In a typical game, there are many things going on at once: multiple enemies moving around and shooting, jumping, etc., music playing, and your actions as well. My question is how does this all take place at once? Are there commands in a language that instruct a program to run two or more portions of code simultaneously? Or do all of these things really happen one at a time, but because processors are so fast we just cant tell?
How do games multitask (or give the illusion of it)?
- Thread starter Special K
- Start date
Some support comes directly from the Operating System -- allows you multiple threads to simulate working in parallel. Rest of it is coded directly in the code (stuff like AI for example).
Actually, they don't do things simultaneously, and you don't even really need threads...
If your videocard would be able to display 1,000,000 fps, you could for example see the one guy moves 1 microsecond before the other guy.
These days, with 1GHz + processor, you can complete 1 simple command in a nanosecond or less, giving you much headroom for 1 microsecond, which you can't even see.
100 fps = 10 ms, which is ages in terms of computer commands...
Most games are designed to react to you, so if you sneak around a corner in Quake 3, and all of a sudden there are 3 enemies there, the program checks: Who can view you, and then for all of the ones who spot you, let the logic decide what to do, and start animating them.
The animation actually takes most of the cycles...
If your videocard would be able to display 1,000,000 fps, you could for example see the one guy moves 1 microsecond before the other guy.
These days, with 1GHz + processor, you can complete 1 simple command in a nanosecond or less, giving you much headroom for 1 microsecond, which you can't even see.
100 fps = 10 ms, which is ages in terms of computer commands...
Most games are designed to react to you, so if you sneak around a corner in Quake 3, and all of a sudden there are 3 enemies there, the program checks: Who can view you, and then for all of the ones who spot you, let the logic decide what to do, and start animating them.
The animation actually takes most of the cycles...
They released the Q2 source? I knew they released Q1 source quite awhile ago. Of course I probably couldn't make much sense of their source code given my limited knowledge but I may give it a look.
Yes you do - otherwise the performance would suffer quite a bit. Threads are critical for Network play for example. Music is also usually run in a separate thread.
I remember that in the days of DOS, programmers used to use the Timer Interrupts to simulate threads
You'll have better luck comprehending Linux source or something
The code's horrible for people unfamiliar with ID's code style.
zephyrprime
Diamond Member
- Feb 18, 2001
- 7,512
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Do games borrow on some of the techniques of operating systems and have thier own "processes" that they manage themselves or do they just keep a list of stuff they have to do and iterate through the list.
Really depends on what kind of services the Operating System provides. For example, if you have multiple threads running, you can change their priority so that they only get a certain % of the CPU. If the game needs even finer control, then yes, the game will simulate taks running like processes. But it is quite time consuming to code, and most programmers will not bother.
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