Limit the freedom of movement of two bodies relative to each other.

Pass a constrain function in the simulation config. For example, to drag a body with the mouse, connect a mouse to a point on the box with pointToPoint:

constrain id =
    if id == "mouse" then
        Just
            (\otherId ->
                if otherId == "box" then
                    [ pointToPoint Point3d.origin pointOnBox ]


                else
                    []
            )


    else
        Nothing

Constraints are skipped unless at least one body is dynamic.

Connect a point on the first body with a point on the second body. This doesn’t limit the freedom of rotation of two bodies.

Keep two bodies connected with each other and limit the freedom of rotation. Useful for e.g. connecting a window to a window frame, or to connect a wheel to a car.

Keep the centers of mass of two bodies at the constant distance from each other.

Keep two bodies connected with each other and remove all degrees of freedom between bodies.