Qt for WebAssembly MultiPointTouchArea loses all touchpoints after just one is released

oe7se

If I run the following code in the browser using Qt for webassembly I can shift points around, but if one of the two is released, shifting no longer works and this console messages appears:

qt.pointer.dispatch: skipping QEventPoint(id=1 ts=0 pos=0,0 scn=869,370 gbl=869,370 Updated ellipse=(8x8 ∡ 0) vel=0,0 press=-869,-370 last=-869,-370 Δ 869,370) : no target window

import QtQuick

Window  {
    visible: true
    Rectangle {
        anchors.fill:parent
        MultiPointTouchArea {
            anchors.fill: parent
            touchPoints: [
                TouchPoint {
                    id: point1
                    onPressedChanged: console.log('point1', pressed);
                },
                TouchPoint {
                    id: point2
                    onPressedChanged: console.log('point2', pressed);
                }
            ]
        }
        Rectangle {
            width: 200; height: width;
            color: "red"
            x: point1.x
            y: point1.y
        }
        Rectangle {
            width: 200; height: width; 
            color: "green"
            x: point2.x
            y: point2.y
        }
    }
}

I tested it with versions Qt5.15.2, Qt6.4.2, Qt6.5
and different browsers, but the same error occurs all the time.

Link "test it yourself" Online live qml wasm

I debugged a little and it seems the error is in file:
C:\Qt\6.5.0\Src\qtbase\src\gui\kernel\qguiapplication.cpp

Line 2924:
    QPointer<QWindow> window = e->window;  // the platform hopefully tells us which window received the event

Line 2961:
        // If we somehow still don't have a window, we can't deliver this touchpoint.  (should never happen)
        if (Q_UNLIKELY(!window)) {
            qCWarning(lcPtrDispatch) << "skipping" << &tempPt << ": no target window";
            continue;
        }

here the window is lost.

How can i debug it further?

I also tested it with Qt under Windows, Linux, Android using diffrent versions. There everything works as expected (only using WebAssembly in the browser it doesn't)

lorn.potter

Indeed it does. This is a bug, I will report it for you.
https://bugreports.qt.io/browse/QTBUG-110941