File Stream Writing - Suggestions

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[kbandressen]

Damon suggested I work on a way to do file output so mods can store save data and have more flexible persistence so I think I'll start on that (once I've got Visual Studio all set up again).  So while I do that and before I start coding it, I want to know what suggestions people have.

One thing I would want is a way to encrypt data so players can't just open their save file up in notepad and edit it so they unlock everything.  At first, though, I 'll probably just try to get a basic system (pretty much the complement to the file input system we have now) working.

Any suggestions/ideas would be welcomed!

[Damon Caskey]

My thinking was to add in "set" versions of the getfilestreamline() and getfilestreamargument() functions that simply overwrite that portion of the file stream data.

Then perhaps a third command for appending additional lines to the file stream, or automatically appending a line if the line argument of  proposed setfilestreamline() is out of scope (in which case, it should probably return some value so we can verify).

Lastly a save command with path parameter that creates a new file or overwrites if {path} already exists and dumps the relevant file stream to it. You obviously don't want to be writing directly to the text file any more then you want to be reading from it.

I think those additions would be more then sufficient. Let the modder worry about manipulation and verifying what goes in and out. If you add encryption, maybe include a byte parameter in the save command to save with or without it. SX and I had talked about that very thing before (text hacking to get the goodies) and encryption is a great idea, but there are times when a modder might want to intentionally leave it open (among other things, debugging comes to mind).

DC

*Edit:* Something else very important, albeit not directly related to file streams. We need a flag to disable OpenBOR's built in game save feature, and make sure the player has no way to re enable it without hacking the mod. Otherwise it will be a major nuisance to work around and completely destroy any kind of RPG style consistency a modder might be going for.

[Bloodbane]

but there are times when a modder might want to intentionally leave it open (among other things, debugging comes to mind).

 Agreed. While still WIP, let's leave it uncrypted so modders could be sure that the texts are written properly.

[Damon Caskey]

I forgot something very important. See my post above.

DC

[kbandressen]

Yeah, encryption would definitely be an optional thing.  Aside from debugging, there's all sorts of uses for making text files like writing a report with the player's statistics once the game's done so they can see how they did.

And I definitely agree on being able to disable the default engine save code.  It'd be a much nicer solution than having to rig up some kind of levelscript to bypass the engine's load function and start the player in the right place.

[SX]

Unless I'm mistaken and way off.....

I would think we should probably focus on redesigning the save system.  Instead of saving at the beginning of each level we need to save a snapshot of the engine instead.  Kind of how the movie system works at the moment.

Basically scan through all enities and their properties and dump it.  This would also guaranty any script overrides as well to the enties, levels and so on.

We won't be storing the data, just the references to the data.

[Damon Caskey]

SX and basteaud,

Yeah, both of these are pretty far off.

@SX: Our current save system is fine for what it does. What we want to do though is have fully controllable persistent variables, and that's a different thing entirely. We aren't trying to reinvent the wheel for saving games.

Currently global vars are saved automatically along with saved games, but this just makes a mess more then anything else. It's almost too tedious to bother with for scripting of RPG features, and its very presence means you have to write in extra checks just to make sure a past game doesn't break your scripts.

What writing to text will do is allow seamless and elegant addition of thing like level ups, stat increases, unlockables, and so on without needing the save feature at all. You could make some awesome action RPGs (or even a plain ole RPG if that's your thing). It's essentially giving OpenBOR its own little database system, and how cool will that be?

The only modification the current save feature needs for this to happen is an "off" switch to keep it from getting in the way.

@basteaud: Sorry friend, but your post pretty much has nothing to do with anything here, and I'm removing it to keep this thread on topic. You are welcome to post it as a request elsewhere.

DC

[kbandressen]

OK, I've got Visual Studio all happy once again so I'll give this a try pretty shortly.  It shouldn't be too hard as I've got the logfile code to look at as an example of how to do stuff like this cross-platform.  Though from what I'm seeing it doesn't look like there's any way to do this Dreamcast, correct?

[SX]

@KB,
You should be able to now.... if someone spends the time at looking at VMU support since its supported in KOS.

[Plombo]

I don't have any ideas or suggestions at the moment, but I can say that this feature will be very, very useful.

[kbandressen]

Had some time to think about this at work today and here's some things I realized.

