NanoGUI builds on GLFW for cross-platform context creation and event handling, GLAD to access OpenGL functionality on Windows, and NanoVG/MetalNanoVG to draw 2D primitives.
Nanogui uses nanovg like original. I personally have no plans to add support for Metal because I have no interest in mac related things. It is a nice feature but I have no both time and hardware.
NanoGUI builds on GLFW for cross-platform context creation and event handling, GLAD to access OpenGL functionality on Windows, and NanoVG/MetalNanoVG to draw 2D primitives.