Hmm - interesting idea Coldby.
To me, though, the main obstacle to saving selections is identifying the vertices/surfaces on reload. Take the following example, where I have these vertices in a document:
1: { 0, 0, 0 }
2: { 0, 1, 2 }
3: { 0, 2, 3 }
4: { 0, 1, 2 }
5: { 0, 0, 0 }
6: { 0, 0, 3 }
Note that vertices #1 and #5 are at the same location, as are #2 and #4.
When AC3D saves these vertices, there's no way to identify which one is which between #1 and #5 / #2 and #4 --- therefore, when we reload the vertices, it makes identification tough.
We could identify them by the surfaces to which they are attached. We may still get vertices located in the same location in a single surface (this should be a rare case).
Surfaces pose similar challenges --- we would have to store/get the vertex locations/ordering/UV/normal of the vertices in the surface, the parent object properties, and surface properties, and match those up on reload. Not insurmountable, but definitely some pain...
The other challenge is that there's no callback/interface for when an AC3D document gets saved. Meaning that, the user would be responsible for saving the .sel file. The problem arises when a user does this:
1. Saves the .ac file
2. Saves the .sel file
3. Moves a vertex
4. Saves the .ac file without saving the .sel file.
This would make any moved surfaces/vertices drop out of the selection.
So it could be done --- none of these issues seem to be outright show-stoppers --- but it will be much easier to write the plugin without a save feature
.
I'll try to get around to this plugin (without saving) soon.
Dennis