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Hi dear people of TL forums,
A while ago, I started working on Brood War bot development. During this endeavor, I decided to write a book about it - and one of the chapters of this will be dissecting the code of StarCraft itself. This is quite an undertaking, but I'm making progress with it. Don't let the title "Brood War API" fool you, if you're a gamer, you might still find it interesting!
Here are the posts I have so far. I plan to post updates in this forum in the future, as I publish the episodes:
(Last update: 2019-11-14)
Brood War API – The Comprehensive Guide (of time and space)
Brood War API – The Comprehensive Guide – Distances, high ground, and unit behavior
Brood War API – The Comprehensive Guide – Unit movement, and worker behavior
Brood War API – The Comprehensive Guide: Creating buildings, and everything about the creep
Brood War API – The Comprehensive Guide: Buildings, and placement
Brood War API – The Comprehensive Guide: Movement modifiers, and Terran units
Brood War API – The Comprehensive Guide: Terran units continued, and some Zerg ones
Feel free to ask questions, point out mistakes/typos! I have a pretty good plan how I want to proceed with the topics within the book, and I'd like to publish updates at least weekly.
Enjoy!
Sonko
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Nice work! I had a skim through it and even that taught me some things. A question though, what is the deal with detectors and moving? I wasn't aware that moving had any effect on a detector's ability to detect? Or is this just about its "detection region" only being updated every so often, ala sight?
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Northern Ireland26223 Posts
Ah great, been looking for some light reading material!
Joking aside this is pretty cool, look forward to having a proper look later today.
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Thanks for the feedback!
. A question though, what is the deal with detectors and moving? I wasn't aware that moving had any effect on a detector's ability to detect?
I don't really get your question here  Can you maybe quote the part that implies that?
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[quote=Sonko]Detector: If the unit is immobile, it can detect cloaked units within its sight range. If it’ mobile, it’s not constant. Blinded, incomplete, or disabled units cannot detect, and neither do hallucinations.[/quote]
This was the text that I wasn't sure about. "If it's mobile, it's not constant".
I thought that meant moving units versus stopped units, but I'm guessing the distinction is between say, a missile turret and a science vessel? And you just mean that the region detected is not constant for a moving unit?
(which of course makes perfect sense)
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Yes, you're correct Maybe I'll rephrase that to be more clear.
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How did you get the SC source code?
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The short answer is I didn't I use openBW, a decompiled source - see the first article
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Wow this is really interesting stuff... thanks for sharing! The coding is crazy lol
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Hero defiler (Unclean One) also has a different collision box than a regular Defiler.
For presenting tile/subtile grids you should better use screenshots from SCMDraft with walkability flag overlay.
People less versed in the OpenBW code, or coding in general, would probably like it if you would explain variable types and other definitions a bit.
The switching into additional terrain flags (cover, terrain level) also comes a bit sudden. You probably should write a more elaborate introduction to terrain flags first (you brush on all of it a bit, but I don't think it is very comprendable without prior knowledge).
The relationship between walkability and buildability is actually… a bit complicated… (Partially) unwalkable, but buildable tiles have some very interesting and useful effects.
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Very interesting keep up the good work!
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Does APM / speed of hand / latency / ping affect how units work / attack / move or is that all in my head?
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"Does APM / speed of hand / latency / ping affect how units work / attack / move or is that all in my head?"
Latency is something you have to compensate for at some point, if you develop an AI. Other than that, they do, but not in the code
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I know close to nothing about coding but this is super interesting! Thanks for sharing
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You're welcome Also, if you want to get into programming, this is a great project. Many students have walked that path before
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Thanks everyone for the feedback! I corrected a few minor things, and rephrased stuff. I plan to release the next article soon!
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Really enjoyed your series on molesting crabs and such, looking forward to your newest deep dive!
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And the next part is here. It's a little all over the place, I extended and revised some of the earlier parts, and added stuff here. Anyway, it's about movement modifiers, and code behind Terran units.
Read it here!
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Really enjoyed your series on molesting crabs and such, looking forward to your newest deep dive!
Thank you! Hovercrabs cannot be molested enough!
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Netherlands5198 Posts
When I issue attack move command on a group of medics and marines, the medics will act the same as if I ordered the heal move command.
I always assumed it was because heal also has the hotkey a (by default). If I change the attack move hotkey from A to Z and issue attack move via Z Medic/Marine in the same group will make the medics respond the same.
