title: Encountering 'undefined reference' and 'error adding symbols' when compiling OpenEXR
body: <p>I am installing <code>OpenEXR_Viewers</code> on <code>Ubuntu 14.04</code>. When running the <code>makefile</code>, I encounter the following error:</p>
  
  <blockquote>
    <p>/usr/bin/ld: ImageView.o: undefined reference to symbol 'glOrtho'
    //usr/lib/x86_64-linux-gnu/mesa/libGL.so.1: error adding symbols: DSO
    missing from command line collect2: error: ld returned 1 exit status</p>
  </blockquote>
  
  <p>Is it likely that my lib tool invocation is not calling GL? If this is the case, how do I set my libtool to build with GL? (Edit the makefile to see OpenGl)</p>
  
  <pre><code>Making all in playexr
  make[1]: Entering directory `/home/user/Documents/source/openexr/OpenEXR_Viewers/playexr'
  make[1]: Nothing to be done for `all'.
  make[1]: Leaving directory `/home/user/Documents/source/openexr/OpenEXR_Viewers/playexr'
  Making all in exrdisplay
  make[1]: Entering directory `/home/user/Documents/source/openexr/OpenEXR_Viewers/exrdisplay'
  /bin/bash ../libtool  --tag=CXX   --mode=link g++ -pipe -g -O2   -o exrdisplay main.o ImageView.o loadImage.o scaleImage.o applyCtl.o GlWindow3d.o -L/usr/local/lib   -pthread -L/usr/local/lib -lIlmImf -lImath-2_2 -lIexMath-2_2 -lHalf -lIex-2_2 -lIlmThread-2_2 -DHAVE_CTL_INTERPRETER=0 -L/usr/local/lib   -DHAVE_CTL_INTERPRETER=0 -pthread -L/usr/local/lib -lIlmImf -lImath-2_2 -lIexMath-2_2 -lHalf -lIex-2_2 -lIlmThread-2_2 -Wl,-Bsymbolic-functions -lfltk_gl -lfltk -lX11 
  
  *** Warning: Linking the executable exrdisplay against the loadable module
  *** libImath-2_2.so is not portable!
  
  *** Warning: Linking the executable exrdisplay against the loadable module
  *** libIexMath-2_2.so is not portable!
  
  *** Warning: Linking the executable exrdisplay against the loadable module
  *** libHalf.so is not portable!
  
  *** Warning: Linking the executable exrdisplay against the loadable module
  *** libIex-2_2.so is not portable!
  
  *** Warning: Linking the executable exrdisplay against the loadable module
  *** libIlmThread-2_2.so is not portable!
  libtool: link: g++ -pipe -g -O2 -o exrdisplay main.o ImageView.o loadImage.o scaleImage.o applyCtl.o GlWindow3d.o -pthread -DHAVE_CTL_INTERPRETER=0 -DHAVE_CTL_INTERPRETER=0 -pthread -Wl,-Bsymbolic-functions  -L/usr/local/lib /usr/local/lib/libIlmImf.so /usr/local/lib/libImath-2_2.so /usr/local/lib/libIexMath-2_2.so /usr/local/lib/libHalf.so /usr/local/lib/libIex-2_2.so /usr/local/lib/libIlmThread-2_2.so -lfltk_gl -lfltk -lX11 -pthread
  /usr/bin/ld: ImageView.o: undefined reference to symbol 'glOrtho'
  //usr/lib/x86_64-linux-gnu/mesa/libGL.so.1: error adding symbols: DSO missing from command line
  collect2: error: ld returned 1 exit status
  make[1]: *** [exrdisplay] Error 1
  make[1]: Leaving directory `/home/user/Documents/source/openexr/OpenEXR_Viewers/exrdisplay'
  make: *** [all-recursive] Error 1
  </code></pre>