Game Design, Programming and running a one-man games business…

Category: democracy 4

Pak files

I just added pak file support to Democracy 4. Its something I already had coded for an earlier game, but I had to do a bit of fussing to get it to work properly with democracy 4.

Pak files are basically big phat files that contain other files inside them. If you are a new developer, you probably have no idea they exist, because you probably use unity and AFAIK they handle it for you. Pak files are pretty old school, as I recall Doom and Quake used them (maybe called wad files), anyway the principle is pretty simple:

A pak file contains two sections, an index that tells you where all the other files are inside the main section, and a big phat list of data that is the contents of those files. All of this gets stuck in a single flat blob of binary data. A class exists that lets you grab the memory address of the file you want if you pass in the name of the file, so hopefully to anybody who didnt write the pak file code, using it is easy. You can read the contents of a file just like its on disk, except you have to use functions that read from memory, not ones that explicitly read disk files.

In my case, that meant stepping into the engine code, and the opengl stuff that reads in graphics files (we are only using a pak right now for dds and pngs), and just changing the contents of one function. Instead of using this code to load the data ready for creating a dds:

fread(filedata, filesize, 1, fp);

I now use this

memcpy(filedata, GetPakFiles()->GetData(pentry->StartOffset), filesize);

Big deal :D. Similar changes happen for pngs. To keep things super-simple, the old code for loading a file will run if the pak file reports it cant find that file, so you can stick a ‘loose’ png or dds file into the bitmaps folder structure and it will still get found, and the rest of the code doesnt even know the difference, which is perfect for mod support.

Most of the hassle in getting this to work was just writing some code to enumerate (that means list really…) the contents of a folder from within the pak file. I had to support this for stuff like minister profile pics, because the code previously would ask ‘what files are in this folder, I need to know so I can select a random one’, and now that code gets handled by the index at the start of the pak file instead.

So why bother with this?

Basically speed. Do you know wwhat the read speed of your hard drive is? Checking a random new one on amazon.com shows 6Gb/s. I assume thats bits not bytes, so thats 750MB per second. My hard drive is a little bit older, so lets say 500MB/second. I’ll just copy a big chunk of the source and obj files from D3 to another disk, brb…

Ok…copy speed is between a low of 1MB/second up to 100 MB/second. Wow. Thats so much slower. Why?

A HUGE amount of bullshit happens on a PC when you access files. To simplify it, it goes something like this: *deep breath* You ask to read in a file. The OS then looks up the file table to check that file exists. it then asks the security system if the current user has permission to access that file. When it gets a yes, it then opens that file, and sets attrributes so other processes will know that file is in use. The antivirus software then kicks in, and hooks into the file read so that it can check to see if that file is excluded from scans or not, and gets ready to analyze its contents. The O/S then has to use the file-table to work out where all the various scattered chunks of that file are, and start reading in each block. This means talking to the driver, and ultimately to the hardware, which may also have to check its cache to see what blocks have been cached and whether or not it has to start the glacial process of spinning an old physical drive or not (faster with SSDs obviously).

THEN! when the file read is complete, we can close that file again, notify the system that its not in use by our process any more. We can then start the process of opening the next file in our list..

You do that bullshit for EVERY DARNED FILE. But the good news is… if you have a big phat pak file…you do it once. Just once. The rest is free.

So Democracy 4 goes the extra mile, because our pak file is small (only a few hundred MB). We dont just open the file on startup, we stream all 200MB into RAM. That should take way under a second. We then have the entire file system of dds and png files in memory already, and able to be loaded almost-instantly into our engine. (RAM->VRAM is mega fast)

99% of players will not notice the speed difference. But if you have especially shit anti-virus running on a laptop, in low-battery mode, with an extremely fragmented hard drive, running democracy 4 on a train, you will be glad I bothered. Its really easy to code. My PakFile code has 263 lines in it. Many of them are whitespace or comments.

Democracy 4: The fixed income rewrite

About a week ago I had this mad idea that it would be cool to plot every single Democracy 4 voter’s wealth on a graph, so that you could see where they were clustering in a nice easy-to-understand way. Within an hour it worked, within a day, a new rewritten version that looked much nicer with blue dots on it was done, and I was tweeting, and people were saying ‘yay’, and then everything went fucking mad.

By hovering the mouse over one of those blue dots, you could see a breakdown of how that persons income was affected by every government policy or situation, indirectly, through their membership of voter groups. This data already existed in Democracy 3, it was easy, it was just GUI code, and done really quick… and that showed me what an absolute mess the simulation was…

Democracy 1,2,3 and 4 are all coded as a homebrew neural network. Every neuron has a value either capped from 0->1 or -1->+1. Everything in the game is a neuron, a voter, a voter group, a policy, a minister, an event…everything. Voters also have an ‘income’ neuron which tracks how much money those voters have. So…in supersimplistic terms if you want to know why Bobs income is 0.78, you look at the 21 weighted inputs from all the voter group income neurons, and you see all the +0.2, -0.1,+0.32 etc, that adds up to 0.78. If you want to go one stage further up the hierarchy you can track the origins of those effects to policies etc.

Thats worked for 3 games perfectly. But its a crap system.

The trouble is, peoples incomes are on a 0->1 scale. And all effects are percentages. So for example if free bus passess give retired people a 0.05 income boost, that increases the income of all retired people by 5%. Fine?

NO

Because working class ex-street sweeper mavis just got a bus pass worth $500, but retired hedge fund manager Boris just got a buss pass worth $15,000. WTF? why does democracy hate poor people? The problem is that we have only ever been able to use effects to apply percentages to incomes. That means EVERY benefit, or tax, or effect is proprotional to your income. That means lambourghini drivers pay more in car tax than skoda owners (maybe intentional), but means the state pension depends on how wealthy you already are.

Its fixed. it was hard.

Basically I have had to code an entirely new shadow system of fixed-income neurons that can cope with values beyond 1, and then (this is the hard bit) written code that stitches it all back together internally so that we can still use the same mechansims to move people between middle-income and poor etc, and still display everything in the UI as though nothing has changed.

This was hellish, because it also means restitching together lists of totally different UI items on the fly with different calculation methods to come up with a result that looks the same as it used to. Its taken a week of fixing edge cases, checking, altering UI, and writing lots and lots and lots of code which mostly will go underappreciated :D.

But thankfully it now works, and it means we can have effects in the game which are +10% income of retired people, and also effects that are +$10,000 income of retired people, as the designer or modder sees fit. This means helicopter money can actually be fixed for everyone, free school meals no longer serve foie gras to rich students, and so-on.

You wont notice it immediately but its a massive improvement in the underlying simulation code in the game. It stressed me and tired me out so much to do it that im forcing myself not to code today so I can recover.