My conclusion is they have coded attack move on medics to work the same as the heal command. Because other non-attacking units receive the attack move command just move instead.
If you select a group of carriers and build interceptors, all carriers will build interceptors. The same way a group of reavers will all build scarabs. Or all tanks will siege, etc.
Can you easily decipher from the code if all these special actions are specifically unique?
I'm basically asking if there is any combination where you can have 2 (or more) different units listen to same assigned hotkey the way medic marine do.
I've tried to set scarab building and interceptors to the same hotkey. In hopes that I can order a group of carriers and reavers to both build interceptors and scarabs respectively, but it doesn't work.
And I've been wondering if it is ever possible to combine 2 commands in one hotkey? For example burrow and siege mode or mael strom and psionic storm? I'm curious but too lazy to test all combinations.
Imagine being able to cast ensare and plague with just 1 click, or storm and mael strom... 
Can you see how the area plague hits is defined in code? Because from my experience it seems like the aoe is slightly skewed to the right of where you click instead of being centered and ever since I wondered if it may be a small number mistake in coding.
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Hi Peeano,
I was considering answering your questions one by one, but truth to be told, all of these are to be covered in later articles, so just stay tuned. If you have some coding background, you can take a look in the source files of openBW here:
https://github.com/OpenBW/openbw/blob/master/bwgame.h
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Wow, what an excellent series of articles. Thank you so much for sharing.
I had no idea that all ranged attacks have a 1/256 miss chance by default!
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Btw you reference an appendix often, is this posted anywhere on the site? I'm assuming it's lifted from the forthcoming book where you do have an appendix, but there's a few things I'd like to check if you already have it up.
Also nitpick about this section:
Second, an addition to the Energy segment of unit abilities:
The starting energy of a unit is the quarter of the maximum energy of the unit type (rounded up), so upgrades affect it. The exception is the Protoss Shield Battery, with the starting energy of 100.
Dark Archon is another exception. They always start with 50 energy even with Argus Talisman researched.
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Hi,
Btw you reference an appendix often, is this posted anywhere on the site? I'm assuming it's lifted from the forthcoming book where you do have an appendix, but there's a few things I'd like to check if you already have it up.
Not yet. What are you curious about? Maybe I can look it up for you. Also, I'm considering adding stat blocks and weapon statistics to the untits' description - a little bit redundant, but maybe it would look good.
Dark Archon energy: Thanks for the find, I will add that!
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This is very interesting:
Particularly because ScmDraft does not implement this correctly yet. Gotta ask SI about it.
Anyway, I looked it up, and the function to calculate distances looks like this in OpenBW:
int xy_length(xy vec) const {
unsigned int x = std::abs(vec.x);
unsigned int y = std::abs(vec.y);
if (x < y) std::swap(x, y);
if (x / 4 < y) x = x - x / 16 + y * 3 / 8 - x / 64 + y * 3 / 256;
return x;
}
It's easy to see how this would give you a dodecagonal structure like depicted above, although I haven't figured out how they came up with this particular approximation yet. Also gotta wonder why they did not just use simple Euclidian distance (I know that square roots are computationally bad, but there is little need to ever calculate and actual distance, only thing of interest is usually to check whether something is within a certain range, which can be done using only squares).
Anyway, this is certainly an interesting piece of code that you should discuss in some detail when you talk about distances.
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(a*a + b*b) costs up to 80 cycles in "ye olden times" (warcraft 2 era)
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Also aren't all these division operations optimizable by using bit shifting?
PS. does anyone know if there's any info about the save game file formats (single or multiplayer) anywhere? I have not found anything on google at all
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so gotta wonder why they did not just use simple Euclidian distance
In uniform grids, that is usually not the best approximation.Generally, the Manhattan distance is considered to be best.
Here is a link that explains the what and why:
http://theory.stanford.edu/~amitp/GameProgramming/Heuristics.html#heuristics-for-grid-maps
Also aren't all these division operations optimizable by using bit shifting?
In the openBW code, there are often bitshifts. But that's a decompiled reverse-engineered version. Functionally identical, but I'm not sure that these things are exactly the same. They probably are, though.
PS. does anyone know if there's any info about the save game file formats (single or multiplayer) anywhere? I have not found anything on google at all
Yeah, surprisingly little information. I'm not there yet.
