Fixing a bug / patching a game without breaking saves

[Rosstin]

So, the worst happened. Someone find a bug deep in our game, in the version we released on Steam. Is there a way we can update the build and fix it without breaking saves?

The worst part is that I have no idea how the Renpy save system works. Does it work by line number? If I alter the script to correct a spelling error will that break saves?

[Zetsubou]

Fix it and try?
ie. Create a save at a place likely to be affected, fix the bug, then try to load it.

It depends totally on your code how easy it is, but Renpy seems pretty good at this.
Spelling changes, adding lines of text, even adding menu choices works okay, as long as the flow remains the same.
But moving existing text into a new label, or changing the logic of a scene, or deleting content may cause a break.

[xela]

Fix it and try?

That's excellent advice

Otherwise almost any change shouldn't break the saves, but if you add new properties to an object (for example), you may have to mess with label start in order to inject it to all objects which had their state saved. It depends on the case but your options are really, really wide here as Ren'Py's saving system is very flexible.

[Vaendryl]

in my experience things will usually be okay though changing label names and removing lines can get problematic.

Particularly if you use a lot of python stuff (your own classes etc) it may be a good idea to use the 'after_load' label which can fix/update some stuff before a save finishes loading and things start being drawn on screen.

[PyTom]

it really depends on the change - if you can explain what change you made, we can give you advice on what the right way to maintain save compatibility is.

[neowired]

I would say, If you change a misspelled variable which is crashing the game when the script gets to it because it doesn't exist, that will not break your saves.
If you change an existing variable into one with a different name and call it, you will have the save call an undefined variable, and that will crash.
If all you are doing is changing some text in the dialogue then there should be no issues.

The saves break if your game tries to read from the saved game a variable which doesn't exist in the saved game.

[Rosstin]

In this case, we had an undeclared variable crashing the game when it got to that line, and so we added a line declaring that to our points.rpy file (where we declare all our variables.)

I was hoping for some documentation in-general about how it works-- do saves work by line number? A combination of label and line number?

What we did ultimately was update it: the crasher was on a specific path at the end, only one person had gotten there, and only 20 people had downloaded the game at that point, so there weren't a ton of nightmare scenarios for us. But in case this happens in the future (I don't think it will but you never know), I'd like to know what I can and can't safely do.

[xela]

In this case, we had an undeclared variable crashing the game when it got to that line

Prolly the best case scenario, you are very likely to fix it by adding any random file with:

Code: Select all

default var_name = proper_value

and it should be fixed.

[Rosstin]

In this case, we had an undeclared variable crashing the game when it got to that line

Prolly the best case scenario, you are very likely to fix it by adding any random file with:

Code: Select all

default var_name = proper_value

and it should be fixed.

Yeah, that's what we did.