Doc: rewrite patch section (#336)

this gets rid of a lot of information that is not required
and somewhat adds best practice to it

docs/adding games.md

@@ -190,52 +190,43 @@ This is a good way to get any project you're working on sued out from under you.
 The right way to distribute modified versions of a game's binaries, assuming that the licensing terms do not allow you
 to copy them wholesale, is as patches. 
 
-There are many patch formats, which I'll cover in brief. The common theme is that you can’t distribute anything that wasn't
+There are many patch formats, which I'll cover in brief. The common theme is that you can’t distribute anything that
-made by you. Patches are files that describe how your modified file differs from the original one, thus avoiding the
+wasn't made by you. Patches are files that describe how your modified file differs from the original one, thus avoiding
-issue of distributing someone else’s original work.
+the issue of distributing someone else’s original work.
 
 Users who have a copy of the game just need to apply the patch, and those who don’t are unable to play.  
 
-### IPS Patches
+### Patches
-This is an extremely simple, early patch format, but is limited to games of about 16 Megabytes in size or less.
-You will often find IPS patches being used to distribute mods for old video game ROMs.
-IPS patches are a delta patch format, which means they act only as a simple list of alterations that need to be made to
-an original file in order to produce a new one.
 
-Archipelago may use pre-made IPS patches to apply specific changes to a game, but will not create IPS patches as a means
+#### IPS
-of distributing game modifications. Although IPS patches can be applied quickly, creating them is quite slow, so using
+IPS patches are a simple list of chunks to replace in the original to generate the output. It is not possible to encode
-them for distributing randomized games is not current practice. 
+moving of a chunk, so they may inadvertently contain copyrighted material and should be avoided unless you know it's
+fine.
 
-However, due to the format's simplicity, even patch files of this type can unintentionally include copyrighted data.
+#### UPS, BPS, VCDIFF (xdelta), bsdiff
-This is because IPS patches don't have a good way to shift existing data in a file, and thus if data has to be moved
+Other patch formats generate the difference between two streams (delta patches) with varying complexity. This way it is
-forward x number of bytes, which might be necessary for data insertion, the patch will simply include a copy of the
+possible to insert bytes or move chunks without including any original data. Bsdiff is highly optimized and includes
-shifted bytes after the inserted ones. 
+compression, so this format is used by APBP.
-Increasing and decreasing file size is also not a universally supported operation, due to the patch format's age.  
 
-### BPS Patches
+Only a bsdiff module is integrated into AP. If the final patch requires or is based on any other patch, convert them to
-BPS is the younger cousin of the IPS patch. 
+bsdiff or APBP before adding it to the AP source code as "basepatch.bsdiff4" or "basepatch.apbp".
 
-More flexible and theoretically future-proofed for any file size, BPS patches are based on the idea of linear patching.
+#### APBP Archipelago Binary Patch
-Unlike IPS patches, which use a system called delta patching, linear patches act as a series of steps for creating a
+Starting with version 4 of the APBP format, this is a ZIP file containing metadata in `archipelago.json` and additional
-modified file from scratch through a combination of original data and patch data, which is appended onto the end of the
+files required by the game / patching process. For ROM-based games the ZIP will include a `delta.bsdiff4` which is the
-modified game file as the patch progresses.
+bsdiff between the original and the randomized ROM.
 
-This means that some operations, like inserting data into the middle of a file instead of simply overwriting it,
+To make using APBP easy, they can be generated by inheriting from `Patch.APDeltaPatch`.
-are much easier to do.
-However, like IPS, it isn't a format well suited to randomizers, due to the asymmetric costs of creating and applying
-BPS patches.  
-  
-### Xdelta Patches
-Xdelta is the true successor to IPS, featuring better optimization and verification, and manages to transcend many of
-the limitations of IPS. However, Xdelta patches are particularly expensive to create.  
-  
-### bsdiff  
-bsdiff is the current format adopted by Archipelago for creating and distributing patches.
-It is much faster to create patches of this variety, which is why it sees use in this application.
 
 ### Mod files
 Games which support modding will usually just let you drag and drop the mod’s files into a folder somewhere.
 Mod files come in many forms, but the rules about not distributing other people's content remain the same.
+They can either be generic and modify the game using a seed or `slot_data` from the AP websocket, or they can be
+generated per seed.
+
+If the mod is generated by AP and is installed from a ZIP file, it may be possible to include APBP metadata for easy
+integration into the Webhost by inheriting from `Patch.APContainer`.
+
 
 ## Archipelago Integration
 Integrating a randomizer into Archipelago involves a few steps.