Game Engine White Papers: Commander Keen

https://forgottenbytes.net/commander_keen.html

by mfiguiere • 1 month ago

240 80 1 month ago

evilturnip• 1 month ago

Masters of Doom is a great book on the history of id software, which includes the origins of the development of smooth scrolling by Carmack and Romero, which was groundbreaking at the time on PC.

_the_inflator• 1 month ago

Fun fact for C64 guys:

The underlying mechanics of Carmack's technique is very similar to the full screen smooth scrolling effect on C64 at any speed and distance. It is nowadays referred to as DMA delay.

ELIF: You trick the CPU to display screen data at a different starting point than as designed by the hardware. This is tricky and need to be executed cycle exact.

Here is the explanation in detail together with all major top notch effects. The article is a legend and kind of the bible of doing the most sophisticated effects on C64. Some effects have since then even more and better explained and exploited due to cross platform development possibilities and better tooling, but understanding all mechanics here is a necessity to play a role in the Champions League of C64 demos, besides and also being able to implement the techniques mentioned here: https://www.zimmers.net/cbmpics/cbm/c64/vic-ii.txt

lazystar• 1 month ago

ELIF: You trick the CPU to display screen data at a different starting point than as designed by the hardware. This is tricky and need to be executed cycle exact.

heh, is there a new meaning for ELIF? im not sure that there are many 5 year olds who would understand that ;-)

bonzini• 1 month ago

To clarify, it does not need to be executed cycle exact on the IBM PC, only on the C64.

hbn2• 1 month ago

It should be noted that John Romero released his own book, Doom Guy, a few years ago which contradicts some of the accounts in Masters of Doom. MoD is probably the more thrilling read and I enjoyed both books, but some of the stories need to be taken with a grain of salt.

I also think Doom Guy is worth a read because it gives a lot more insight into what happened at Ion Storm and how the Daikatana project fell apart. And some important context about the infamous "John Romero's about to make you his bitch" ad (mainly that he really didn't want to publish it at all). But I digress.

vunderba2• 1 month ago

Yeah that's confirmed in Masters of Doom as well - sounds like Romero was a bit hesitant about it but Mike Wilson, the marketing guy, pushed him into it.

memsom• 1 month ago

I would recommend the audiobook - John Romero actually reads it so it seems a lot more personal.

I did feel that Romero skipped a load of stuff, at least int he audio version. There was no real mention of Stevie Case, just one passing name check. That was really odd. I was expecting him to at least mention her.

I've also both read and listened to Masters of Doom (read by Wil Wheaton no less) and it is a great book too. The audio version is really good.

rendaw• 1 month ago

I've been following the Japanese early gaming scene, which had a lot of parallels to the west. They had NEC PCs running DOS, and there were a lot of games for the systems. Some of them had smooth scrolling. Did they come later? Did they copy ID Software's approach?

instagraham• 1 month ago

One thing I was sus from the book and which this post didn't clarify for me was whether Carmack truly invented side scrolling for the PC. He claimed to have done so, and even pitched it to Nintendo for a Mario port that never took off.

Also, the idea that it hadn't been done yet by 1990, when consoles were well in the game, suggests the PC market was behind popular gaming in a big way.

WorldMaker• 1 month ago

The consoles at the time had dedicated sprite video RAM and hardware and dedicated hardware instructions for background scrolling. The NES for instance had up to 64 sprites (independently moving 16x16 or 32x32 pixel images) supporting up to 8 of those sprites per scanline. The NES background layer was a relatively simple tile map that supported smooth scrolling. All of which was managed by a dedicated hardware Picture Processing Unit [1].

PCs were designed to be general hardware and it didn't seem to make sense to create a generic "PPU" for the PC, so instead game engines at the time (and many game engines to this day) had to emulate one entirely in software. The video RAM of EGA and VGA is just one big blob of pixels, or perhaps two if your system supported double-buffering. At the hardware level it doesn't have concepts like sprites or scrolling backgrounds.

Carmack was one of the first (if not the first; Commander Keen was also among the first commercially successful attempts) to get a software "PPU" renderer on the PC working reliably in real time. Another notable achievement for side scrollers on the PC in that era was Cliff Bleszinski managing to software render the parallax effects similar to Sega's "Blast processor" PPU (notable for "gotta go fast" Sonic games) for Jazz Jackrabbit (in 1994).

It has sort of long been the arc of PC development of eventually doing entirely in software what consoles and arcades were doing with dedicated and/or one-off hardware. (Right up until about the invention of the modern GPU when suddenly the PC was leading graphics hardware in a different way.)

