Last few weeks Morten Mikkelsen and me were working under baker, which could bake normals directly from mesh with multi-resolution modifier without using much of additional memory. Now, we've got quite usable patch.
To use new baker you should choose "Sculpt baker" in Baker panel, select object with sculpted data on multires modifier, choose subdivision level you want to bake to and hit "Bake". Note, that mesh should be unwrapped and texture should be assigned to this UV map.
Baking happens in "locked" mode, so there'll be no UI refresh during baking (that's the downside of not using additional memory).
Some additional work is needed before we could say "yep, it's finished and could be commited", but you could alreayd have fun!
ubuntu 11.04 64bits
I gave it a quick try with a sculpted default cube.
Having a good result is easier than with a selected to active workflow.
It does not work correctly when multires preview level is lower or higher than bake level.
Next version of patch: with some minor fixes and implementation of heights baking.
Baker could now switch to job-related work and "Cancel" button would be shown for it, but it still needs object editing (and probably 3dview refresh freeze), so this option is disabled by default.
After Brecht's review some things were changed. fixed, improved:
- Now baking happens from highest level of multires to current viewport level
- To bake using sculpt-baker you should:
1) choose what you want to bake (normals/displacement).
2) enable "Bake from Multires" checkbox.
- Baking became thread-safe due to it shouldn't share hi-res mesh used in viewport and holds it's own hi-res and lo-res versions (lo-res doesn't add so many memory overhead). Now you've got progress bar and "Cancel" button.
- I've found incorrect calculation when using "Smooth Heights" option. Not it should behave correct.
- Now baking happens for all selected objects (be careful due to hi-res mesh for each of them would be stored in memory at the same time).
Looks like list of major things is over.