Well, did not do as much as I’d expected today, mainly because most of my prog time was eaten by a very closely related topic – those *£@#ǫ]§ smooth groups! 😛
Looks like 3DS Max expects those to be bitflags values, and not simple incremental values (OBJ specifications say nothing here, so it’s more a bug from that OBJ importer than one from Blender exporter, but anyway…). Turned out to be a bit tricky, as with only 32 possible group IDs, we have to reuse them as much as possible, yet not having two adjacent smooth groups with the same bit used! Similar to the famous “four colors theorem” – current implementation tends to use five groups instead of four, though. 😉
Anyway, OBJ exporter now has both options (simple groups IDs or bitflags ones), back to the topic. Started writing the core function, most likely tomorrow it will be finished & working!