The emulator (PVR SDK 4.0) raises an INVALID_OPERATION error during glTexImage2D when attempting to load a texture with GL_LUMINANCE8_OES internalformat. This format is required by GL_OES_required_internalformat which the emulator advertises as supported.
I haven’t tested other formats but wouldn’t be surprised if the other sized LUMINANCE formats fail as well.
This is in an OpenGL ES 3.0 context provided by the emulator running on Windows 10 on an Intel HD Graphics 5500 running OpenGL 4.3.
BTW, I am unable to log in to the Imgtec sites in Firefox. I get the error
The page isn’t redirecting properly
Firefox has detected that the server is redirecting the request for this address in a way that will never complete.
This problem can sometimes be caused by disabling or refusing to accept cookies.
I am using the self-destructing cookies add-on but this allows all cookies, deleting them only after a tab is closed.
I am writing this using Edge which has some problems rendering the forum UI.