PresentInterval is about VSync. It tells MG to draws on every VSync
(60Hz) or every second one (30Hz) or something like that.
Im pretty sure this is not equivalent behavior to xna or d3d, im not 100% but i think its the opposite.
It makes no sense at all to draw half as much as you update.
It may make sense to update half as much as you draw though.
or do some parts of your update half as much as other parts.
That only makes sense with is fixed time step off when doing your own timings.
Which in that case present interval 2 makes no sense to present every other update when you present two or twice per vsync. Though as you said controlling everything from update then it might make sense but to call draw twice as often or non stop.
See shawns reply to rim here in which he echo's that thought.
vysnc has only to do with the monitor back to front buffer swapchain timing signal (determined by the capability of the monitor itself) and if a present is allow during it or not which can cause tearing.
In truth vsync is a hardware operation its always on, the setting is if you intend to use it or not. It happens so fast and so often i believe it should always be used. Not using it with isFixedTimeStep off is a total waste of cpu and gpu time. Not using it with it on is just dumb.
While present itself is the call that tells the backbuffer to dump its contents to the front buffer.
The present interval im pretty sure was created for doing display interpolation smoothing with your extra time between updates at a steady rate though i could be wrong about that. Though i cant see any other reason for it to exist at all other then as a convenience towards that purpose.
I raised that point a while back in the issue where i noted that someone made present work that way half the updates for presenInterval two but i guess no one caught it.
There is no point to doing less draws then updates unless is running slowly evaluates to true in that case your in a cpu or gpu bottleneck anyways and your cutting things to catch up.
Though unless your making a million dollar game (like in the case of moto gp) and have tons of programmers i suppose it doesn't matter just pointing out the purpose of these things.