Native pinch gesture on a touchpad

In Dragging one DragHandler with one touchpoint we began with a detailed tour through the event delivery logic while one Rectangle is being dragged on a touchscreen with one finger. In qq-ideal-pointer-event-delivery-parallel-drags we looked at delivery of two touchpoints to drag two Rectangles. In Pinch on a touchscreen we looked at delivery of two touchpoints to one Rectangle with a PinchHandler. Now let's look at how a native gesture event from a touchpad can activate the same PinchHandler.

import QtQuick
 
Rectangle {
    id: root
    width: 400
    height: 400
    color: ph.active ? "aquamarine" : "beige"
 
    PinchHandler {
        id: ph
        grabPermissions: PointerHandler.TakeOverForbidden
    }
 
    Rectangle {
        objectName: "rect1"
        x: 50
        width: 100
        height: 100
        color: dh1.active ? "tomato" : "wheat"
        DragHandler {
            id: dh1
            objectName: "dh1"
        }
    }
 
    Rectangle {
        objectName: "rect2"
        x: 250
        width: 100
        height: 100
        color: dh2.active ? "tomato" : "lightsteelblue"
        DragHandler {
            id: dh2
            objectName: "dh2"
        }
    }
 
    Rectangle {
        objectName: "rect3"
        x: 150
        y: 150
        width: 100
        height: 100
        color: dh3.active ? "tomato" : "darksalmon"
        DragHandler {
            id: dh3
            objectName: "dh3"
        }
    }
}

Native pinch gesture on touchpad

Touchpads generally do not send QTouchEvents with discrete QEventPoints: rather, the operating system does the gesture recognition ahead of time, and the raw touchpoints are not available. Qt delivers a QNativeGestureEvent representing the entire gesture, with only one QEventPoint: the mouse cursor position where the gesture is perceived to occur on the screen. For such events (and also for QWheelEvents and a few other simple ones), so far we use simpler (more ideal) delivery logic: there's no need for distributed gesture recognition, no need for filtering, no synthesis, and little ambiguity about which handler can handle a particular gesture.

TODO diagrams for deliverSinglePointEventUntilAccepted()