Table of contents
Introduction
Once again, after 6 long years, we manage to find a way to beat Ninja Gaiden faster than the previous movie by... ONE frame. The key to this improvement was the combination of (1) years of community-accrued knowledge of this game and its emulation, (2) breadth-first bot-driven exploration by eien86, (3) the development of an ad-hoc tool by Scumtron, that simulates how player movement and the fractional x position they spawn with affects bird position over time. We recommend reading the submission notes and comments from the previous movie(s) for an in-depth description.
Although this movie saves only a single frame, it contains considerable changes to the route and entertainment-only parts to make for a noticeably different watching experience. The changes in route contain false frames: time saves in earlier stages which were later lost due to waiting for a favorable global RNG timer. These frames convey potential time saves and were therefore kept in the movie in hopes we will find a way to overcome their limitations. The only true frame saved was achieved by brute force optimized changes in routine stage 5, as explained later.
The project was conducted in two stages. The first one (by eien86, from mid May to mid June) consisted of a full-re run of the current strats by the breadth first bot. The second stage (by Scumtron, from mid to end of June) consisted of creating the bird simulator and making numerous local improvements to the run. Although I (eien86) knew the game as a casual speedrun viewer, I had to learn the game mechanics in detail. Thankfully, Scumtron was always there to contribute with his in-depth knowledge of the game and to provide help in re-planning the route.
Emulation
Rom Information
- Name: Ninja Gaiden (U) [!]
- SHA1: CA513F841D75EFEB33BB8099FB02BEEB39F6BB9C
- MD5: 0C2CCCDA6BA6CAB7BEDE0FF05E7F6852
Emulator
- EmuHawk 2.8.0 (Core: NesHawk)
Resynchronized from the initially submitted [EmuHawk 2.7.0 + QuickNES] movie, using Scumtron's DPCM glitch detection tool, available here.
Routing Bot
- Bot: Jaffar (new version in development)
- Routing Core: QuickNES (Average Exploration Performance: 1.6M States/s)
- Platform: AMD Ryzen Threadripper 3990X Processor (64 cores, 128 threads) + 256Gb RAM
Bird Simulator
Birds accelerate towards Ryu at 1/16th of a pixel per frame and inherit the low byte of their position from the last enemy to use the slot they spawn in. These two things alone wouldn't make them terribly difficult to manipulate, but the fact that enemy routines are skipped every 16 pixels the screen is scrolled adds enough complexity that the effort of making an external tool finally seemed worth it. This tool helped in finding a two frame faster solution to 4-2, greatly assisted in almost matching the old solution to 5-1, and generally helped rule out possibilites for other improvements in various stages.
Timing
Here we show the timing of the new TAS and compare it with the older TAS. The game is structured into acts representing the story arcs in the game with bosses at the end; stages, the different playable parts of an act, and; substages, the division of a stage into multiple NES vertically stacked 'screens' to allow for the illusion of verticality within a given stage. The nomenclature goes as follows: III-2a, represents act 3, stage 2, substage a. Timing is structured as follows:
- Substage timing starts from the very first frame where Ryu is playable (typically 2 frames before he appears on screen)
- Substage transitions happen when substage number (0x006E) changes.
- Stage transitions happen when game mode* (0x002D) has a non-zero value. Alternatively, the preserved value of the A register at the start of the NMI routine that happily serves this purpose quite well.
- Act transitions happen when a Boss HP (0x0066) equals 0.
