secrets

Random damage in SF2

Everyone knows there are random elements in the SF2 engine, including the amount of damage and stun done by most attacks. But what kind of randomness, exactly? Here are the general rules:

attack type	random dizzy	random damage	lifebar scaling*
non-throws	yes	yes	yes
normal throws	yes	no	yes
multi-hit throws	yes*	no	yes
command throws	yes	depends*	yes

• I didn't examine lifebar scaling in depth, but a little testing can confirm T.Akiba's findings. Just set the opponent's life to 30 and see the difference.
• Some holds like Blanka's and Balrog's always do no dizzy.
• Throws do fixed damage except the following:
  • Gief's SPD (SSF2 and SSF2T versions only)
  • Gief's close 360+K, 2nd hit
  • Gief's far 360+K
  • Gief's super, 3rd hit
  • Hawk's super, 2nd hit
  • Vega's super, 3rd hit
  • Honda's oicho, both hits

Now for the details. To reveal the exact damage and dizzy formula for all attacks and help compile more accurate attack data, I developed the following breakpoints for use in the MAME debugger:

breakpoints	helper Lua script
(local copy)	(local copy)

You run MAME with the -debug switch on, then copypaste each of the bp lines for your game into the console. Then anytime either player gets attacked, the damage and stun info is displayed there. Since the FBA/MAME-rr Lua implementation doesn't support breakpoints, there's no pure-Lua way to get the formulas. What the helper script does is it prints out damage/stun/timeout dealt whenever someone gets hurt. You can use it to more easily verify that the formulas jive with the real figures.

(There's supposed to be a way to enter multiple commands at once, but it doesn't work. Also, these will only work on the current parent ROMs, not clones. However, every ROM address is given relative to the breakpoint address, the pc, so getting these to work with a clone should only require offsetting the bp by a constant value.)

How random damage works: there's a base damage for every hit, then a random value is added. The random values are looked up from a table of 32 possibilities, with the actual one selected determined by the output of a pseudorandom number generator. The sum is then scaled down by a certain factor and rounded up to produce the final damage.

The lookup table is dependent on the attack, and all the relevant random number tables are included in the bp file. The scale factor, however, is dependent on the opponent: it's a defense rating.

How to get frame data with Macrolua

Wrote up a hands-on guide here:

http://code.google.com/p/macrolua/wiki/FrameDataExamples

I'll later describe a faster method I've been working on, but it's important to establish the fundamentals in order to have a standard to check against. There's also gonna be a separate wiki page for more general script examples.

The current frame data examples are pretty basic. Feel free to suggest any other kinds of tests, particularly with other types of games.

There should be a new version of MAME released in the next couple weeks, which means Pugsy will update, which means I won't have to refer to a message board thread for the cheat codes that remove frameskip. The ST code is pretty much required to follow along on those first examples.

CPS2 background removal codes

Thanks to some info passed to me by felineki, I've developed some "cheat" codes to hide the background layers and background sprites of some CPS2 games:

xmcota, msh, xmvsf, mshvsf, mvsc, sfa2, sfz2al, sfa3, vsav, vhunt2, vsav2

• FBA format
• MAME format

Setting the NeoGeo BIOS in MAME

NeoGeo Games by default run in arcade (MVS) mode, but some features like training mode, stage select and in-game pause are only available in console (AES) mode. The mode depends on what BIOS the game is run with. Switching in FBA is as easy as picking from the Set dipswitches menu, provided you have the desired BIOS ROMs.

To pick a BIOS in MAME, it must be specified on the command line with -bios followed by the name. To see the list of recognized versions, run the game with the -listxml (or -lx) command. You can pipe the output to filter out the unrelated lines like this:

mame garoup -lx|find "biosset name="

Battle Master

Battle Master aka Battlemaster is a fantasy RPG emphasizing realtime combat between squad-sized armies and played from an overhead perspective. It was created in 1990 by long-defunct British developer Mirrorsoft, originally for PC systems and later ported to Sega Megadrive/Genesis, with its PC-ish interface intact.

Before there was Fallout and Diablo and Baldur's Gate, there were games like Battle Master. It's not a good game. It's ugly, the AI is horrible, and the lag is insane. The cover is badass though.

No, I didn't get the free poster.

I was introduced to it a long time ago by an older friend named Zach, who later gave me his collection. Zach didn't exactly have the best taste in video games. They included Might and Magic 2, The Immortal, and Sword of Sodan, the last of which I think is the worst of all the hundreds of games I've played. (Incidentally all of those are Western PC to console ports.) I suppose Zach wasn't being generous so much as cleaning house.

When you write a guide for an obscure game, you can expect a trickle of desperate feedback over the years. Players who need help have nowhere to turn but you, since there isn't any other source of info out there. The latter part of Battle Master gets really hard and it's unclear what you are supposed to do to survive.

Incited by an email inquiry last month, I embarked on the questionable task of renovating a gamefaqs guide, originally from 2004. Gens-rr has a trace function that reveals every instruction that the CPU performs, and Lua functions that can be triggered by specific memory or instruction addresses. The trace dumps are similar the output of MAME's debugger, which I've been using to study hitboxes. I applied my new debugging ability to studying the differences between the weapon and armor types, finding out what the mysterious rings and jewelry do, and deriving the formulas for damage and chance-to-hit.