One pleasant coincidence I realized regarding encryption: with even just a simple encryption scheme where one modder-specified key encodes and decodes the data, it will be as secure as the SecurePak code if the mod is released in that format.  Since everything in the mod is encrypted by that system, the key will be encrypted as well.

And for encryption in regular mods, I think just encrypting things with a modder-specified key would be enough as well.  Players wanting to hack save data would have to open up the mod, find where in the mod's scripts the key is specified, then use some kind of program to decrypt the save data.  A lot of work, and that's not all.

Crafty modders could easily set up a verification system in their save data that would make it a complete pain to hack.  Like when writing data, add up all the numbers that are stored and store their sum (or a permutation of it if you're feeling really evil) as some unobtrusive value as well.  Then sometime after loading, check to see if everything still matches up and if it doesn't, randomly do evil things like kill the player, give enemies ridiculous amounts of health, or spawn Rickroll cutscene entities. 

Also, one little addition that'll have to be made for this to be useful is to make the file stream input code able to access files outside the pak as that's where anything that gets written by the new functions will have to be.  So I'll probably just add a flag to the existing stuff that defaults to using the path specified inside the pak with the option to use it for stuff in the saves directory too.

And it's good to know that Dreamcast will potentially be able to use this as well, though I have no clue about how KOS works.  Hopefully, once I get the functions done it'll be an easy matter for either someone to port them or for me to figure out the VMU code.

[kbandressen]

Okay, I've done some experimentation/work on this and here's how things are looking to turn out.  So far it's looking pretty good.  I've opened up a filestream with a file from within the pak, appended stuff to it, and then used savefilestream to save it in the saves directory with no corruption.

createfilestream() - makes a new blank filestream that can be added to, returns filestream index

openfilestream("filepath", int x) - loads the file at filepath into a new filestream, returns filestream index
- x = 0 (default): loads file from inside the pak (or base directory if running the mod as a data folder)
- x = 1: loads file from Saves directory

savefilestream(int filestreamindex, "filepath") - saves the specified filestream at Saves\PAKNAME\filepath

I'm thinking that the best way to do file writing would be to have each mod only be able write files in a unique subdirectory of Saves (based on its pak's name).  This way, no mod can overwrite other mods' save data.  I can just imagine some wit making a virus-like mod that systematically goes through replacing each save file with garbage.

File reading is a different matter though.  Mods should be able to access any other mod's save data for reading, allowing for connectivity from a mod to its sequel like retaining a character customization or remembering choices made.

And I'm currently working on this function:

filestreamappend(int filestreamindex, scriptvar, 0/1/2) - adds scriptvar to the end of the specified filestream
- 0 (default): for writing commands, creates a new line before writing
- 1: for writing arguments, adds a space before writing

There's definitely more that can be added after these functions, but once these are done, everything that's needed to store custom save data will be present.  We can work on making it fancy after that.

[kbandressen]

OK, I've got an initial release all done now.  Go play around with it and see what you think!

http://lavalit.com/index.php/topic,4252.msg64733.html#msg64733

[basteaud]

I m trying to create a savegame function.

When i use filestreamappend, here is what i get :

Filename for filestreamappend must be a string.
Script function 'filestreamappend' returned an exception, check the manual for details.

You said we have to use the index of the file, not the name. Is that an error from me or from the function ?


Here is my temporary function :

//-----------------------------------------------------------------------------------
//Save a game
//-----------------------------------------------------------------------------------
void savegame(int gamei){
   void newsavegamefile=createfilestream();
   void oldsavegamefile=getglobalvar("savegamefile");
   void type;
   void variable;
   void variablevaluenewgamei;
   void variablevalueoldi;
   int i;
   
   setfilestreamposition(newsavegamefile, 0);   
   setfilestreamposition(oldsavegamefile, 0);   
   
   do{
      variable = getfilestreamargument(oldsavegamefile, 0, "string");
      type = getfilestreamargument(oldsavegamefile, 1, "string");
      variablevaluenewgamei=getglobalvar(variable);
      filestreamappend(newsavegamefile, variable, 0);
      filestreamappend(newsavegamefile, type, 1);      
      
      for (i=1,i<=7,i++){
         variablevalueoldi=getfilestreamargument(oldsavegamefile, i, type);

         if (i==gamei){
         filestreamappend(newsavegamefile, variablevaluenewgamei, 1);   
         }else{
         filestreamappend(newsavegamefile, variablevalueoldi, 1);   
         }
      }
      filestreamnextline(oldsavegamefile);
   }while (variable != "End");   
   savefilestream(newsavegamefile, "data/savegames/savegames.txt");
   free(oldsavegamefile);
   setglobalvar("savegamefile",newsavegamefile);

