Help understanding pinch/push code

Circuits

I need some help understanding how this pinch/push code works. The logic is backwards in that a pinch is zooming in and a push is zooming out. It would seem to me that I can fix this by flipping x and y in the pinchAreaStarted() function but that is just a hunch. What's happening in the actual code is escaping me, here is the code:

bool MapItem::pinchAreaStarted(QPointF, QPointF startCenter, QPointF, qreal scale, qreal, qreal angle, qreal, qreal, QPointF, QPointF, QPointF, QPointF, int, bool accepted)
{
    int x = (int)startCenter.x();
    int y = (int)(height() - startCenter.y());

    _.ui.pinch        = true;  _.ui.pinchStart        = { x, y };
    _.ui.press        = false; _.ui.pressStart        = { INT_MAX, INT_MAX };
    _.ui.pressAndHold = false; _.ui.pressAndHoldStart = { INT_MAX, INT_MAX };
    _.ui.dragging     = false;    
    OnZoom(_.ui.pinchStart, scale, angle, true);

    return accepted;
}

void MapItem::OnZoom(QPoint, qreal scale, qreal, bool first)
{
    if (first) { Q_ASSERT(events.empty()); _.zoomStart = _.CurrentZoomLevel(); }
#if 0
    qreal factor = scale < 1 ? 2 : 0.5;
    qreal zoom = _.zoomStart + (scale /*- 1.0*/) * factor;
#else
    qreal factor = scale < 1 ? 1 : .1;
    qreal zoom = _.zoomStart + (scale < 1 ? scale - 1 : scale) * factor;
#endif
    _.SetZoomLevel(zoom);
}

void SetZoomLevel(qreal zoom) {
        pThis->events.enqueue({MapItem::Z, {zoom, NAN}});
        Update();
    }

I do not understand the significance of the ( ._ )'s is that simply how you address QPoint variables?

mrjj

Hi
That looks somewhat odd ?
If you place the cursor on the _ and press F2 what is it declared as ?

Circuits

@mrjj Oh right.. okay so here's the declaration apparently it was called _ , not sure how I feel about that:

 // pimpl
    struct Data; Data& _;

mrjj

@Circuits
While valid, it seems like a odd name for it, normally the pimpl is named d
https://wiki.qt.io/D-Pointer
However in this case it seems the name _ was used.

Anyway, if you read it as
DataRef
it reads better

It seems like a pimpl impl. but im not 100% sure its used as such.

Circuits

@mrjj Agreed, either way I am not sure how these methods work exactly. I am just going to assume that switching:

_.ui.pinchStart  = {x, y}

too

_.ui.pinchStart  = {y, x}

will reverse the logic for me. If that doesn't do it than I am not sure what will. Sort of sucks the hardware is being used. Usually, when I want to learn something new about c++, I can just test things until I get a better idea of what's happening.

mrjj

@Circuits
Hi
Yes that will contain no funky side effects.
It simply say

MyDataRef.ui.pinchStart = {y, x}

so go ahead and check if it fixes your actual issue.

Circuits

@mrjj Unfortunately that didn't work. I was able to invert the zoom for the scroll wheel. The only diffrence between the zoom for the scroll wheel and the one for pinch/push is:

Used by pinch/push

    void SetZoomLevel(qreal zoom) {
        pThis->events.enqueue({MapItem::Z, {-zoom, NAN}});
        Update();
    }

and
Used by scroll wheel

    void Zoom(bool in) {
        pThis->events.enqueue({MapItem::Z, { (in?1:-1) * std::numeric_limits<qreal>::max(), NAN}});
        Update();
    }

I find it odd that both are using the same enqueue function but are passing seemingly different arguments, here is that function:

inline void enqueue(const T &t) { QList<T>::append(t); }

All I did to invert the scroll wheel functionality was to change:

(in?-1:1)

too

(in?1:-1)

so I guess I will try sending the enqueue -zoom instead of zoom. I am really just grasping at straws here, perhaps this will work.