I have tried to compile cogli1 on mac following the instructions but run into the following issue: alee90 ~/cogli1/build $ make [ 26%] Built target glfw [ 32%] Built target BSpline Scanning dependencies of target cogli1 [ 33%] Building CXX object CMakeFiles/cogli1.dir/OGL/OGLManager.cpp.o /Users/alee90/cogli1/OGL/OGLManager.cpp:17:10: fatal error: 'png.h' file not found #include <png.h> ^~~~~~~ 1 error generated. make[2]: *** [CMakeFiles/cogli1.dir/OGL/OGLManager.cpp.o] Error 1 make[1]: *** [CMakeFiles/cogli1.dir/all]...