[Tuxnes-devel] saving the "state" of the game

[Jason D. S. <jas...@ya...>]

I recently started using tuxnes again (good work with
the recent improvements, BTW), and it looks like
TuxNES has no "save state" feature like many other
emulators do.  (It's possible I missed it, in which
case please correct me.)

So, I set out to implement this.  I created two
functions, savestate() and restorestate().  I
arbitrarily picked keys F11 and F12 to link to them. 
(These were obviously unused, while most other logical
keys to use for this were in use.  I only have
bindings for X11 at the moment.)

Currently, the "state" that is saved includes only the
program counter, stack pointer, and the first (only?)
32k of RAM.  Amazingly enough, this more-or-less
works!  I had thought that additional registers (which
I saw reference to in the dyn-rec file) would have to
be saved as well, but I guess they're placed somewhere
in the RAM pages when not in use (?).  All this took
very little time (~20 minutes).  I can now save and
restore the state, and everything works fine (except
as below).  (I quickly racked up tokens in the Dragon
Warrior 4 casino using it.  Ahh, cheating...)

A somewhat major problem is that graphics are not
immediately updated after the restore.  At first I
thought this could be solved by forcing a refresh, so
I set the "needsredraw", "redrawall", and
"redrawbackground" flags to force a redraw.  When this
didn't work, I immediately realized my error - of
course the graphics are drawn by the game's code, so
the graphical frontend (X11) has no way of knowing
what to draw until the game chooses to redraw.  This
suggests that the image on the screen must also be a
part of the saved state.  However, this presents a
problem because it is frontend-specific: the code for
creating a digital segment for the image will be
different between different graphical systems.  More
importantly, the data format itself will most likely
be different (unless pains are taken to convert it to
a standard format) - this is already the case with
screen shots.

I don't have a patch to give you right now, since my
computer is currently disconnected from the internet
(a DSL problem); this is the same reason why I'm
posting from this random Yahoo account (for which I
apologize, especially if it kills the formatting).  In
a few days I should have it fixed.

Another goal of this subproject would be to be
compatible with other emulator saved-state files. 
However, a cursory web search won't tell me what the
format for NESticle saved state files is.

jason short


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