MultiPointTouchArea: onRelease called twice?

[TOMATO_QT]

I am playing with MultiPointTouchArea in a Canvas component to make a little drawing exercise. The code below works but the onReleased event is getting called twice and I don't understand why.

From the log statements below, I see it gets called first with one TouchPoint, then again with two TouchPoints – the x and y positions are the same for all. Also the id of these touchPoints are undefined.

I don't get it. Since I define a maximumTouchPoints and am testing with just one touch (I am testing this on my laptop using a trackpad, with just one "finger".) :

• why am I getting multiple touchpoints
• why is onReleased getting called twice?
• why are the touchPoints id undefined, since I have defined my touchPoints?

---

Log statements:

qml: released 1 
qml: 	 undefined 386.66015625 207.6640625
qml: is this touch1? true

qml: released 2
qml: 	 undefined 386.66015625 207.6640625
qml: is this touch1? true
qml: 	 undefined 386.66015625 207.6640625
qml: is this touch1? true

---

    import QtQuick 2.5
    import QtQuick.Controls 1.4
    
    ApplicationWindow {
        visible: true
        width: 640
        height: 480
        title: qsTr("Canvas")
    
        Canvas {
            id: canvas
            anchors.fill: parent
    
            property real lastX: 0
            property real lastY: 0
    
            onPaint: {
                var ctx = getContext("2d")
                ctx.lineWidth = 1
                ctx.strokeStyle = "blue"
                ctx.beginPath()
                ctx.moveTo(lastX,lastY)
                ctx.lineTo(touch1.x,touch1.y)
                ctx.stroke()
    
                canvas.lastX = touch1.x;
                canvas.lastY = touch1.y;
            }
    
            function clearCanvas() {
                var ctx = canvas.getContext("2d")
                 ctx.clearRect(0, 0, canvas.width, canvas.height)
            }
    
            MultiPointTouchArea {
                anchors.fill: parent
                minimumTouchPoints: 1
                maximumTouchPoints: 1
                touchPoints: [TouchPoint { id: touch1 }]
    
                onPressed: {
                    canvas.lastX = touch1.x;
                    canvas.lastY = touch1.y;
    
                    canvas.clearCanvas();
                }
    
                onReleased: {
    
                    console.log("released", touchPoints.length); // CALLED TWICE?
    
                    var tp;
                    for (var i = 0; i < touchPoints.length; i++) {
                    tp = touchPoints[i];
                        console.log("\t",tp.id, tp.x, tp.y);

                        console.log("is this touch1?", tp === touch1);
                    }
                }
    
                onUpdated: canvas.requestPaint();
            }
        }
    }

[SGaist]

Hi and welcome again to devnet :)

Looks strange indeed. What version of Qt and OS are you using ?

[TOMATO_QT]

@SGaist

Hi – using Qt 5.5.1 on OSX 10.11.12

It doesn't seem like it should be doing this – but I am testing on the desktop, if that matters (why would it?).

I noticed another anomaly:

TouchPoint.previousX and TouchPoint.previousY are always 0 when running on the desktop but in the iOS simulator, they reprt accurate values. This seems like a bug – unless there is something really basic which I am missing.

[SGaist]

Something to investigate, did you already check the bug report system ?

[TOMATO_QT]

@SGaist

The "two release events" issue has been reported and is open: https://bugreports.qt.io/browse/QTBUG-44781

The "no "previousX, previousY" issue is there too: https://bugreports.qt.io/browse/QTBUG-41692

[SGaist]

You should vote for the bugs and add additional information if you can.

[TOMATO_QT]

@SGaist

Yeah, I did. They have been open for a while now.