- [MTLDrawable presentAtTime:] syncs to display vsync. To support VK_PRESENT_MODE_IMMEDIATE_KHR while using VkPresentTimeGOOGLE::presentID, only call presentAtTime: if VkPresentTimeGOOGLE::desiredPresentTime has been explicitly set to a non-zero value. - Clarify initially clearing MVKImagePresentInfo to all zeros.