[1] https://www.nesdev.org/wiki/PPU

LarsDu884• 1 month ago

Someone ping Fabien Sanglard! Looks so much like his site!

bel82• 1 month ago

And his site looks like another thousand, as I'm sure he knows.

We consume his site for the content, not for the minimalistic design that exist since the inception of the universe.

sasas8• 1 month ago

It appears the author is leveraging Fabien's branding by copying not only the style of post but more importantly the formatting and style of Fabien's books. Even structurally the book appears quite similar.

If you didn't double check the author while skimming this Keen book, you may well be mistaken that it was written by Fabien.

I took a quick skim of the content, it looks great - tempted to purchase a copy to support the author for their efforts (and have it sit on the bookshelf next to two other very similar looking books...) but need to sit on this for a while.

Maybe I'm overthinking this. Would like to hear Fabien's take on the situation.

[EDIT] It looks that the Keen book author copied and pasted direct sections[1] out of Fabien's book's TeX[2].

[EDIT] The git commit history has comments that indicate that Fabien reviewed the book, e.g. "updated all chapters after feedback Fabien" and "Proofread Fabien Sanglard en hardcopy review", so perhaps this is all sanctioned.

[1] https://github.com/bsmits74/Keen_White_Papers/blob/master/sr...

[2] https://github.com/fabiensanglard/gebbdoom/blob/master/src/b...

charlietran• 1 month ago

Author's note from the book:

"...I discovered Fabien Sanglard’s website and began reading his Game Engine Black Books on Wolfenstein 3D and Doom. Inspired by those works, I wondered whether I could do something similar for Commander Keen: open up the source code, explore the files, and piece together a picture of the overall architecture and the clever tricks used. The style, dimensions, and structure of this book are intentionally similar to Fabien’s Game Engine Black Books, as an homage to those masterpieces. To give it a personal twist, I inverted the title and cover to white."

fabiensanglard5• 1 month ago

To give it a personal twist, I inverted the title and cover to white.

That is a great idea.

_jackdk_• 1 month ago

I think it's a really cool homage, but that the site could be a little clearer that it's not Fabien's work. When I first clicked through and saw a different name, I was hopeful that someone had started a publishing house dedicated to high-quality dissections of classic games.

ndiddy• 1 month ago

Wow I assumed it was one of his books before I saw your comment. Thanks for pointing that out!

LarsDu884• 1 month ago

Lovely book. Skimming through it. One thing that might help contextualize it is a brief discussion of the how contemporary hardware like the SNES rendered sprites so efficiently compared to the PC hardware at the time. It's not obvious to modern readers why a PC with significantly more powerful compute capabilities would struggle to keep up with significantly slower Nintendo hardware at the time for sprite rendering.

mrob2• 1 month ago

It's not obvious to modern readers why a PC with significantly more powerful compute capabilities would struggle to keep up with significantly slower Nintendo hardware at the time for sprite rendering.

To put it briefly, 4th generation and earlier games consoles saved on expensive RAM by not having frame buffers [0]. The CPU wrote a description of how to construct the scene using tiles and sprites to a smaller video ram, then dedicated video hardware converted this to the video signal one line at a time. The whole frame gets rendered from scratch every video refresh, so there's no need for tricks like Commander Keen's adaptive tile refresh. Scrolling at 60 fps (or 50 fps for PAL hardware) is as cheap as changing a single value in video memory. It's like the famous "racing the beam" of the Atari 2600, except less flexible and done by dedicated hardware so you don't tie up the CPU.

On the PC, the CPU writes the actual graphics to a frame buffer, then the graphics card outputs the contents of the frame buffer as the video signal. The naive approach to scrolling requires rewriting the entire frame buffer, so tricks to avoid redundant writes are highly beneficial.

[0] Except for the Atari Lynx, which was a portable system with a screen resolution of only 160×102. I can't think of any other exceptions, but maybe there are more.

wk_end3• 1 month ago

I get what you're saying, but the comparison to "racing the beam" is maybe a little misleading, because the point is that you aren't "racing" the beam. Rather, the system is operating in perfect lockstep with the beam. From the software perspective, you set the scene up and then sit back while it draws. And then in the abstract and from the hardware's perspective it's not even one line at a time, it's one dot at a time.

matheusmoreira• 1 month ago

These videos do an excellent job at explaining how the SNES works:

https://www.youtube.com/playlist?list=PLHQ0utQyFw5KCcj1ljIhE...

rtpg• 1 month ago

the Gameboy, not the SNES, but this talk is very very good at going in detail about a bunch of internals. The graphics stuff is 29 minutes in but I love the whole video. Very much a high level guide to building a "retro-y" fantasy console for people into that stuff

https://youtu.be/HyzD8pNlpwI?t=1759

fredoralive• 1 month ago

It's basically a case of hardware acceleration. Most games consoles and fancier micros have some of dedicated graphics chip that handles the heavy lifting of generating graphics. So for basic game graphics the CPU largely acts as a manager adjusting things like tilemaps and their viewport offsets, and sprite locations (possibly updating things several times mid frame, for fancier effects). The exact setup differs between systems, tilemaps and spites like the SNES is common, though you also have setups with some sort of framebuffer and a Blitter to speed up drawing to it instead.