}

Savegamefile is organized like a table, with globalvars i want to save/load as lines, and savegame number as columns (7 savegame slots).

globalvar int defaultvalue savegame1 savegame2 savegame3 savegame4 savegame5 savegame6
level1 int 1 1 2 3 4 5 6
level2 int 1 1 2 3 4 5 6
level3 int 1 1 2 3 4 5 6
level4 int 1 1 2 3 4 5 6
skill101 int 0 0 0 0 0 0 0
skill102 int 0 0 0 0 0 0 0
End 1

Savegame function opens existing savegamefile, reads each line completely, and copies each argument to the newsavegamefile (each argument, except for one column, that will be replaced by current globalvar values.)

My load game function is pretty similar :

//-----------------------------------------------------------------------------------
//load a game
//-----------------------------------------------------------------------------------
void loadgame(int gamei){
   int i;
   void savegamefile = getglobalvar("savegamefile");
   void type;
   void variable;
   void variablevalue;
      
   setfilestreamposition(savegamefile, 0);
    do{                              
            filestreamnextline(savegamefile);
            variable = getfilestreamargument(savegamefile, 0, "string");
            type = getfilestreamargument(savegamefile, 1, "string");
            variablevalue = getfilestreamargument(savegamefile, gamei+1, type);
            if(variablevalue!="empty"){
         setglobalvar(variable,variablevalue);
            }
     }while (variable != "End");
      
}

Can you help me correcting savegame function?

EDIT : i found a solution :

Here is the new code :

//-----------------------------------------------------------------------------------
//load a game
//-----------------------------------------------------------------------------------
void loadgame(int gamei){
   int i;
   void savegamefile = getglobalvar("savegamefile");
   void type;
   void variable;
   void variablevalue;
      
   setfilestreamposition(savegamefile, 0);
    do{                               
            filestreamnextline(savegamefile);
            variable = getfilestreamargument(savegamefile, 0, "string");
            type = getfilestreamargument(savegamefile, 1, "string");
            variablevalue = getfilestreamargument(savegamefile, gamei+1, type);
            if(variablevalue!="empty"){
         setglobalvar(variable,variablevalue);
            }
     }while (variable != "End");
       
}

//-----------------------------------------------------------------------------------
//Save a game
//-----------------------------------------------------------------------------------
void savegame(int gamei){
   void newsavegamefile=createfilestream();
   void oldsavegamefile=getglobalvar("savegamefile");
   void type;
   void variable;
   void variablevaluenewgamei;
   void variablevalueoldi;
   int i;
   
   setfilestreamposition(newsavegamefile, 0);   
   setfilestreamposition(oldsavegamefile, 0);   
   filestreamnextline(oldsavegamefile);
   do{
      variable = getfilestreamargument(oldsavegamefile, 0, "string");
      type = getfilestreamargument(oldsavegamefile, 1, "string");
     if (getglobalvar(variable)){
     variablevaluenewgamei=getglobalvar(variable)+"";
     }else{
     variablevaluenewgamei="empty";
     }
      filestreamappend(newsavegamefile, variable, 0);
      filestreamappend(newsavegamefile, type, 1);     
     
      for (i=1,i<=7,i++){
            variablevalueoldi=getfilestreamargument(oldsavegamefile, i+1, "string");
        
      
            if (i==(gamei)){
            filestreamappend(newsavegamefile, variablevaluenewgamei, 1);   
            }else{
            filestreamappend(newsavegamefile, variablevalueoldi, 1);   
           }
     }
      filestreamnextline(oldsavegamefile);
   }while (variable != "End");   
   filestreamappend(newsavegamefile, "End", 0);
   filestreamappend(newsavegamefile, "int", 1);   
   filestreamappend(newsavegamefile, "1", 1);   
   savefilestream(newsavegamefile, "savegames.txt");
   //free(oldsavegamefile);
   setglobalvar("savegamefile",newsavegamefile);

}

The error was I was trying to append the txt file with int, instead of string.

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