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A Comprehensive Super Mario Bros. Disassembly

gist.github.com

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Re: A Comprehensive Super Mario Bros. Disassembly

#3

Post by jordigh »

https://gist.github.com/1wErt3r/4048722#file-smbdis-asm-L601...

I think this is where the real gems start. The biggest contribution that SMB had was the "physics engine", to retrofit a modern term. The friction, the jumping, the inertia. If you compare it with the primitive physics in Donkey Kong or Mario Brothers, you can really grasp the groundbreaking novelty that was SMB. You can change direction in mid-air, but not too much. When you run, you skid if you try to run in the opposite direction. The height of your jumps is affected by your running speed.

It's all of these little details combined, barely noticed in tandem, which made the game new and fun.

Re: A Comprehensive Super Mario Bros. Disassembly

#4

Post by tomduncalf »

This seems like a really impressive effort to make sense of all this!

Would the original game have been written in assembly? And if so, would the source have looked similar to this?

Having never touched assembly language (aside from learning some very basic cracking many years ago swapping JE for JNE in the serial check routine, haha), it seems like a true dark art to me, so I’m really curious to know!

Re: A Comprehensive Super Mario Bros. Disassembly

#6

Post by davidscolgan »

jordigh wrote: post #3

https://gist.github.com/1wErt3r/4048722#file-smbdis-asm-L601... I think this is where the real gems start. The biggest contribution that SMB had was the "physics engine", to retrofit a modern term. The friction, the jumping, the inertia. If you compare it with the primitive physics in Donkey Kong or Mario Brothers, you can really grasp the groundbreaking novelty that was SMB. You can change direction in mid-air, but…

I once read that the way SMB was able to pull off the physics engine on such limited hardware was that it used lookup tables for physics instead of actually calculating velocity. My assembly-fu is weak but it looks like your link is to the section that contains all the lookup tables. I think JumpMForceData for example is a series of offsets for each successive frame after you hit the jump button.

https://gist.github.com/1wErt3r/4048722#file-smbdis-asm-L611...

This line shows the calculation that makes use of the JumpMForceData.

Re: A Comprehensive Super Mario Bros. Disassembly

#8

Post by Kelbit »

tomduncalf wrote: post #4

This seems like a really impressive effort to make sense of all this! Would the original game have been written in assembly? And if so, would the source have looked similar to this? Having never touched assembly language (aside from learning some very basic cracking many years ago swapping JE for JNE in the serial check routine, haha), it seems like a true dark art to me, so I’m really curious to know!

Yes, the original game would have been written in 6502 assembly, and probably would have looked something like this. The label names and defines would have been different, since the ones in this file are the interpretation of the person who did the disassembly.

Re: A Comprehensive Super Mario Bros. Disassembly

#9

Post by bluedino »

tomduncalf wrote: post #4

This seems like a really impressive effort to make sense of all this! Would the original game have been written in assembly? And if so, would the source have looked similar to this? Having never touched assembly language (aside from learning some very basic cracking many years ago swapping JE for JNE in the serial check routine, haha), it seems like a true dark art to me, so I’m really curious to know!

Yes, the original NES games were written in assembler. However, the source probably didn't look quite like this. I'd guess the assembler of the time didn't have as many features or things like long label names.

Here's some actual Atari 7800 (a less popular console from the same generation) code that was found on disks in a dumpster when some Atari offices closed. They both use a 6052-based CPU but have very different sound/graphics chips. I'd bet the NES code looked a lot more like this - https://github.com/OpenSourcedGames/Atari-7800

Re: A Comprehensive Super Mario Bros. Disassembly

#10

Post by aquova »

tomduncalf wrote: post #4

This seems like a really impressive effort to make sense of all this! Would the original game have been written in assembly? And if so, would the source have looked similar to this? Having never touched assembly language (aside from learning some very basic cracking many years ago swapping JE for JNE in the serial check routine, haha), it seems like a true dark art to me, so I’m really curious to know!

Yes, all old NES games were written in 6502 assembly (named after the NES's 6502 processor), and even most games into the Super Nintendo and Game Boy days were written using assembly language.

The source would've looked very similar to this, although I can assume the original labels would've been in Japanese. The difficulty in creating a disassembly like this isn't converting the machine code back into assembly, which can be done rather simply, but instead re-adding all the label names, which are lost when the game is built. It's quite the undertaking, and the author must know the complete game back to front.

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