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Croatia9527 Posts
Awesome! Really cool stuff dude.
One small suggestion: drop "BWAPI" from the name of the articles. Seems like most (all?) of these articles are describing the internals of BW itself and don't have much to do with BWAPI, so it might just cause confusion. If there are some articles that talk about BWAPI, then it'd be good to recognize those as such.
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One small suggestion: drop "BWAPI" from the name of the articles. Seems like most (all?) of these articles are describing the internals of BW itself and don't have much to do with BWAPI, so it might just cause confusion. If there are some articles that talk about BWAPI, then it'd be good to recognize those as such.
In the long run, this is a part of the BWAPI book - this chapter just got a little bit longer than I anticipated
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Croatia9527 Posts
On November 14 2019 18:35 Sonko wrote:Show nested quote +One small suggestion: drop "BWAPI" from the name of the articles. Seems like most (all?) of these articles are describing the internals of BW itself and don't have much to do with BWAPI, so it might just cause confusion. If there are some articles that talk about BWAPI, then it'd be good to recognize those as such. In the long run, this is a part of the BWAPI book - this chapter just got a little bit longer than I anticipated
It might be a good idea to be able to quickly sort BWAPI articles from non-BWAPI articles, so that people who are only interested in BW internals and not so much in BWAPI itself, could quickly find what they're looking for ^^.
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By the way, I lied a lot. Here are some corrections, or rather, clarifications - just as an example
I made these corrections in the article as well. I'm constantly revising, rephrasing, and verifying all of this - not without help, of course.
When upgraded, the Vulture is the fastest unit in the game. - technically, only the unit with the fastest average top speed among the controllable units. Nukes, scarabs, and interceptors are faster, for example.
(Spider mines) After being laid, it is invisible in the ground (like burrowed units)
They actually take some time to become invisible.
Added this section to the spider mine damage section:
"It fires a stationary bullet when 30 distance away from the target, then gets destroyed 9 frames later. Since this is splash damage, this explains why running away from mines can reduce the damage taken. (See Combat and Damage for more details)"
The tank's turret and base are handled as two separate units in the game code, but that has no bearing on gameplay.
That was a blatant lie. Corrected it to:
This allows the turret to face an enemy unit, while the body moves in a different direction. So when stopping and attacking, the unit does not need to change facing, effectively making it a bit more effective at hit and rtun attacks.
Also with Goliaths:
The turret can turn away from the direction of the body, but has a limit of 32 angle units, so in practice this works more like an increased fire arc.
the Valkyrie fires 8 rockets, and cannot move until all of them are fired.
It can, it just cannot be interrupted during this.
Larva timing is further clarfiied to this. (Imagine digging this out)
Each Hatchery has a larva_timer variable, which is set to 37 when a larva is spawned. This gets decreased every 9 frames, but that timer is randomized every 150 frames. So this timer is subject to 2 or 3 randomizations. This means that as long the larva count is never max, larva will spawn every 328-361 frames, otherwise this number will vary between 319-360.
I also added this to the Spore Colony:
Since it’s a building, the detection range is 7 tiles, or 7*32 pixels, which is not the same as the unit’s sight range)
but spore colony does not
It's of course, a matter of how precise I want to be exactly. At some point, it's a pointless exercise, but I feel I'm far from it.
Kudos if you have noticed any of these while reading the article :D
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It might be a good idea to be able to quickly sort BWAPI articles from non-BWAPI articles, so that people who are only interested in BW internals and not so much in BWAPI itself, could quickly find what they're looking for ^^.
Okay, you have a point, I'll add some clarifying label.
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Croatia9527 Posts
Another small suggestion: you should update the original post of this thread to include all of the newer articles as well.
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Another small suggestion: you should update the original post of this thread to include all of the newer articles as well.
Thanks, I wasn't aware I can do that. Added the new articles!
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Belgium6774 Posts
This is AWESOME. Thank you!
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EPT![[image loading]](https://i2.wp.com/user-images.githubusercontent.com/23058097/49927455-8deb9e80-fe83-11e8-936f-3dbf105fbd65.gif?w=625&ssl=1)
![[image loading]](https://i0.wp.com/makingcomputerdothings.com/wp-content/uploads/2019/11/image-1.png?w=323&ssl=1)