New Old Diff
Stage Initial Total Initial Total Stage Total
Boot 0 173 0 174 -1 0*
I 1 a 173 2016 174 2016 0 0
Transition 2189 277 2190 277 0 0
2 a 2466 88 2467 88 0 0
Transition 2554 747 2555 747 0 0
II 1 a 3301 970 3302 970 0 0
Transition 4271 23 4272 23 0 0
b 4294 786 4295 786 0 0
Transition 5080 22 5081 22 0 0
c 5102 97 5103 97 0 0
Transition 5199 23 5200 23 0 0
d 5222 603 5223 603 0 0
Transition 5825 277 5826 277 0 0
2 a 6102 621 6103 622 -1 -1
Transition 6723 22 6725 22 0 -1
b 6745 608 6747 610 -2 -3
Transition 7353 22 7357 22 0 -3
c 7375 1345 7379 1345 0 -3
Transition 8720 277 8724 277 0 -3
3 a 8997 82 9001 82 0 -3
Transition 9079 749 9083 748 +1 -2
III 1 a 9828 1327 9831 1322 +5 +3
Transition 11155 278 11153 277 +1 +4
2 a 11433 2029 11430 2031 -2 +2
Transition 13462 277 13461 277 0 +2
3 a 13739 85 13738 89 -4 -2
Transition 13824 744 13827 744 0 -2
IV 1 a 14568 1441 14571 1441 0 -2
Transition 16009 23 16012 23 0 -2
b 16032 75 16035 75 0 -2
Transition 16107 22 16110 22 0 -2
c 16129 392 16132 392 0 -2
Transition 16521 160 16524 160 0 -2
2 a 16681 2000 16684 2002 -2 -4
Transition 18681 277 18686 277 0 -4
3 a 18958 118 18963 118 0 -4
Transition 19076 22 19081 22 0 -4
b 19098 613 19103 613 0 -4
Transition 19711 23 19716 23 0 -4
c 19734 763 19739 763 0 -4
Transition 20497 23 20502 23 0 -4
d 20520 555 20525 555 0 -4
Transition 21075 277 21080 277 0 -4
4 a 21352 24 21357 24 0 -4
Transition 21376 748 21381 748 0 -4
V 1 a 22124 2025 22129 2025 0 -4
Transition 24149 277 24154 277 0 -4
2 a 24426 448 24431 449 -1 -5
Transition 24874 22 24880 22 0 -5
b 24896 465 24902 465 0 -5
Transition 25361 23 25367 23 0 -5
c 25384 434 25390 434 0 -5
Transition 25818 22 25824 22 0 -5
d 25840 490 25846 490 0 -5
Transition 26330 277 26336 277 0 -5
3 a 26607 406 26613 406 0 -5
Transition 27013 23 27019 23 0 -5
b 27036 449 27042 448 +1 -4
Transition 27485 23 27490 23 0 -4
c 27508 413 27513 413 0 -4
Transition 27921 23 27926 23 0 -4
d 27944 450 27949 450 0 -4
Transition 28394 23 28399 23 0 -4
e 28417 212 28422 210 +2 -2
Transition 28629 23 28632 23 0 -2
f 28652 192 28655 192 0 -2
Transition 28844 22 28847 21 +1 -1
g 28866 236 28868 236 0 -1
Transition 29102 157 29104 157 0 -1
4 a 29259 55 29261 55 0 -1
Transition 29314 748 29316 748 0 -1
VI 1 a 30062 1298 30064 1298 0 -1
Transition 31360 277 31362 277 0 -1
2 a 31637 936 31639 936 0 -1
Transition 32573 22 32575 22 0 -1
b 32595 575 32597 575 0 -1
Transition 33170 23 33172 23 0 -1
c 33193 75 33195 75 0 -1
Transition 33268 22 33270 22 0 -1
d 33290 422 33292 422 0 -1
Transition 33712 23 33714 23 0 -1
e 33735 548 33737 548 0 -1
Transition 34283 277 34285 277 0 -1
3 a 34560 430 34562 430 0 -1
Transition 34990 22 34992 22 0 -1
b 35012 133 35014 133 0 -1
Transition 35145 23 35147 23 0 -1
c 35168 1269 35170 1269 0 -1
Transition 36437 22 36439 22 0 -1
d 36459 661 36461 661 0 -1
Transition 37120 157 37122 157 0 -1
4 a 37277 62 37279 62 0 -1
Transition 37339 747 37341 747 0 -1
b 38086 102 38088 102 0 -1
Transition 38188 745 38190 744 0 -1
5 a 38932 151 38934 152 0 -1
End 39084 39086
(*) We ignore the single frame difference in boot-up between the different emulators, as these do not represent improvements in gameplay.
Act Breakdown
Act I
Stage I-1 was largely unchanged, except for the introduction of slide walk, a pure entertainment gimmick. This boss fight remained the same, except the post-kill entertainment movements were changed.
Act II
Here a change in route was proposed by Scumtron and Bumbledon where the spin slash (a.k.a. Bzzzt) weapon is used instead of the windmill (a.k.a Swag) star. This results in a frame saved from not stopping to throw the star in Stage II-2.
This route was known years ago, but then dismissed because in the end it resulted in a false frame, due to the tosser in Act III. In this TAS, however, we took it this time in hopes we would save enough frames to make the global timer work in the end (spoiler: it didn't).
At the end of Stage II-2b, the bot found a 2-frame faster way to climb the column. At this point, the new TAS is 3 frames faster than the old one.
Scum: It's a shame that there aren't more places with a ladder adjacent to a barrier block like this, though if that were the case then perhaps somebody would have found this before the bot came along.
The boss fight remained largely unchanged, except for entertainment only movements.
Act III
This act contains many changes between the two movies. Through extensive botting, we found out that the fastest way to kill the end boss is to use the firewheel: 4 frames faster than windmill star, used in the old TAS. Therefore we use the throwing ninja star to get the firewheel in III-1a:
The boss fight itself is 4 frames faster, but getting the firewheel costs time.