A traditional IBM PC has a "dumb" framebuffer, where everything is done by the PC. Simply scrolling the background by 1 pixel basically means redrawing a lot of the screen, and you have to keep track of what graphics behind sprite would need to be redrawn after they move etc. As a bonus, on early consumer level 386 and 486 machines you have a mighty processor, but the graphics card is often still on a 16 bit 8MHz(ish) ISA bus. The PC does have an advantage that it's more flexible, so stuff like 3D was easier to do than on a tile-and-sprite setup (especially once we had stuff like VESA and PCI).

woutersf• 1 month ago

If you want to play it you can do that here: https://www.playdosgames.com/play/commander-keen-4

snodes• 1 month ago

It's also on Steam: https://store.steampowered.com/app/9180/Commander_Keen/

basisword• 1 month ago

I had no idea you could still get it. This brings back memories! My first and favourite game as a kid. I'd get home from school, boot up the DOS machine and type 'keen.exe' to start it up.

pan69• 1 month ago

Great write up. Reminds me of Cosmodoc, which is similar source but analyzes Cosmo’s Cosmic Adventure instead of Commander Keen.

https://cosmodoc.org

ChrisArchitect• 1 month ago

Of related interest:

Reconstructed Commander Keen 1-3 Source Code

https://pckf.com/viewtopic.php?t=18248 (https://news.ycombinator.com/item?id=46321982)

nnnnico2• 1 month ago

this looks like a copy of fabien's site, plus the topic is very related and likely trampolining on his brand :/

mrandish• 1 month ago

Fabien's site is an invaluable resource, but I think I've read it all over the years and he one has post specifically on Commander Keen, and that's focused on just the adaptive tile refresh (https://fabiensanglard.net/ega/). This book is 211 pages on the entire game.

On the first page this author credits Fabian's excellent analysis of Doom and Wolfenstein as the inspiration to attempt the same for Commander Keen.

"Fast forward to 2021, I discovered Fabien Sanglard’s website and began reading his Game Engine Black Books on Wolfenstein 3D and Doom. Inspired by those works, I wondered whether I could do something similar for Commander Keen: open up the source code, ex plore the files, and piece together a picture of the overall architecture and the clever tricks used. The style, dimensions, and structure of this book are intentionally similar to Fabien’s Game Engine Black Books, as an homage to those masterpieces."

Just skimming so far, but this book looks like a valuable contribution to the genre of retro game code analysis. Obviously, it will build on the work of others who've done adjacent research. In a page 87 footnote the author refers readers to Fabien's site for detailed instructions on installing a DOSBox and Borland C++ dev environment.

bel82• 1 month ago

First, shallow dismissals are against HN guidelines, for a good reason.

And I fail to make the connection. This content-heavy but minimal design is not unique.

Text inside a centered element, text-heavy but also packed with images, exists from the times of formatinng websites with `<table>` tags in DreamWeaver or Microsoft Frontpage 98.

If you're talking about the highly detailed article, can we not gatekeep this? I want more of that on the internet, not less.

lelandfe3• 1 month ago

57 lines of CSS and the only distinguishing characteristic, the use of Deja Vu Sans Mono, isn't present.

This is trampolining on his "brand" as much as my text editor is

sasas8• 1 month ago

The book's source has verbatim copy and pasted TeX ripped from Fabien's books which was licensed under GPL.

dang• 1 month ago

I can understand the feeling of loyalty to a widely admired figure (and deservedly so!) but this isn't a great way to respond to someone else's work. Unless there's some evidence of ill intent, why not just classify it as an homage?

"Please don't post shallow dismissals, especially of other people's work. A good critical comment teaches us something."

