DESTROYING Gravity in Super Mario World - Game Genie: Uncorked Episode 2 

In TMNT 4 Turtles in Time, different kills against foot soldiers award different point values.

I'd love to see some digging into SNES Shadowrun damage calculations. They can get funky, even when not using cheats. For instance, there is a mini-boss later in the game that can be killed over and over (a Naga) so long as you do not pick up its item drop. This makes for an obvious grinding spot, but more strangely, sometimes the enemy dies in the first hit, so long as you draw your weapon and hit them very soon after entering the room. Almost as though the enemy health is added incrementally (like Earthbound).

Battletoads double dragon on nes had the main menu flicker with the music when using the infinite lives code. I would like to know why.

(Besides this, really love your content! been binging all the videos last couple of days!) slight little complaint: In your blue overlay box, please add zeroes in the fractions! now without the zeroes it just keeps flickering like crazy, giving me an headache loll 165.4375 165.445 165.54 165.6 165 could be: 165.4375 165.4450 165.5400 165.6000 165.0000 (i know writing it out like this seems useless, but i wanted to provide a visual aid of what is causing the flicker for anyone that didnt understand my complaint)

Thank you so much!

cave story also has a similar system to this, but with a slight difference: rather than simply decreasing gravity when jump is held, gravity is decreased if jump is held... *and* quote is moving upwards, so the downward part of the jump is always consistent, it's the upwards part that is controlled by holding/releasing jump

I feel like it is a natural instinct for a gamer to mash the button and hold it in attempt to stay in the air for a longer period of time, and programming using the button pressed/not pressed to change physics is perfect.

At first I was like "whaaat" - but got to think.. And during the really long jumps, if you let go of the jump button while at peak height.. You'll simply drop into the pit. So people probably (very quickly) learn to hold the jump button for as long as possible. :D Very insightful video!

There's also ways to take damage while down in a hole and then jump back out. If your life is depleted while off screen you don't exit the level despite hearing the dying noise. To this day I haven't seen anyone else replicate it though. But I used to use it to make myself invincible in the levels where it worked.

@@flameshana9 Yeah I did that too! The music would stop and you wouldn't be able to shoot because you had no "ammo" for it, but you could still use boss weapons.

There are a few ways of handling jump height. I had to look into it a while back for a game I'm working on and ended up implementing a system similar to this one, with the exception being that when the Y velocity turns positive the full gravity is always applied regardless of whether or not the jump button is pressed. This gravity-manipulation allows the player some control over jump height, but it's imprecise. The character will continue to ascend even after the jump button is released, albeit with gravity decelerating them at a faster rate. This works for Mario because your main concern with that game is landing on a precise position on the horizontal axis, but for something like Mega Man, where one of the main skills that the player needs to master is shooting at a precise vertical height, that wouldn't give the right amount of control. I haven't done a deep-dive into how Mega Man handles jumping, but just from playing the game it appears that gravity is applied at a constant rate as the character ascends as long as the jump button is held, but the vertical velocity is instantly reduced to zero when the button is released. Mega Man begins accelerating downwards at this point but since he's starting from zero there's a few frames where the downward velocity is minimal, giving the player a chance to fire a few shots. After some practice the player will get into a habit of jumping, releasing the jump button and immediately firing when they're in-line with their target, and then falling to the ground to repeat the cycle. And, of course, there are games where the jump height is fixed, even later into the 8- and 16-bit eras where controllable jump height had become common. There are obvious examples like Ghosts 'n Goblins and many of the Castlevania games where your entire jump path is fixed, but even games that allow you horizontal control while in the air will still sometimes restrict you to a specific jump height. Ninja Gaiden and Contra both worked this way.

Retro Game Mechanics Explained has a video that goes over the decoding for all the various Game Genies. The SNES and Genesis codes do use what look like hex values, but most of the bits are scrambled and I believe so are the mapping of 0-F to the raw binary values.

Heck, how much patreon dollars do i need to spend to make this happen :D

Hey, I appreciate the comment. A few things here on the GGU series - It is meant to be simpler, shorter, and easier to produce. When I put that code box in the FF2 episode, I didn't realize just how much time that was going to add to production. Admittedly, it was also a bit more time consuming as I also elected to show both revisions of code and their ROM locations. I like to use Behind the Code (and Talkin' Code if I ever revive that) to show any code and Game Genie Uncorked for explaining concepts/logic behind GG codes. I've received feedback from both sides ("More code!" "Less code!!"), and having separate series helps manage expectations. The programmer box at the bottom of the first episode was meant to appeal to the people that enjoy code without me needing to really reference it in narration. I may include it in future GGU episodes when possible - not ruling it out.

