QGraphicsView touch zoom

[mrjj]

Hi
Ok. odd.
i was wondering if
QGraphicsItem::ItemIgnoresTransformations

works QGraphicsProxyWidget

[Niagarer]

@mrjj
Thank you, this is a really useful one. It actually works just to say

myProxy->ItemIgnoresTransformations;

(is this really the right way to do it?)
but when zooming, the proxy also gets scaled for a moment and then jumps back to it's old scale which looks really ugly :D

[mrjj]

@Niagarer

ehh that look odd.
If you press F2 on it what does it show ?
Im not even sure what it is :) dont look like function call.

Normally it set via
http://doc.qt.io/qt-5/qgraphicsitem.html#setFlags

[Niagarer]

@mrjj
Oh, I just realized, that the mouseWheelEvent also gets triggered, when zooming via touch (!?) and in the mouseWheelEvent I did some scaling on the proxy manually. I deleted that (because I don't even need the manual scaling when ignoring tranformations, so the tip was really useful) and now I can tell:

proxy->ItemIgnoresTransformations;

doesn't work right (but it doesn't scale and jump back anymore now, my bad).

proxy->setFlag(QGraphicsItem::ItemIgnoresTransformations, true);

works perfectly well.

[mrjj]

Hi
Super.
Im not even sure why proxy->ItemIgnoresTransformations;
can compile :)
Anyway the setFlag is the way to go as you also then dont overwrite any exiting flags.

[Niagarer]

@mrjj said in QGraphicsView touch zoom:

Im not even sure why proxy->ItemIgnoresTransformations;
can compile :)

Yes, it has been one of these moments

"this can surely not work, it's nonsense... but why not just hitting ctl+r"
<<program starts>>
"uuh, wait, what?!"

[mrjj]

@Niagarer
Hi
Yes c++ is good at such moments :)
Just checked it - it reads like
proxy->GraphicsItemFlag::ItemIgnoresTransformations;
and compiler just sees
0x20;
which is perfectly valid and at same time complete nonsense :)
But hey - its valid so no complains :)

[Niagarer]

I've got one more question on this.
I have custom selection procedure in my graphicsView like this

void GraphWidget::mouseMoveEvent(QMouseEvent *event){

    if(leftMousePressed && !itemAt(event->pos())){
        if(zooming){
            //pass
        }else{
            selectingMultipleNodes = true;
            // ...
        }

    QGraphicsView::mouseMoveEvent(event);
}

selectingMultipleNodes obviously causes a selection of objects in the graph. But when I zoom, I don't want to select objects, so I added the zoom variable to it like

bool GraphWidget::viewportEvent(QEvent *event)
{
    switch (event->type()) {
    case QEvent::TouchBegin:
    case QEvent::TouchUpdate:
    case QEvent::TouchEnd:
    {
        zooming = true;
        // ...
        if (touchPoints.count() == 2) {
            // ...
        }else{
            zooming = false;
        }
        return true;
    }
    default: break;
    }
    return QGraphicsView::viewportEvent(event);
}

But when zooming via touch, almost always one finger touches the screen a little (recognizable) bit earlier that the other one. How is this normally handeled in Qt?

[mrjj]

Hi
I think people use
http://doc.qt.io/qt-5/gestures-overview.html
but i have not used it myself since im always stuck with single point touch.
I do see the issue though.
Give it some hours and see if someone has a good way of fixing this as
gestures might be overkill :)

[Niagarer]

@mrjj
Hi, thanks for the tip.

I just implemented needed methods for the pinch gesture, but I still have the same problem. The gesture is just an event and the mousePressEvent still gets triggered too.
In the mousePressEvent I do plenty of important stuff, so I need to find a way of knowing in the mousePressEvent, weather a gesture is triggered at the same time (and ignore then) or something like that.
Does someone know a workaround or how this problem is typically handeled?