02-23-11 - Some little coder things - Tweakable Vars

So a while ago I did the Casey "tweakable C" thing. The basic idea is that you have some vars in your code, like :

static float s_tweakFactor = 1.5f;

or whatever, and your app is running and you want to tweak that. Rather than write some UI or whatever, you just have your app scan it's own source code and look for "s_tweakFactor =" (or some other trigger string) and reparse the value from there.

So I put this in cblib a few years ago; I use ReadDirChanges to only do the reparse when I see a .c file is changed, and I actually use a C++ constructor to register the tweakable vars at startup, so you have to use something like :

static TWEAK(float,s_tweakFactor,1.5f);

which is a little ugly but safer than the prettier alternatives. (the parser looks for TWEAK to find the vars).

I thought Casey's idea was very cool, but then I proceeded to never actually use it.

Part of the issue is that I already had a text Prefs system which already had auto-reloading from file changes, so any time I wanted to tweak things, I would make a pref file and tweak in there. That has the advantage that it's not baked into the code, eg. I can redistribute the pref with the exe and continue to tweak. In general for game tweaking I think the pref is prefferable.

But I just recently realized there is a neat usage for the tweak vars that I didn't think of. They basically provide a way to set any value in my codebase by name programatically.

So, for example, I can now set tweak vars from command line. You just use something like :

app -ts_tweakFactor=2.f fromfile tofile arg arg

and it lets you do runs of your app and play with any variable that has TWEAK() around it.

The other thing it lets me do is optimize any variable. I can now use the generic Search1d thing I posted earlier and point it anything I have registered for TWEAK and it can search on that variable to maximize some score.