I didn't realize you prefixed in AOI the name of your window panes by sweethome3d_window_pane and it's the simplest solution as AOI doesn't seem to handle the export of transparency to OBJ format correctly.
Thus, I updated how the glass color is computed with SunFlow rendering in the last Beta version 3.0 of Sweet Home 3D, to fix your problem.
If ever you want to handle the values in the MTL file yourself, you should have a look to MTL format specifications. For your information, the parameters used in Sweet Home 3D for transparency are:
- Kd r g b for the window color,
- d factor for the transparency factor (from 0 fully transparent to 1 fully opaque),
- Ni opticalDensity for the index of refraction.
Thank you for your patience...
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Emmanuel Puybaret, Sweet Home 3D creator
