What's the well-liked GUI toolkit these days for OCaml

[sanette]

it does not fully answer your question, but you might be interested in this post. The question was a bit similar, but with less sophisticated graphics. Of course, in principle you can use SDL primitives to obtain whatever you need, but it will require some work. In your case, since you don’t need animations or fancy stuff like this, I suppose it would be quite appropriate to use ocaml-cairo to produce your image. This can be integrated directly within bogue with bogue-cairo