Throwing 3 ninja stars loses 3 frames, and the fact that ninja power remains 16, which modulo 5 is 1, means that 1 ninpo will remain at the end of the level, which loses 3 frames. Instead, we throw 5 stars and wait an additional frame to get the the tosser to cooperate. The 3 star option looks cleaner, but we needed those extra 3 frames to be during gameplay, not during the score tally, or the act IV boss would leave an extra second on the clock and cost another 3 frames. The tosser in stage III-2a acts as a gatekeeper, only allowing certain global timer values to be ones with good skips. Additionally, the old TAS loses one frame pre-shooting the windmill star before entering the boss fight (for a free pre-hit). Additionally, the firewheel route permits the rare alignment of spawn iterator, enemy subpixel, and ninja position that saves a frame by jumping over the guy at the end of the level.
At the end of all these changes, the new TAS ends up with a 2 frame advantage.
Act IV
Here we implemented Ninja Gaiden's hidden secret: *Train mode*. It activates whenever Ryu is in tracks.
Scum: Through the BirdSim I found that if the boosting bird inherited a subpixel of five or six sixteenths then the extra frames lost manipulating it weren't necessary, saving 2 frames. I also determined that turning around (needed to deal with the pursuing green ninja, costs 2 frames) after the bird's first pass and before its second pass was required to get it to meet Ryu in the right spot. That rules out the alternative of turning around when landing on the mine cart before the bridge, which would only cost 1 frame.
This boss fight remained the same. Post boss kill entertainment movements were changed.
Act V
Stage 5-1 contains a tosser whose ending projectile position determines the path of the bird we use to skip parts throughout the level. Only a few global timer values give the correct value, so we needed to either give up those four frames won before to get the same timer as the old TAS or find an alternative. The use of the bird simulator was crucial in finding a way to exit the stage with some of the locally saved frames. In the end all it took was giving up half a pixel in the wall climb after the first boost and giving the bird an xsub of eight sixteenths to leave 5-1 without losing a frame. Unfortunately that half-pixel was enough to affect the timing of a bat spawn, requiring an extra special attack which meant losing 1 frame later on.
Stage 5-2 contains the only true frame saved. By not grabbing the 10 ninpo in the middle, it is possible to end half a pixel to the left, allowing us to end the level one frame faster:
The problem remains, however, that now we have 10 fewer ninpo and we need to save two spin slash uses. The first spin slash was saved by the bot, which discovered a way to finish V-2c as fast as the old movie, but also taking +5 ninpo at the end.
The remaining 5 ninpo was saved, as suggested by Scumtron, by not killing the last two enemies in stage V-3f.
The boss fight was unaltered, except for the entertainment movements at the end.
Act VI
The tosser in VI-1 uses a bad pattern when arriving with -2 frames here, and we had to lose one frame beforehand to get the good pattern. Otherwise, the only difference in the last act was the need to adjust some use of ninpo due to the difference in enemy patterns due to arriving one frame faster. However, overall everything remained the same, except for some entertainment movement.
Future Work
The fact that only one frame save persisted after so much work speaks volumes to the level of global and local optimization this movie has had throughout the years. We tried our best to bring all local saves towards the end of the game, but the sheer presence of randomness in the tossers, made this very difficult.
False Frames
As shown above, we found a bunch of false frames. These represent local optimization opportunities that should be considered by anyone wanting to improve this movie. How to fit these in a global plan that keeps those savings will be key to further improvements.
Pre-Kill
Joecurr discovered a way to pre-kill enemies or projectiles as soon as they spawn (see this video). This can be done by throwing a special attack timed to kill an enemy on the frame it exits the screen (or, in some cases, a sword attack as an enemy exits the top of the screen). This triggers the 'death' bit which isn't cleared because the explosion animation is not played. Therefore, the next enemy that uses the same slot will instantly die. We haven't found a use for this in a TAS yet, but could serve in the future to fix enemy patterns and fit the false frames.
Knuckle's Skywalk Glitch
This is a bug where a projectile shooting enemy is manipulated to enable sky walking. See the video
Acknowledgements and Attributions
The bulk of this TAS work was done by the authors. We have received support from the Ninja Gaiden speedrunning community, especially Bumbledon and Joecurr, and blacksquall. It seems like a great coincidence that we finished the first version of this TAS the same day Arcus and TheRetroRunner got their PBs (11:35 and 11:34, respectively. GGS!).
Suggested Thumbnails
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feos: Claiming for judging.
feos: Replacing the movie and accepting over [3223] NES Ninja Gaiden by Scumtron, MESHUGGAH, feos, Xipo, Marx in 10:50.36.
Publisher, please use the second movie from that post for encoding.
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