Previously, if two clients were connected to the same server and one of
them was ahead of the server, the only way to rectify that situation was
for the client to get so far ahead that it stalled, as the server could
only catch up with an ahead client if all clients were ahead. That's
unrealistic. This gives the server the alternate option of demanding
that a client stall. This keeps things nicely in line even with >2
players.
Since the quirks protocol was that a core could report variable
savestate size, but the host then tells it "no", we should actually
accept the variable size quirk in netplay, since RetroArch refuses to
allow cores to actually produce variable-size states.
Previously, we could be stalled by one player but still reading data
from another, which would wedge the client because we would never act
upon the newly-read data. Now we act upon data even if we're stalled.
Fixes bugs in initial connection with high latency.
Making the netplay handshake protocol send the core and content as an
explicit command, so that the other side can (notionally) choose to load
it. That isn't implemented, of course.
The idea:
* Use a fixed number of delay_frames (eventually to be fixed at 120,
currently still uses the config variable, 0 will still be an option)
* Determine how long it takes to simulate a frame.
* Stall only if resimulating the intervening frames would be
sufficiently annoying (currently fixed at three frames worth of
time)
Because clients always try to catch up, the actual frame delay works out
automatically to be minimally zero and maximally the latency. If one
client is underpowered but the other is fine, the powerful one will
automatically take up the slack. Seems like the most reasonable system.
In resimulation mode, we only copy the buttons. The reason for this
is nonobvious:
If we resimulated nothing, then the /duration/ with which any input
was pressed would be approximately correct, since the original
simulation came in as the input came in, but the /number of times/
the input was pressed would be wrong, as there would be an
advancing wavefront of real data overtaking the simulated data
(which is really just real data offset by some frames).
That's acceptable for arrows in most situations, since the amount
you move is tied to the duration, but unacceptable for buttons,
which will seem to jerkily be pressed numerous times with those
wavefronts.
