Fix OpenGL rendering on MacOS Mojave for Mittsu

opengl_fix.rb

fixed_opengl = false
start_time = Time.now
renderer.window.run do
  renderer.render(@scene, @camera)

  if !fixed_opengl && Time.now - start_time > 0.5
    # Workaround for OpenGL bug on MacOS Mojave
    # Have to slightly move the window to start the rendering,
    # otherwise it stays black.
    # See: https://stackoverflow.com/a/52915794/304706
    fixed_opengl = true
    glfw_handle = renderer.window.instance_variable_get('@handle')
    x = ' ' * 8
    y = ' ' * 8
    glfwGetWindowPos(glfw_handle, x, y)
    x = x.unpack1('L')
    y = y.unpack1('L')
    glfwSetWindowPos(glfw_handle, x + 1, y)
  end
end