Hey there. There is a preview of the GUI library based on pure OpenGL.

This is not a claim for a best implementation, but an attempt to make good tool for constructing and managing GUIs. There is high-customization modular cross-version library with fully documented API.
It have simple implementation on the wide list of Minecraft versions. Now supported: 1.7.10-1.15.2.

Key features:

Uniform API - extracted general graphics components' methods
Containers - you can(and should) use relative coordinates everywhere. Creating context-free code is awesome!
Relative positioning - Alignments(like HTML alignment) and Bounds(Component Binding). More information in wiki in the bottom of the page.
Declarative-styled GUI construction code - no boilerplate, just content
Modular components structure. Combine pieces to build your dream!
Component drawing isolation - broken render can't break another
Clipping enabled by default - we use glScissor mechanism to clip drawing area and fully isolate components' rendering apart
Universal construction - StyleMap. Can define styles and draw interface elements from it. Any size, any context
Listeners. You can inject your own code to any graphics component. It should be called every time the target component updates his state
Context menus. Easy interaction with graphics components


You can get started with Github Wiki

Join our Discord! Here is the link

GExt