Hoping someone's already been through this and can point me to a solution. I'm using Ubuntu 13.10 desktop.
I had to install the libx11-dev package to get FLTK to compile, but now it fails at link time. It looks like the X11 library(ies?) aren't found. Don't know anything about X and google hasn't helped. The xorg packages are installed.
Here's the first few errors, which are followed by another couple pagefuls.
~/radiocontrol/deviation/deviation/src$ make TARGET=emu_devo10
+ Building 'emu_devo10.elf'
/usr/local/lib/libfltk.a(Fl_get_system_colors.o): In function `getsyscolor(char const*, char const*, char const*, char const*, void (*)(unsigned char, unsigned char, unsigned char))':
Fl_get_system_colors.cxx:(.text+0x25a): undefined reference to `XGetDefault'
Fl_get_system_colors.cxx:(.text+0x27b): undefined reference to `XParseColor'
/usr/local/lib/libfltk.a(Fl_get_system_colors.o): In function `fl_parse_color(char const*, unsigned char&, unsigned char&, unsigned char&)':
Fl_get_system_colors.cxx:(.text+0x2d9): undefined reference to `XParseColor'
/usr/local/lib/libfltk.a(Fl_get_system_colors.o): In function `Fl::scheme(char const*)':
Fl_get_system_colors.cxx:(.text+0x858): undefined reference to `XGetDefault'
