As for the previous project, very few instructions because not much to do!
As for when you added the ellipse, circle, ... buttons in the DrawQt interface, add a new button which will act as an eraser. An icon is available in the directory data/icons: Eraser.bmp
Connect this button to the action:
void Visu2D::EraseShape();
which you’ll implement so as to erase all the displayed shapes. Don’t forget to call the method update() at the end of your EraseShape() method (so the window can be refreshed.)