I have experience distributing visual novels, though most were official and unofficial translations of Japanese visual novels where I did technical work (not the actual translation). I won't go into details on that due to NDA through.
First of all, Ren'Py has a hidden limitation in distribution. If you unzip and zip again, odds are that you ruined file attributes and then the mac version won't start and I think linux version too, through I never encountered that personally. I have seen multiple times that amateur VN makers click windows/mac/linux distribution in Ren'Py's project menu and then unzip the file to zip it again as multiple archive for distribution with file size limits for each file. This then results in mac users complaining that it won't start and the creator then usually has no idea they broke anything because it works on their windows computer. The easy fix to this is to create a multi file zip containing the original zip file. Yes it's annoying to add an extra step to unpacking, but it saves a headache later.
The simplest way to distribute is to zip the zip given from Ren'Py and set each file to be max 3.9 GB. This way it won't even cause problems if somebody use outdated software and is still limited to a 4 GB file size. I believe this is distribution approach, which is the least likely to cause problems for the end user.
As for making an upgrade download, I will point out that there exist a solution to this already. It is essentially the same issue as when companies release a VN on a DVD and then provide patches online. Ideally such patches are as small as possible one reason why people might pay extra to get the DVD as opposed to just the download version could be poor internet connection. Alternatively a small download size means less server load. Either way years ago there was one or more commercial interests in finding a solution to this problem.
The approach is to have multiple folders and each folder is packed into a file for distribution. As I recall that's how Ren'Py is by default. Version 13 is then released as it is right now (no change). Then to add the update feature all new graphics are added to a version14 folder. The script then points to version14 when using the new ones while maintaining the old paths for all existing images (and videos etc). If done right, upgrading from version 13 to 14 will then be downloading a new scripts file and version14, hence two files. The user then adds version14 and overwrite scripts and the game will be updated. Repeat for version15.
The obvious benefit of this is much smaller downloads when updating. There are two negative consequences to it through. One is that say there is a movie in version 13, which is remade in version 14. While the old one can be deleted from the full version, people who upgrade will keep the old movie file, which in turn means the installed game is larger when updated than if all is redownloaded. The other issue is that it will fragment the file locations. Say there is a subfolder with Rachel doing (whatever) as a series of background images. A future update replaces one of them to fix a consistency issue, which then means one image from the set is in a different folder than the rest of the set.
Remember this approach was developed to handle small downloads, like fixing script bugs and not to add more chapters. By definition if a VN is released as a DVD then the story is done or you are doing it wrong. I won't say I haven't seen content being added post release, but it's not how it's supposed to work.
There are update creators, which compare the files of two versions and creates a file detailing how to change one to the other. However while that will work fine with unpacked files, I do not believe packed files will benefit from this, particularly not if encrypted or compressed. I do not expect them to work with the files created by Ren'Py or rather it might work, but the patch download might be as big as the zip file itself, completely voiding the point of the patch.
I will strongly recommend doing the multi file zip of a single zip for distribution to keep the file size of each download to something manageable with as low a risk as possible for corrupting anything. The update approach is however something, which I don't know if it's a good idea in this case or not. For all I know it might completely ruin the internal workflow. Still I do believe this is the approach if there is going to be a small update file in the future and since people started talking about it, I felt like mentioning this.
This is a horrible workaround because:
- transferring savegame data will be tricky
- the combined filesize of the downloads will be even bigger because there are many shared files (like the map of the school)
- having the same file in multiple releases is a maintenance nightmare, which is prone to updating one and not the other, which then causes bugs
- it's not a good player experience to have the game quit and then you need to resume by starting what is essentially a different game
- It's not a linear story and a number of events aren't linked to a specific chapter. Should they be included in multiple chapters?
In short I don't see this approach ever being able to work from a technical point of view. Splitting up the game will break a bunch of stuff, which takes ages to fix and transferring data is a nightmare, both in development and for the player.
Sadly since Telltale Games went bankrupt, BTTF the game is no longer for sale. There is no point in searching for it if you haven't bought it already.
