Re: [stella] 60fps vs 30fps

Subject: Re: [stella] 60fps vs 30fps
From: "Andrew Davie" <adavie@xxxxxxxxxxx>
Date: Sat, 21 Dec 2002 23:09:55 +1100
> Hmm... so if I were to create a 30mhz game I would simply not return to
> the beginning of the draw loop at the end of the overscan, but instead
> use an entire frame's worth of machine cylces performing game
> calculations before I return to the beginning of the draw loop?


No.  Please see my earlier follow-up post.

The Atari 2600 requires you to generate appropriate data for a TV frame,
which basically consists of 262 lines at 60Hz (frames/second).  You can't
get away from this.  If your game is to run at 30Hz, then you do the game
LOGIC (as opposed to the TV frame generation) once every two TV frames.  But
you still need to generate the actual frame data at 60Hz for the TV.

So your draw loop must keep running at 60mph.  Let's keep the abbreviations
correct, it's the only way we can avoid misunderstandings :)

Cheers
A



----- Original Message -----
From: "Aaron Bergstrom" <Aaron.Bergstrom@xxxxxxxxxxxxxx>
To: <stella@xxxxxxxxxxx>
Sent: Saturday, December 21, 2002 10:57 PM
Subject: Re: [stella] 60fps vs 30fps


> Hmm... so if I were to create a 30mhz game I would simply not return to
> the beginning of the draw loop at the end of the overscan, but instead
> use an entire frame's worth of machine cylces performing game
> calculations before I return to the beginning of the draw loop?
>
> Andrew Davie wrote:
>
> >The rate at which a game performs its tasks doesn't have to have a 1:1
> >correspondence to the rate of the TV frame display.  The TV frame display
> >always proceeds at 60Hz for NTSC (actually, 59.94 but who's counting) and
at
> >50Hz for PAL.  If the game does everything it needs to in one frame, then
> >it, too, is running at 60Hz (NTSC).  If, however, the game does things
over
> >two TV frames (that is, it takes two frames to update everything it needs
to
> >for one game 'cycle') then the game is running at 30Hz.  If it takes 3
> >frames for your game to do everything it needs to do (drawing, etc.) then
it
> >is running at 20Hz (60/3).   20Hz is about the low-limit of acceptable
> >animation - below that things start to get jerky and/or flickery.
> >Cheers
> >A
> >
> >----- Original Message -----
> >From: "Aaron Bergstrom" <Aaron.Bergstrom@xxxxxxxxxxxxxx>
> >To: <stella@xxxxxxxxxxx>
> >Sent: Saturday, December 21, 2002 10:07 PM
> >Subject: [stella] 60fps vs 30fps
> >
> >
> >
> >
> >>What's the basic difference between a 60 fps game vs a 30 fps game? Is
> >>it just a matter of when you turn the VBLANK on and off or is there
> >>something more... or does it not have anything to do with the VBLANK at
> >>
> >>
> >all?
> >
> >
> >>Aaron
> >>
>
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