Everyone knows I prefer to have my UI in a browser, but I couldn't help myself and started making an in-game viewport spline editor for you kids on laptops. Not much yet, but I'm tempted to make a full widget set to replace TwAnt. I'm currently doing batching for all 2d lines, and of course I do width adjustments by their normals for visibility. You could make fancy AA/feathered lines with more primitives, but this is fine for my current uses. Always remember LINES primitive has shitty support on AMD, and it looks bad anyway so spare a quad or a couple triangles and do it right.
Playing around with some prototypes in screenshot below:
Greatly improved from earlier today after adding a windowing canvas: