Wheel Event direction changing when pressing Alt key

brai

When I use the onWheel event in a MouseArea, I get the wheel.angleDelta.y to represent my scrolling delta as expected.

When I press the alt key while scrolling, it will change the direction of the scroll from vertical to horizontal.

I.E. when the alt key is pressed, the wheel.angleDelta.x value is non-zero, and the y value is zero.

Here is the mouse area code:

MouseArea {
    id: translateArea
    anchors.fill: parent
    cursorShape: Qt.SizeAllCursor
    acceptedButtons: Qt.LeftButton

    onWheel: {
        console.log(wheel.angleDelta) // Using this to debug for now
    }

    drag: {
        target: image // Mouse Area is in an image
        axis: Drag.XAndYAxis
        maximumX: image.paintedWidth
        maximumY: image.paintedHeight
        smoothed: true
        onActiveChanged: {
             if(!translateArea.drag.active) {
                 imgTranslateX += image.x
                 imgTranslateY += image.y
                 image.x = 0
                 image.y = 0
             }
        }
    }
}

I added the drag code, just in case there is an effect here that I am unaware of, but the documentation doesn't mention anything about conflicts.

I can work around this (when alt key is pressed, look for x value instead ...) but this just doesn't seem correct?

I am running Qt 5.15.0, QtQuick 2.15, and am running the application on Windows 10, MSVC 2019 64bit.

warp

This behaviour is still not documented (Qt Bug Tracker).

The special modifier handling is implemented in QWindowsPointerHandler::translateMouseWheelEvent. A WM_MOUSEWHEEL event is treated like a WM_MOUSEHWHEEL event:

const QPoint angleDelta = (msg.message == WM_MOUSEHWHEEL || (keyModifiers & Qt::AltModifier)) ?
                QPoint(delta, 0) : QPoint(0, delta);