"Please respond to the strongest plausible interpretation of what someone says, not a weaker one that's easier to criticize. Assume good faith."

https://news.ycombinator.com/newsguidelines.html

nnnnico2• 1 month ago

totally, I wrongly assummed ill intent as I thought it was fabiens work for a good while and then came back here frustrated

BigTTYGothGF• 1 month ago

From the preface: > Fast forward to 2021, I discovered Fabien Sanglard’s website and began reading his Game Engine Black Books on Wolfenstein 3D and Doom. Inspired by those works, I wondered whether I could do something similar for Commander Keen: open up the source code, explore the files, and piece together a picture of the overall architecture and the clever tricks used. The style, dimensions, and structure of this book are intentionally similar to Fabien’s Game Engine Black Books, as an homage to those masterpieces. To give it a personal twist, I inverted the title and cover to white.

wk_end3• 1 month ago

Yeesh, until I saw your comment I thought this was Fabien. I'm sure it's not intentional but this goes beyond "homage" and into "deceptive". The replies to this claiming to not see what the issue is are inexplicable to me.

The work on the book itself looks fantastic, so it's a shame about the site design.

sasas8• 1 month ago

It's often helpful not to immediately assume bad faith without further enquiry. It appears that Fabien had reviewed the book beforehand and he has reposted John Carmack's tweet[1] linking the book.

[1] https://x.com/ID_AA_Carmack/status/2066577536339923091

ForHackernews• 1 month ago

Another game from the same era: https://cosmodoc.org/

doctorpangloss2• 1 month ago

Have LLMs made all arcana about games engineering meaningless?

LarsDu884• 1 month ago

Definitely not. If anything this arcana is what feeds the llms not the other way around.

Imagine if you replaced "games engineering" with "political history" or "nuclear physics"

alberto-m• 1 month ago

Eh, it's not so clear cut. LLMs have definitely killed a lot of fun in reverse engineering old games by making it trivial to solve riddles that in the past would have been interesting problems to work on.

But the field still offers many mysteries that need human brains to be solved.

Whether LLMs are a net positive here depends if one is result-oriented (e.g. wants to rewrite an old game in a modern language) or process-oriented (is there for the investigation work and the intellectual challenges).

bluedino• 1 month ago

Would love to hear about the other Apogee and Epic games, like Epic Pinball, Tyrain, Halloween Harry, Jill of the Jungle, Duke Nukem...

to11mtm2• 1 month ago

Tyrain

... Well, we do at least have OpenTyrian... (Edited to add; And OpenTyrian2000)

Epic Pinball

Best I can find for Epic Pinball is an old thread on Pinball Fantasies [0] but I think it almost counts cause there was shared dev work between the two...

Halloween Harry

TBH that one would be fairly interesting, especially compared to Duke Nukem 2 (Part of me thinks they might be similar/same engine)

Jill of the Jungle

That one honestly WOULD be a fun one to look at... Best I can find is Xargon [1] but part of me always got a vibe that Xargon was some semi-upgraded Jill engine...

Duke Nukem

TBH Duke Nukem '1' would not be that exciting to me. AFAIR it's mostly an adapted CK1-3 engine, letter-boxed with status window to make it easier to calc the redraw.

Duke Nukem 2, is far more interesting since it's a different, more powerful engine (VGA, digital audio support, but AFAIR only required a 286).

[0] https://news.ycombinator.com/item?id=28667945

[1] https://github.com/dos-games/vanilla-xargon

kridsdale1• 1 month ago

IIRC (from being a kid) Harry was 256 color and DN2 wasn’t quite. Also it felt like it had much better frame rate. But I’m sure that could be engine evolution too. Interesting, I hadn’t ever thought of the connection before.

Though the “hot babes stuck in alien pods” from Harry showed up as a central plot point in DN3D.

vunderba2• 1 month ago

I also think the story of Duke Nukem 3D (1996) and the development of the BUILD engine by Ken Silverman would also be a really interesting technical read.

jzelinskie• 1 month ago

Sorry for the "asking for more"-style comment, but it would be amazing if this came in epub and not just PDF.

Waterluvian• 1 month ago

Given its open source in latex format, it should be pretty easy to render it in any format that isn’t asking for significant decision-making on how to structure and format it.

Ie. Rendering to PDF or HTML would be pretty straightforward. Rendering to video, audio, or as a chocolate bar would require more authorship. Would epub be much more work?

turpentine• 1 month ago

It's a shame that the author both erased their own writing style using ChatGPT, and wholesale copied sections of the content from another author.

https://news.ycombinator.com/item?id=48550425

torh• 1 month ago

It looks like a complete rip-off. Both the design of the website and the book cover.

ChrisRR• 1 month ago

I was almost tricked into thinking this was a new Fabien Sanglard book and got excited

97-109-107• 1 month ago

[I Am Error: The Nintendo Family Computer / Entertainment System Platform | Books Gateway | MIT Press](https://direct.mit.edu/books/monograph/4054/I-Am-ErrorThe-Ni...)

Game Engine White Papers: Commander Keen

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