PS. If I remove -lGL, linking fails because of
Undefined symbols: "_glXChooseVisual", referenced from: _config in vo_gl.o "_glXCreateContext", referenced from: _setGlWindow in gl_common.o "_glXGetConfig", referenced from: _initGl in vo_gl2.o _initGl in vo_gl2.o _initGl in vo_gl2.o _initGl in vo_gl2.o _config in vo_gl2.o _config in vo_gl2.o _config in vo_gl2.o _config in vo_gl2.o _config in vo_gl2.o _config in vo_gl2.o _config in vo_gl2.o _config in vo_gl2.o _config in vo_gl2.o "_glXSwapBuffers", referenced from: _swapGlBuffers in gl_common.o "_glXDestroyContext", referenced from: _releaseGlContext in gl_common.o _setGlWindow in gl_common.o _setGlWindow in gl_common.o "_glXMakeCurrent", referenced from: _releaseGlContext in gl_common.o _setGlWindow in gl_common.o
which are not in /System/Library/Frameworks/OpenGL.framework/Libraries/ libGL.dylib nor in OpenGL, apparently. (Sorry for being so ignorant about all this...)