if (WIN32)
  define_module(sg_gui OBJECT LINKS util cohear imageprocessing opengl glew boost INCLUDES ${CMAKE_CURRENT_SOURCE_DIR}/..)
else()
  define_module(sg_gui OBJECT LINKS util cohear imageprocessing x11 opengl glew boost INCLUDES ${CMAKE_CURRENT_SOURCE_DIR}/..)
endif()

if (WIN32)
  define_module(sg_gui OBJECT LINKS util cohear imageprocessing opengl glew boost png INCLUDES ${CMAKE_CURRENT_SOURCE_DIR}/..)
else()
  define_module(sg_gui OBJECT LINKS util cohear imageprocessing x11 opengl glew boost png INCLUDES ${CMAKE_CURRENT_SOURCE_DIR}/..)
endif()

Add png as (optional) dependency
Add png as (optional) dependency
