When comparing wxWidgets vs FLTK, the Slant community recommends wxWidgets for most people. In the question“What are the best cross-platform GUI toolkits?” wxWidgets is ranked 1st while FLTK is ranked 12th. The most important reason people chose wxWidgets is:
wxWidgets was started in 1992 by Julian Smart.
Specs
Ranked in these QuestionsQuestion Ranking
Pros
Pro Mature
wxWidgets was started in 1992 by Julian Smart.
Pro Truly native look and feel
It uses the platform's native API rather than emulating the GUI.
Pro Open source
wxWidgets can be used for free or commercial projects, at no cost.
Pro Can do custom control rendering
You can make a custom renderer using the class wxDelegateRendererNative to draw directly any standard control or using the class BackgroundWindow to use any bitmap as a control background.
Pro Forms designers
Several forms designers, like wxFormBuilder, are available.
Pro Designer
A very nice designer: wxCrafter. Free for non-commercial use/evaluation phase (without time expiration). Highly recommended if you plan to use wxWidgets.
Pro Perfect combination: wxFormBuilder + ZeroBrane (wxLua)
Lua Language can provide extra high level scripting
Pro Can use Qt on X11
WxQt is available on X11.
Pro Simplicity
It's simple design and lack of more advanced C++ features makes it easy for beginners.
Pro Fast
Well-designed widgets, coded with careful attention to rendering/execution speed.
Pro Stable
FLTK code developed more than 10 years ago still compiles and runs perfectly, without changes.
Pro Lightweight
Uses a limited and lightweight design and restricts itself to solely GUI functionality. Because of this restriction, the FLTK hello world example is only about 100 KiB.
Pro GUI designer
Fast Light User-Interface Designer (FLUID) included.
Cons
Con Android port not totally usable yet
See WxAndroid.
Con Uses GTK on X11
WxWidgets uses GTK+ on X11 desktop which well known for looking like an alien on non GTK+ desktops.
Con Has slightly heavy compiled result
Con Written in C++
Con Can be too simple for some projects
FLTK offers far fewer widgets than most other toolkits.
Con Does not look like a native application
Because it uses non-native widgets, it doesn't look like a native application on any platform.