In reponse to this,
All sorts can go wrong when you transfer from one 3D environment to another - vertex winding, scale, normals, etc. Never heard of folding in half though. In Blender, the world up axis is positive Z, (0.0, 0.0, 1.0). In Processing, the world up axis is negative Y (0.0, -1.0, 0.0). Make sure your model isn’t upside down. Add some lights to your Processing sketch, then make sure it isn’t inside-out like a sock.
Problems are easier to fix in Blender than Processing, so go back to Blender, make sure your faces are properly oriented. They will be blue if they’re right; red if they’re flipped wrong way 'round.
If any faces are red, you can fix them by going into edit mode (press
Tab), then going to
Mesh > Normals > Flip.
Normals and a face’s vertex winding are two separate, but related concepts, so the menu organization is a bit whack. But whatever.
The quickest way to fix your normals is to let Blender do it for you with
Shade Smooth or
Shade Flat while you’re in object mode.
When you export the .obj, double check the export settings, particularly the Transform section (press
N to toggle the settings on and off).
I forget what will work best for transfer to Processing. If nothing here works, you may have to rotate or scale by -1 (always double check face orientation and recalculate normals after doing the latter).
Hope that helps.