So just compile OSG for GLES and rewrite the glsl shaders?
For new and upcoming OpenMW branches and ports; move fast and break things!
The shaders are mostly kind of fine ish. The main problem is that lots of things don't use shaders at all, and you need shaders for GLES to work. OSG predates modern OpenGL, so by default, it uses some seriously old OpenGL that was deprecated before GLES was a thing, and so simply isn't supported on mobile GPUs. If you want to use modern OpenGL instead, you have to give up on lots of OSG features. Xyzz or Sandstranger might be able to fill in more of the details, as despite being OpenMW's main OpenGL guy, I actually don't know what is and isn't unsupported and what is and isn't workable around beyond just the shader/FFP stuff.
AnyOldName3, Master of Shadows