How to bake normal map for discontinuous mesh

Question

I'm building models for an independent game and would like to use normal maps. I started by building the low detail meshes first, which are about 4000 tris each, give or take a thousand. I built the low detail meshes in pieces to save on polycount, so when I bake a normal map onto the low poly mesh I get all kinds of errors where the high poly mesh is being projected onto the overlapping faces, no matter what bias I use.

How can I bake normal maps for these meshes? If I have to redo these to get there, what should I look out for in the future? Should I have started with a continuous mesh with all the detail and then deconstructed it to make a low detail mesh?

Answer 1

Here is a workflow you could use:

1. Build the high poly mesh first.
2. Add details as you like by adding separate meshes.
3. Build the low poly mesh over high poly mesh, using Shrinkwrap and Surface Snapping to help.
4. Separate your low poly meshes according to requirements (textures, extrusion etc).
5. Bake your maps.

This ensures correct normal and AO map bakes.

Answer 2

For future models, I second what Ali Raj said in his answer, it's usually better to build the lowpoly model from the final highpoly because this gives you the ability to follow the highpoly as closely as possible. The retopology tools of blender are quite usable and becoming better (see CGCookie: Retopology with the BSurfaces Add-on).

For your current model, I would suggest that you P-separate the main part/overlapping parts of both your highpoly and your lowpoly and put them in two different layers (each layer containing the highpoly with the corresponding lowpoly and no overlaps).

Then you can bake each of them separately, with "Clear" in the bake-settings disabled (to make sure the second bake doesn't overwrite the first one), onto the same texture and should avoid any strange artifacts.