On my Mac, content is drawn only in the lower left quarter of the window because the frame buffer is 2x2 times the resolution of the window on the Retina display thingy.
I'm notccompletely fluent on the details, I just have experience with this with GLFW. And they solve this -- and explain it pretty clearly, too! -- by using glfwGetFramebufferSize instead of glfwGetWindowSize for the call to glViewport.