[Flightgear-devel] FGRUN build fails with CMake Error at CMakeLists.txt:228 (message): FLTK 1.3 is required

[Pat <pat...@gm...>]

You may have heard there is a problem building FGRUN on Ubuntu 13.04 but
not on Ubuntu 12.10.  I've attached a patch to fgrun/CMakeLists.txt.  I
consider it a workaround. It's been tested on 13.04 and 12.10

The symptom:

          The build on Ubuntu 13.04 fails with the message:
          -- Performing Test HAVE_FLTK_1_3 - Failed
          CMake Error at CMakeLists.txt:228 (message):
            FLTK 1.3 is required

          The message appears on a freshly installed and updated
          installation of 13.04, after adding the additional packages
          needed to build flightgear.

	  There is no earlier version of FLTK installed.  Other than
	  install the tools needed to build flightgear, nothing unusual
	  has been done to the libraries.

The problem:

          The failure happens when CMake tries to check that a compile
          and link using fltk 1.3 succeeds.  The compile and link
          fails  

          This is the failing section of code from fgrun/CMakeLists.txt
          at the indicated point, line 228.

           check_cxx_source_runs(
                  "#include <FL/Fl.H>
                  int main() {
                      return Fl::version() >= 1.03 ? 0 : -1;
                  }
                  "
                  HAVE_FLTK_1_3)

          	if ( NOT HAVE_FLTK_1_3 )
          		message( SEND_ERROR "FLTK 1.3 is required" ) 
          	endif ( NOT HAVE_FLTK_1_3 )
Analysis:

	  The compile of the code in the above CMakeLists.txt code is
	  failing, presumably because it does not have -ldl in the path.
	  
	  Commenting out this section of the CMakeLists.txt allows the
	  build for FGRUN to proceed.  However with only this change,
	  the actual build fails during the link phase of FGRUN for the
	  same reason.  Running the cmake and make in verbose mode
	  gives the actual error and illustrates the problem.

	  you get undefined reference to symbol dlopen@@GLIBC_2.1
	  this is in libdl.so

Possible Causes:

	  1. Sometething is amis with fltk and cmake. Has a library has
	  moved out of reach of the Find_FLTK.cmake.  

	  2. Installing something broke it on Ubuntu 13.10. 

Workaround:

	  Our CMakeLists.txt for FGRUN builds the variable
	  FLTK_LIBRARIES. I added  "libdl.so" to this variable
	  before adding two additional libraries needed for fltk. This
	  fixes the build, but not the test for fltk version 1.3 in the
	  cmake. Commenting out this test seems an acceptable
	  workaround and the build works.
Testing:
	I have tested the patch on Ubuntu 13.04 and Ubuntu 12.10.  As
	long as FLTK 1.3 is installed everything should work. 

	# get rid of previous build and install for fgrun
	rm -rf build/fgrun install/fgrun

	# get fresh copy of CMakelists.txt
	./download_and_compile.sh -d y -p n fgrun 
	
	patch fgrun/CmakeLists.txt <00000001.patch-fgrun-CMakeLists.txt

	# build without downloading a fresh CMakeLists.txt -note  -d n

	./download_and_compile.sh -d n -p n fgrun 
	

Next Steps:

	If acceptable, Commit the patched fgrun/CMakeLists.txt
	
	It would be good if someone can come up with a better patch,
	one that allows the check_cxx_source_runs to do its test.

	If anyone has a good explanation of what is really going on
	with fltk and change between the two versions, I'd like to see
	it.  We are not the only application with this issue.

	ask the fltk maintainers about this

_pat