You exist, that is enough to ruffle TheFluff. That's just his way.
Yes, GDI+ would work, and it is fast. I think DirectX or OpenGL (via
FLuaG) have better gradient support, if that matters to you. Built-in antialiasing too, I beleive. But starting from scratch is, well, be prepared for a major effort. It's the
unknown unknowns that will get you every time.
Anti Grain Geometry looks interesting, and
FLuaG even more so.
I learned a lot in this thread, thanks guys. I will have to try them both.
But if I were doing this project I think I would write a thin wrapper for ASS. As TurboPascal7 mentions, use
AegisSub with the bundled ASSDraw3 to lay out your masks (yes it does polygons, I was wrong about that). Use
Animate to tween them.