link fail

[  3%] Built target bin2c
[ 93%] Built target nanogui
Linking CXX executable example1
Linking CXX executable example2
libnanogui.so: undefined reference to `puglInitResizable'
libnanogui.so: undefined reference to `puglSetEventFunc'
libnanogui.so: undefined reference to `puglInit'
libnanogui.so: undefined reference to `puglWaitForEvent'
libnanogui.so: undefined reference to `puglGetVisible'
libnanogui.so: undefined reference to `puglInitWindowSize'
libnanogui.so: undefined reference to `puglEnterContext'
libnanogui.so: undefined reference to `puglHideWindow'
libnanogui.so: undefined reference to `puglShowWindow'
libnanogui.so: undefined reference to `puglGetSize'
libnanogui.so: undefined reference to `puglCreateWindow'
collect2: error: ld returned 1 exit status
libnanogui.so: undefined reference to `puglInitResizable'
libnanogui.so: undefined reference to `puglSetEventFunc'
libnanogui.so: undefined reference to `puglInit'
libnanogui.so: undefined reference to `puglWaitForEvent'
libnanogui.so: undefined reference to `puglGetVisible'
libnanogui.so: undefined reference to `puglInitWindowSize'
libnanogui.so: undefined reference to `puglEnterContext'
libnanogui.so: undefined reference to `puglHideWindow'
libnanogui.so: undefined reference to `puglShowWindow'
libnanogui.so: undefined reference to `puglGetSize'
libnanogui.so: undefined reference to `puglCreateWindow'
collect2: error: ld returned 1 exit status
CMakeFiles/example2.dir/build.make:86: recipe for target 'example2' failed
make[2]: *** [example2] Error 1
CMakeFiles/Makefile2:139: recipe for target 'CMakeFiles/example2.dir/all' failed
make[1]: *** [CMakeFiles/example2.dir/all] Error 2
make[1]: *** Waiting for unfinished jobs....
CMakeFiles/example1.dir/build.make:86: recipe for target 'example1' failed
make[2]: *** [example1] Error 1
CMakeFiles/Makefile2:95: recipe for target 'CMakeFiles/example1.dir/all' failed
make[1]: *** [CMakeFiles/example1.dir/all] Error 2
Makefile:106: recipe for target 'all' failed
make: *** [all] Error 2