not working.

It really helps if you say what you mean by this. Are we supposed to guess?

If my "guess" is "when I change pixmap in the 2 functions shown the pixmap shown on the graphics scene does not change", that would be because addPixmap(pixmap) takes a copy of pixmap, it does not make the scene have a dynamic reference to pixmap. Is that what you are asking about?

masa4

@JonB Yeah basically nothing happens when i click these 2 buttons. So you mean I should make pixmap pointer? For example:

void ScaledSize()
{
    pixmap = QPixmap::fromImage(scaledQimg);
    scene->update();
    ui->graphicsView->update();
}

here i am creating a pixmap with QPixmap::fromImage(scaledQimg) and assigning it to my pixmap. Isnt it sufficient?

jsulm

@masa4 said in QGraphicsView changes on scene does not reflect:

assigning it to my pixmap. Isnt it sufficient?

Of course not.
Why should anything change in the scene if you update pixmap variable?

JonB

@masa4
You need to alter the QPixmap which was created on the scene via scene->addPixmap().
Or, possibly, depending on your desires, remove it and put a new one instead.

masa4

@jsulm because i updating scene&graphicsview too?

jsulm

@masa4 You need to understand that your pixmap variable has no connection to your scene. If you call scene->addPixmap(pixmap); your pixmap is copied into the scene, this was already pointed out by @JonB . If you change pixmap variable later it has zero influence on the scene. You need to update the pixmap item in the scene...

masa4

@JonB yeah now worker with this:

void originalSize()
{
    pixmap = QPixmap::fromImage(qimg);
    scene->clear();
    scene->addPixmap(pixmap);
    scene->update();
    ui->graphicsView->update();
}

But original size image not sitting at the center of graphicsview. You know any trick for centerize it?

masa4

@jsulm Yep now i got the concept.

jsulm

@masa4 Now you are adding a new pixmap item all the time. I doubt this is what you want. What you should do instead: scene->addPixmap(pixmap); returns a pointer to QGraphicsPixmapItem, store this pointer as member variable and call https://doc.qt.io/qt-6/qgraphicspixmapitem.html#setPixmap on it every time you need to update pixmap.

JonB

@masa4 said in QGraphicsView changes on scene does not reflect:

But original size image not sitting at the center of graphicsview. You know any trick for centerize it?

void QGraphicsView::centerOn(const QGraphicsItem *item)

masa4

@jsulm You mean this right:
header:

...
QGraphicsPixmapItem *pix;

source:

void MainSlot(){
...
pix = scene->addPixmap(pixmap);
ui->graphicsView->setScene(scene);
}
void originalSize()
{
    pixmap = QPixmap::fromImage(qimg);
    pix->setPixmap(pixmap);
    ui->graphicsView->centerOn(ui->graphicsView->x()/2,ui->graphicsView->y()/2); //doesnt work
}

void ScaledSize()
{
    pixmap = QPixmap::fromImage(scaledQimg);
    pix->setPixmap(pixmap);
}

In this way it still works. centerize doesnt work by the way @JonB

JonB

@masa4 said in QGraphicsView changes on scene does not reflect:

In this way it still works. centerize doesnt work by the way @JonB

I never had any problem with it. Are you claiming you want to report it fails to work??

ui->graphicsView->centerOn(ui->graphicsView->x()/2,ui->graphicsView->y()/2); //doesnt work

In this way it still works

What are we expected to understand from the line saying "doesn't work" and one saying "still works"?

For your actual code (a) it's not what I suggested to use and (b) I don't know what you expect it to do.

masa4

@JonB Haha sorry for poor grammar. I mean my code work, functions work after switching to QGraphicsPixmapItem.

And i added

ui->graphicsView->centerOn(ui->graphicsView->x()/2,ui->graphicsView->y()/2); //doesnt work

this line for centering the image in graphics view. But image still not centered.

JonB

@masa4 said in QGraphicsView changes on scene does not reflect:

ui->graphicsView->centerOn(ui->graphicsView->x()/2,ui->graphicsView->y()/2);
But image still not centered.

@JonB said in QGraphicsView changes on scene does not reflect:

For your actual code (a) it's not what I suggested to use and (b) I don't know what you expect it to do.

I already wrote the above previously.