Current Glass code is implemented using OpenGL. 
As part of Metal Rendering Pipeline implementation, we have implemented Glass code  using Metal APIs.

As both OpenGL and Metal rendering pipelines would be available for JavaFX for some foreseeable period of time, we would need to support both the pipelines (one default, and other to opt-in by the user)

To achieve the above, we would need to refactor the glass code to have common code in base class and move OpenGL and Metal specific code to their respective derived classes.