A few of the previous approaches are mentioned in Other work near the end. And from reading a few articles on the topic I got the impression that, yes, drawing a single shape in a shader seems almost trivial, vector graphics in general means mostly what PostScript/PDF/SVG are capable of these days. This means you don't just need filled shapes, but also strokes (and stroking in itself is a quite complicated problem), including dashed lines, line caps, etc. Gradients, image fills, blending modes are probably on the more trivial end, since I think those can all be easily solved in shaders.