Krita has a framework to allow painting assistant, it is the virtual version of physical tools such as rulers, compass... It allows to restrict the drawing to follow a given shape. It differs from the line/ellipse tools in that those tools gives perfect and regular results, while the assistant allows the artist to have some control on the drawing. The following blog post contains a video that show it in work:
The tool to manipulate painting assistant is limited, it allows creation and edition. This task would allow the translation of painting assistants, by showing a translate icon on the canvas (only when the tool is active), when the user click on the icon, all the handles are translated until the user release the mouse button.