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);
}