Writing OpenGL enabled GUI

Question

I am exploring a possibility to write a kind of a notebook analogue that would reproduce the look and feel of using a traditional notebook, but with the added benefit of customizing the page in ways you can't do on paper - ask the program to lay ruled paper here, grid paper there, paste an image, insert a recording from the built-in camera, try to do handwriting recognition on the tablet input, insert some latex for neat formulas and so on. I'm pretty interested in developing it just to see if writing notes on computer can come anywhere close to the comfort plain paper + pencil offer (hard to do IMO) and can always turn it in as a university C++ project, so double gain there.

Coming from the type of project there are certain requirements for the user interface:

• the user will be able to zoom, move and rotate the notebook as he wishes and I think it's pretty sensible delegate it to OpenGL, so the prospective GUI needs to work well with OGL (preferably being rendered in it)
• the interface should be navigable with as little of keyboard input as user wishes (incorporating some sort of gestures maybe) up to limiting the keyboard keys as modifiers to the pen movements and taps; this includes tablet and possible multitouch support
• the interface should keep out of the way where not needed and come up where needed and be easily layerable
• the notebook sheet itself will be a container for objects representing the notebook blurbs, so it would be nice if the GUI would be able to overlay some frames over the exact parts of the OpenGL-drawn sheet to signify what can be done with given part (like moving, rotating, deleting, copying, editing etc.) and it's extents

In terms of interface it's probably going to end up similar to Alias' Sketch Book Pro: picture.

As far as toolkits go I'm considering Qt and nui, but I'm not really aware how well would they match up the requirements and how well would they handle such an application.
As far as I know you can somehow coerce Qt into doing widget drawing with OpenGL, but on the other hand I heard voices it's slot-signal framework isn't exactly optimal and requires it's own preprocessor and I don't know how hard would be to do all the custom widgets I would need (say color-wheel, ruler, blurb frames, blurb selection, tablet-targeted pop-up menu etc.) in the constraints of Qt. Also quite a few Qt programs I've had on my machine seemed really sluggish, but it may be attributed to me having old PC or programmers using Qt suboptimally rather to the framework itself.
As for nui (http://www.libnui.net/) I know it's also cross-platform and all of the basic things you would require of a GUI toolkit and what is the biggest plus it is OpenGL-enabled from the start, but I don't know how it is with custom widgets and other facets and it certainly has smaller userbase and less elaborate documentation than Qt.

The question goes as this:

Does any of these toolkits fulfill (preferably all of) the requirements or there is a well fitting toolkit I haven't come across or maybe I should just roll up my sleeves, get SFML (or maybe Clutter would be more suited to this?) and something like FastDelegates or libsigc++ and program the GUI framework from the ground up myself?
I would be very glad if anyone had experience with a similar GUI project and can offer some comments on how well these toolkits hold up or is it worthwhile to pursue own GUI toolkit in this case.

Sorry for longwindedness, duh.

Answer 1

Have you tried FLTK? It is made with 3D graphics programming in mind and has interfaces to OpenGL. I wrote some FLTK->Scheme bindings and found the API to be real fun to work with.

Answer 2

OpenGL font support is terrible, in my experience. It sounds like you're going to have to develop all your own custom widgets anyway so don't even bother with a toolkit. You'll spend more time learning the toolkit, trying to figure out how to get that toolkit to work with OpenGL, and and trying to figure out how to make your special widgets in that toolkit than you will just rolling your own. I wouldn't give this advice in just any situation but it sounds like your application and your widget set is going to be very unique. Make a superclass for all widgets, define a draw method, even handler methods, etc., for override, and you've already done most of what those frameworks would do for you.

Also I'm sure you know this but this is an enormous project so you should initially narrow it down to a few simple objectives for a first iteration.