The oren_nayar_diffuse_bsdf closure in OSL had two issues: - It broke when used with roughness of zero - It only used the provided albedo for energy compensation, so it still required the user to multiply with the albedo Therefore, this handles the zero roughness corner case and includes the albedo in the closure weight. This makes no difference when using the closure through the Diffuse or Principled BSDF nodes, only for custom OSL shaders. Pull Request: https://projects.blender.org/blender/blender/pulls/133597