Compiling wxWidgets takes more than an hour, so I aborted it.
Good things come to those who wait.
(Or to those with faster PCs...)
At any rate, one of the things you can do to shorten the compilation time for wxWidgets is redirecting the output. If you redirect stderr and stdout into nullspace, no text needs to be displayed (and constantly scrolled), so the CPU has more time to devote to the build. Append "1>nul 2>nul" to the make command to send the output nowhere.
The wxPack seems to work. However, every time I open and build my GUI project, it also recompiles wxWidgets, so that sucks too.
I really have no idea what you mean by "recompiles wxWidgets", and I suspect it's something other than you think. Perhaps you could give an example of what you mean.
Is there by any chance a user-friendly way of starting to design multi-platform GUI's?
Yes.
Or should I get used to searching, trying programs and reading howto's for several hours before actually starting to design the GUI?
Yes.
The concept of a modern GUI is a complex one in and of itself. On top of that, wxWidgets is an attempt to provide a basis for describing the common features of several modern GUI platforms that were
not, for the most part, intentionally designed to have anything in common. Any intermediary library has to find a balance between ease of use and power/flexibility, but all these conflicting requirements make wxWidgets' balance harder to find, and for the most part it falls on the "power/flexibility" side. This means that a fair amount of advance learning is necessary.
But as far as C++-based cross-platform GUI libraries go, I'd call wxWidgets user-friendly.
This older thread, recently resurrected, gives a decent overview of some of the other options. I call wxWidgets a good choice because it is mature and compiles on top of the native GUI API to create native "widgets", rather than drawing its own. However, other options do exist.