Constraint engine

[tmpvar]

When moving a thing, it first needs to check with the constraint manager to see if it is already locked in place. If it's locked, prevent the move.

Movement can also be performed against a relationship. Examples:

distance between a segment and a point

When dragging the point, it gets clamped to be distance away from the line segment, in the appropriate direction

parallel lines

Dragging an endpoint in either line keep the point at the correct slope to ensure that it remains parallel to the other line