Re: How many fps are enough (was: Athlon 64 adaptation rate?)

In article <[EMAIL PROTECTED]>, iain-3
@truecircuits.com says...
> [...]
> My understanding was that most of these games are rendering "future"
> frames.  What's on the screen represents "now".  The engine predicts
> the next buffer flip will happen in 12ms and starts a pipeline which
> computes positions making reasonable assumptions about input command
> continuity, etc, and then renders the frame.

No, that's not how it is done.

Taking the PS2 as an example, what is done is that at game frame N,
a DMA list is prepared to draw everything that should be drawn based
on the current state at frame N. At the end of frame N (at VBL time,
if you're sync'ed to the refresh rate) this DMA is kicked off to
VU1 + GS to be rendered.

On frame N+1 the VU1+GS renders this data to an offscreen buffer.
At the end of frame N+1 this offscreen buffer becomes the visible
buffer (through flipping or buffer copying). This buffer is visible
throughout frame N+2.

So, in other words, there's a two frame delay between you pushing
forward and you seeing yourself moving forward. What's on screen
therefore does _not_ represent "now", but rather "then".

Christer Ericson
Sony Computer Entertainment, Santa Monica