My own tool adopts a mixed approach to the layout problem : diagram-as-text, but the line breaks and the order of the boxes (entities and relations) are used as position hints. The resulting layout is constrained to an invisible grid corresponding to a left-to-right and top-to-down reading of the source.
Moreover, since there are relatively few possible grid positions, automatically rearranging the layout becomes an assignment problem, which can be solved by a simple b&b algorithm.
Obviously, this wouldn't scale, but this is just a teaching tool that I use to present small ERDs to my students.
You may test it at https://mocodo.net. Click the turning arrows symbol to draw the diagram and the shuffle symbol to rearrange it randomly.
Moreover, since there are relatively few possible grid positions, automatically rearranging the layout becomes an assignment problem, which can be solved by a simple b&b algorithm.
Obviously, this wouldn't scale, but this is just a teaching tool that I use to present small ERDs to my students.
You may test it at https://mocodo.net. Click the turning arrows symbol to draw the diagram and the shuffle symbol to rearrange it randomly.
Warning: French-flavored ERD, aka Merise MCD.