@@DisplacedGamers That's totally fair - I think I've left comments on other episodes saying "gee I wish there was more content". As someone who is not a video producer, I take for granted just how much production time can go into a single episode, and I appreciate the desire to have a series with a (potentially) broader appeal and which takes less time to put together. Thanks for responding! (Also P.S. I loved Talkin' Code as well so of course I'm rooting for it to return 😄)

Thank you! So the original GG codes point to the place in the ROM where the default gravity for jump button held is stored. The codes change what that value is. You can add a breakpoint for when that value is loaded from the ROM and then follow the logic that uses it. You can then see what RAM value is referenced (ex: Mario’s Yposition) when applying that value/a product using that value. That’s likely a good amount of information to begin to comment on the assembly code inside the subroutines containing gravity logic. In short - use the Game Genie code as a starting point and then just keep checking what uses the value in order to understand the routines.

@@DisplacedGamers Thanks for the reply! I think my original question was poorly worded. For instance, there's a game I'm working on hacking (GI Joe The Fate of Atlantis) because I stink at it :) I was able to come up with codes for infinite ammo, but I'd like to try and do mega-jumps like in your video today. I'm curious what a general procedure would be to find these constants. For instance, is there some way in Mesen to take snapshots of memory and compare before/after? Do you have Mesen best practices for analyzing things? I love the videos!

@@GEfromNJ Whatever gives you memory dumps and breakpoints. Watching what values change in memory in certain circumstances, in this case jumping, will point you in the right direction. From there you may be able to pick it out based on how the variable changes throughout the jump. Finding the "source" of the gravity variable may require a code walk - you probably need to do a breakpoint on when the speed/velocity changes and look up a line or two to see where the source of the gravity value is.

It's far easier to watch memory dumps on the NES than newer consoles due to the limited amount of RAM.

@@GEfromNJ So I like to watch the RAM for NES games, find the player X/Y location by moving around and jumping. I set a breakpoint for something like the Y-Position, disable it, slow the game down, jump (either using the controller or the controller feature in the debug window), and then enable the breakpoint to see what is influencing the value of that variable in RAM. I continue to work backward from there depending on what I am trying to find.

It's so simple in hindsight, right?

That's so weird. That same SNES GG you have works on the earlier, non-1chip revisions, though?

Thanks!

I assume it is just for Mario/Mario with Yoshi. That said, I suppose we could set a breakpoint for reading the jumping gravity data from the ROM *but* exclude the specific reference used for Mario jumping to see if it breaks somewhere else. Side note - STILL impressed with your Castlevania: SotN video. Holy cow.

@@DisplacedGamers Thank you so much! I'm currently working on my Sinistar video next; really excited to show off what I uncovered.

You could change the value referenced for “no button pressed” falling if you wish. Change six to something else.

it depends but an example would be that the game evaluates the input multiple times when you press one direction acceleration to a certain speed is applied but after that the games reads the other direction and the check that cancels the acceleration ia skipped and you end up accelerating uncontrolably

A lot of controller checks use binary arithmetic to filter out combinations of d-pad and/or button presses as part of their controller conditionals. The combinations tend to work under certain assumptions, and those assumptions are that Up+down and left+right are combinations that should never exist. Of course, even original controllers can have their d-pad plastic wear over a period of time and allow opposite directions to be pressed. Programming under those assumptions *does* make sense for several reasons - including saving ROM space as well as execution time thanks to neglecting the implementation of a base case (equivalent of "else" in a higher level language) in the controller code. This unfortunately means that various side effects occur as code execution will - in my own words - "pinball around" a little bit in a loose structure of logic for some amount of time during the frame or across multiple frames. This may result in game objects being in a broken state during and/or after the illegal input.

The Y-Position is relative to the level instead of the screen. For gravity/YSpeed application, the logic bumps the number up to the next integer value and then later compensates the value using another RAM value for head/feet position within a block.

Oooh. Hmm. That does sound interesting.

Captions seem OK. Maybe clear your cache/cookies?

@@DisplacedGamers RU-vid had it set to something that looked to be invalid. Changing the setting helped, it seems.

The results are better than I could have possibly imagined. 222C-AF6F

@@DisplacedGamers New video or are you just gonna tell us? Haha.

@@briankarcher8338 Maybe my first ever Short?

@@DisplacedGamers Sharts 🤮

Thanks!

Me and a friend messed around with some SF2 Turbo GG codes and somehow got air combos and counters working. That was a fun one, smacking each other a dozen times before we hit the ground.

D12C-AF6F = Gravity 6. Yes. He is still assigned an upward velocity. The gravity value of 6 causes it to "decay" quite fast, though.

If you were to assign a value of 80 or more, though, THAT would prevent Mario from ever leaving the ground. He's given an initial Y-velocity of -80. No idea what that would be in GG values though, since the codes aren't actually hex...

You may want to check to see if the damage dealt is only part of the byte. It is possible some bits are used for other attributes. That said, the idea does sound rather stingy for a system with the SNES' amount of RAM. Not uncommon on the NES, though.

@@DisplacedGamers it does seem like an overly simple calculation, but it's the best I can figure. The different weapons seem to only change the maximum damage when it rolls RNG. Of course it averages out to way more damage, but is a bit unsatisfying. To check if it's only part of the byte, would I want to try messing with the address before or after it? I'm really unfamiliar with how the SNES hardware works, just the basics of the SNES9x cheat search tool.