|size||The width and height of each face of the cubemap should be the same.|
|format||Format of underlying cubemap object.|
|mipmap||Does the cubemap have mipmaps?|
|nativeTex||Native cubemap texture object.|
Creates a Unity cubemap out of externally created native cubemap object.
This function is mostly useful for native code plugins that create platform specific cubemap texture
objects outside of Unity, and need to use these cubemaps in Unity Scenes.
Parameters passed to CreateExternalTexture should match what the texture actually is; and the underlying texture should be a Cubemap (2D textures will not work).
Native texture object on Direct3D-like devices is a pointer to the base type, from which a texture can be created (ID3D11ShaderResourceView on D3D11). On OpenGL/OpenGL ES it is GLuint. On Metal it is id<MTLTexture>.