This feature allows a user to create dimensions over a mesh: related to its vertices, allowing to change vertex position modifing it's value.
After some discusions and thoughs, We have considered dimensions part of the mesh, next to vertices, edges and faces, so they are full integrated on the mesh.
This was for performance and get a good integration
Automatic plane, axis and allow slide constraints has been set in order to allow easy modification of mesh data. Also selected vertices are afected by transform performed changing the dimension value
Changes on source are isolated via WITH_MECHANICAL_MESH_DIMENSIONS and WITH_MECHANICAL compiler definition
Changes affects to all mesh and BMesh related code.
Needs debugging on some crashes.
Dimension data is stored in .blend file, and this data will not be recognized for a non-mechanical blender binary, so if saved with it, it will be lost!
There are a lots of things to do
Allow dimension value to be fixed
Allow user to create dimensions from python
Alllow named dimensions, to be referenced by python
Allow dimensions over geometry