Moving a graphics scene in a graphics view on middle click

[l0drex]

I am trying to move the scene of a QGraphicsView when clicking the middle mouse button.
So I subclassed QGraphicsView and have overwritten mouseMouseEvent. I have a vector for the movement like this:

const auto movement = mapToScene(event->pos() - lastCursorPosition);

Now, my issue is that translate() uses the transformation anchor. Here is what happens with each anchor:

• NoAnchor: Movement is correct, but always starts in the top left. This is unusable for me, since I want to translate the current view.
• AnchorUnderMouse: Movement is way too fast. When I move the mouse, I move the anchor, which makes the movement way bigger than I wanted
• AnchorViewCenter: Nothing moves, because the center is always centered.

Now, I tried the following things:

• use NoAnchor and translate to the current mouse position. No effect since the next translate() moves back to top left
• use AnchorUnderMouse and translate with 0 / 1 / a fraction of the vector. Movement still way too fast.
• set DragMode to ScrollHandDrag and send a mouseMoveEvent(newEvent) to the parent, overriding buttons with LeftButton whenever a MiddleButton is received. No resulte since parent seems to be prioritized.
• change the position of horizontal and vertical scrollbars instead of using translate, as Qt does with ScrollHandDrag. Not possible, since I cant access the necessary functions.

So, my question is: How do I move the scene of a view when the user drags the mouse with middle button pressed?

If needed, here are the interesting functions:

void GraphicsView::mousePressEvent(QMouseEvent *event) {
    if (event->button() == Qt::MiddleButton) {
        setCursor(Qt::DragMoveCursor);
        lastCursorPosition = event->pos();
        event->accept();
    }
    QGraphicsView::mousePressEvent(event);
}

void GraphicsView::mouseMoveEvent(QMouseEvent *event) {
    if (event->buttons() == Qt::MiddleButton) {
        // FIXME scene is always moved from the top left corner
        setTransformationAnchor(AnchorUnderMouse);
        const auto movement = mapToScene(event->pos() - lastCursorPosition);
        translate(movement.x(), movement.y());
        event->accept();
    } else
        QGraphicsView::mouseMoveEvent(event);
}

void GraphicsView::mouseReleaseEvent(QMouseEvent *event) {
    unsetCursor();
    QGraphicsView::mouseReleaseEvent(event);
}