[Nouveau] Syncing to vblank for interlaced video modes

[Dirk Thierbach]

On Sun, Jun 14, 2009 at 11:56:45PM +0100, Alistair Buxton wrote:
> Stupid question: Given the presence of a register which indicates the
> current field, why can't NVWaitVSync simply wait until the end of the
> second field, by doing whatever it does twice iff it is called during
> the first field? 

Because then you'd effectively halve the frame rate in interlaced
modes, unless you somehow queue all the information for the second
half-frame.

> This method shouldn't require any patches in player software, since
> by default they treat the two interlaced fields as a single frame,

They do? I thought they they'd just treat every half-frame as a whole
frame by scaling it up vertically. Which player actually does that?

If you just combine two adjacent half-frames, you get the typical
comb-style ragged edges on fast moving objects.

Interlace *is* actually intended to give increased temporal resolution.
With nearly the same spatial resolution, because the human brain
compensates. If you treat two half-frames as one frame, you loose
that.

- Dirk