A very, very basic project I’ve made is attached below 
No textures, just a pure fragment program 
You can modify the fragment program my_gui.fp and use your preffered radial gradient function, tinker a little bit there Further modifications could allow you to change the behavior of the fillings of the nodes and so on.
Notice the fragment program applies to all of your nodes separately - If you would need to use few different gradients in one GUI, you would need to think of a workaround (more GUIs e.g.) or something more sophistiticated
Regarding controling the shader from your game/app logic - it’s a little bit tricky, but you can control it from your render script, as figured out here
GUI_shader.zip (19.2 KB)
