Category: programming

So I released a video yesterday of GSB2 running on multiple monitors, and in that video, a large space battle loads. It takes about 5 seconds. I find those 5 seconds agonizing. I recently spent half a day speeding up the games startup time because launching the game to test 100+ times a day was starting to buy me. Granted, 100×10 seconds is not very long, but I am incredibly impatient. I sometimes launch 2 apps on 2 different monitors and start typing on app 1 whilst windows finishes creating the window for app 2. I often encounter problems where clicking the google homepage and entering a search term means I miss the first few characters as the intel i7 catches up. I’m VERY impatient.

So how did I speed it up? and what tips are there for coding faster loads?

In this case, it was dumbness on my part. Some code that pre-loads ship designs was checking for whether or not lightmaps existed for each ship texture. Some have them, some don’t. It checked by creating the file and loading it in, failing if not found. HAHAHAHA. Very slow, and not needed. Those ships may well not be accessed this game…

So obviously it was tons quicker to not load the file in then, but just to check for the existence of the file on disk (or arguably to do this even later). Cue big speedup. Another speedup was possible because every instance of that item checked for the files existence, so I cached the result in the ship type and only checked for each file once. Much Much Faster.

That’s fine with a game that has few files on disk, but if you need to do this for 2,000 files, it can be real slow just to do those 2,000 file checks. Accessing actual hard drive data as opposed to RAM is painfully slow. With non SSD drives actual physical platters might need to spin. File access is the killer of load times. File access, and decompression.

Ideally you have data on disk that is pretty much in the format it will take in memory, then there is no decompression, just a straight ‘blap’ into RAM. There is a tradeoff here against debuggability, editability and modability. Some games have 2 file formats, a binary version, used when shipped, and a text version that overrides the binary and is only used during development. That can be kinda buggy, and prevents modders accessing the raw assets which might be a bad thing.

Another trick is to use ‘pak’ or resource files. In principle, and often in practice, these are just big zip files. The file access for the entire games resources becomes a single file read, and you effectively load the whole file-access-table for the game in on startup, vastly minimizing file-access slowdowns in cases where there are thousands of tiny files.

In general the golden rule of load times is to only do what you have to. If you can pre-process assets (into binary formats, for example) then do it. If you can defer some actions until that content is really needed, then do it. There is a natural tendency for programmers to have a ‘initapp()’ function and stick everything in there, but you really don’t need to. The player may well not launch the stats screen in this run-through, so don’t load any assets for it, or indeed, any data for it, and don’t waste CPU time initializing systems that might not even be used.

The best advice I could give anyone for speeding up load times would be to just get a profiler. Some are free, most IDEs come with a built-in one (they often suck), and LEARN how to use it. If you never put any time into fixing it, the chances are your load times are laughably inefficient. Most games are.

So here is a thing, you might be interested in if you use STL, if you don’t…well sorry :D

if use use the sort()n function thats built into an STL list, it guarantees to preserve the order of identical objects in the list. if you use the vector version, all bets are off.

Bloody hell.

So if you have a bunch of asteroids with these Z values

5,9,3,0,0,0,-2,-5

And you use a list to sort them, all is good in the world. if you use a vector, those 3 asteroids at 0 are going to Z-fight like crazy things.

the solution?

use stable_sort()

well call me mr-picky but I think I’d be happier if stable_sort() was the default, and we actually renamed sort() to be take_your_chances_and_do_random_crap_sort().

I presume stable_sort is slower… Luckily I’m not sorting asteroids every frame (that would be NUTS), and I only sort things when I have to, so it isn’t mega critical. it led to a bug where the biggest hulk chunks from spaceships did Z-fighting if theyu weighed ewnough to all have a Z-speed of zero, and thus a Z position(relative) of 0, so when other objects spinning away caused a z-sort, their order got scrambled. If you are a non coder and don’t know what Z-fighting is, it’s a flickering effect you get in 3D games where two images seem to be undecided about which one is in front. You often see it on ‘decals’ such as blood splats on the floor or posters on a wall. It’s annoying…

Here is why I reckon that triple-A game runs slow on your PC. The real reason :D

Step 1: Geniuses at Intel / AMD / ARM design an unbelievable;e processor capable of a bazillion operations per second. Efficiency 100%

Step 2: Someone writes a compiler that converts C++ into assembly language / processor specific stuff that makes a lot of assumptions and loses a big chunk of efficiency Efficiency 80%

Step 3: A coder like me waltzes in and writes some code that is as optimized as he can possibly manage, but has deadlines etc and knowledge gaps meaning it’s slightly less efficient than optimal Efficiency 75%

Step 4: He then writes it to run on a single core, because the headache of smoothly spreading tasks over all the cores is unbelievable, plus game code doesn’t multithread easily so… Efficiency 25%

Step 5: Because writing a new engine for each game is un-trendy these days, the coder decides to use an off the shelf engine that makes even more assumptions and compromises… Efficiency 15%

Step 6: Coder #2, not knowing the assumptions Coder #1 made when we wrote those handy functions, calls them every frame instead of once… Efficiency 5%

Step 7: The game gets run on a typical desktop PC, with 30 different apps fighting for CPU and RAM, IM clients, P2P stuff, web browsers, email, all that crapware that shipped with the PC, anti-virus scanners, cool desktop widgets that tell you the weather, music streaming as you play… Final Efficiency 3%.

My numbers are wild guesses, but I reckon there is some truth to it all. For inexperienced coders using off the shelf engines probably boosts efficiency. Maybe some engines under some circumstances on some hardware multithreading is more possible. I can’t help[ fantasizing about a PC that absolutely locked everything down in a big way when you launched a fullscreen game. Turned off everything that could possibly use some CPU or RAM and let the game run like an xbox. Maybe that is what steambox will become?

That’s more likely than many programmers learning how to optimize, that’s for sure :(