+enabled opengl && { check_lib GL/glx.h glXGetProcAddress "-lGL" ||
+ check_lib2 windows.h wglGetProcAddress "-lopengl32 -lgdi32" ||
+ check_lib2 OpenGL/gl3.h glGetError "-Wl,-framework,OpenGL" ||
+ check_lib2 ES2/gl.h glGetError "-isysroot=${sysroot} -Wl,-framework,OpenGLES" ||
+ die "ERROR: opengl not found."
+ }