as I've rewritten the material export logic, I owe you some explanations on how it works now. As Matej already mentionned, there's no point trying to get too accurate in Blender when exporting materials to Octane, as the way they work is too different. In order to get full benefit from Octane you definitely need to tweak them there.
My concern was anyway having a working base at import time, so a green material in Blender is green in Octane, diffuse is diffuse and so on... From the limited tests I've made, I'm pretty satisfied with the results, taking in account the simple goal to achieve and the technical limitations due to the conversion process.
So here's how it works:
[EDIT] This behaviour will be changed with next version to better match Octane's import logic. Diffuse will be set if specularity is 0, otherwise glossy or specular material.
- - diffuse material: set hardness to 1 in blender and material will be imported as diffuse, with diffuse color from Blender.
- specular material: activate transparency and select 'Raytrace'. Material will be imported in Octane as specular, with the IOR from transparency panel. Transmisison value will come from diffuse color and Reflection from specular color. Roughness will be driven by hardness
- glossy: all other materials will import as glossy, with diffuse as diffuse, specular as specular x 2 and rougthness from hardness. Octane divides by 2 the value of specularity for glossy in order to compensate for too bright material (this is due to the way Octane works, this is not a bug). However as it prevents exporting materials with 100% specularity I managed to get it x2 back in the exporter. I may make this behaviour optional in the future if anyone wants the default setting.
All textures are mapped to their respective slots: diffuse, normal/bump, specular, alpha, mirror and hardness. Some may not be used by Octane, but that's anyway inline with the OBJ format from Wavefront.Do not expect any good result if you didn't setup an UV map.
All parameters not mentionned here are not taken in account by the exporter as I don't know even know if Octane could import them.
I've attached a simple blender scene, with diffuse, specular, glossy-colored and glossy-mirror materials, so you can see by yourself.
[EDIT]: don't forget to check the 'relink' option if you want to have Octane update materials from the export!