DragHandler::onDragChanged not reporting continously

kaixoo

When performing a drag in a QML widget that captures events using a DragHandler, (click and move the mouse), the action is not registered until dragging is finished (unclick the mouse).
Dragging should register intermediary movements (while you're moving the mouse).

Video demonstrating this issue: https://gitlab.com/advanced-effects/Advanced-Effects/-/work_items/51#note_3556028185

Relevant code:

        ApplicationCanvas {
                DragHandler {
                        onGrabChanged: (transition, event) => appCanvas.onGrabChanged(transition, event)
                        onCanceled: (event) => appCanvas.onCanceled(event)
                }

Code receiving input: https://gitlab.com/advanced-effects/Advanced-Effects/-/blob/main/src/canvas/view/viewlayers/selection_viewlayer.cpp?ref_type=heads#L132

void SelectionViewLayer::on_grab_changed(QPointingDevice::GrabTransition transition,
                                         QEventPoint event)
{
        cancel_user_selection_area();
        if (toolCtx()->selectedTool != ToolIdentifier::selection) {
                selectedObjects()->clear_all_objects();
                return;
        };

        QRectF drag_area = interactable.get_normalized_drag_area(event);

        /* Middle man work .... */

        // Finally update selection area
        m_user_selection_area = drag_area;
        update_selected_objects(m_user_selection_area);
};

JKSH

You're welcome!

@kaixoo said in DragHandler::onDragChanged not reporting continously:

I'm also looking to register when the user clicks the middle mouse button + drags their mouse. DragHandler only registers events from the left click

Set your acceptedButtons: https://doc.qt.io/qt-6/qml-qtquick-draghandler.html#acceptedButtons-prop

I see now that handlerPoint has no signals though, how am I supposed to signal when the position has changed?

handlerPoint is a value type, like date or string. The string doesn't emit a signal either when a character gets modified. Rather, the whole value gets updated.

Putting these together:

DragHandler {
    acceptedButtons: Qt.MiddleButton
    onCentroidChanged: {
        if (active)
            console.log("Centroid moved to", centroid.position)
    }
}

GrecKo

If you want to react to a drag move, you need a signal handler on the DragHandler's centroid.positionChanged.
grabChanged is only emitted when starting or stopping a drag.

kaixoo

Ohhh, I see. Thank you!
Where is centroid documented btw? It's only mentioned 3 times in DragHandler's doc page and only with some code examples, without showing a reference for the full type.

JKSH

@kaixoo said in DragHandler::onDragChanged not reporting continously:

Where is centroid documented btw? It's only mentioned 3 times in DragHandler's doc page and only with some code examples, without showing a reference for the full type.

The full type is https://doc.qt.io/qt-6/qml-qtquick-handlerpoint.html

centroid is inherited from MultiPointHandler: https://doc.qt.io/qt-6/qml-qtquick-multipointhandler.html#centroid-prop

To navigate there from the DragHandler doc page, click on "List of all members, including inherited members" which goes to see https://doc.qt.io/qt-6/qml-qtquick-draghandler-members.html

kaixoo

Thanks! I see now that handlerPoint has no signals though, how am I supposed to signal when the position has changed?

More generally, I'm also looking to register when the user clicks the middle mouse button + drags their mouse. DragHandler only registers events from the left click, is there a way I can generalize all this? Perhaps tracking the mouse position + the clicks separately? (HoverHandler + WheelHandler + Keys.onPressed?)

JKSH

You're welcome!

@kaixoo said in DragHandler::onDragChanged not reporting continously:

I'm also looking to register when the user clicks the middle mouse button + drags their mouse. DragHandler only registers events from the left click

Set your acceptedButtons: https://doc.qt.io/qt-6/qml-qtquick-draghandler.html#acceptedButtons-prop

I see now that handlerPoint has no signals though, how am I supposed to signal when the position has changed?

handlerPoint is a value type, like date or string. The string doesn't emit a signal either when a character gets modified. Rather, the whole value gets updated.

Putting these together:

DragHandler {
    acceptedButtons: Qt.MiddleButton
    onCentroidChanged: {
        if (active)
            console.log("Centroid moved to", centroid.position)
    }
}