Gran Turismo 4 - Over 450 screenshots

[Sprite Machine]

I would believe you.

But I don't. Not today, oh no.

It's TEH TRUTH!!!

What do you think the driver AI is? It's just calculating where your car is and finding paths around it, slowing up, speeding down (erm.. you know) depending on where you are (and lets ignore that GT's AI is rubbish [read: not there] for the time being!).

Now, what is a replay? It's all your controller inputs played back. The AI of the other drivers is just responding to the prerecorded inputs (I've actually seen replays in some games get fecked up and the playback being different what actually happened!! [Driver 2, for example])

So for the replay to work (because it isn't magic, you know, nor is it an MPEG recording or anything!) it has to calculate the lot in realtime, because it's a 'realtime replay' using the engine in realtime. If no AI was calculated in the replay, you'd just have a replay of all the other cars doing nothing!

i uploaded this just for you baby *hug

Awww, thanks.

Looks like a nice in-game shot, eh?

[Sng]

So why does the replay look infinately better than in-game?

Surely when it's replaying something it already knows the paths the AI cars are going so therefore doesn't lose CPU use in working out what they're gonna do?

[squirtle]

So a replay is just a record of your joypad inputs? And all the cars are calculated on the fly to respond to this? Hmmm... I don't buy that in the slightest.

No disprespect, Sprite, but can we have a programmer clear this matter up.

Oh, and Sprite, log on to Xbox Live and accept the friends request I have sent you. It's just sat there at the top of my list taunting me. Please.

[Sng]

Add meee!

(I'm lonely on Live )

[squirtle]

Add meee!

(I'm lonely on Live  )

But we only play FPS on Live with a pad. I didn't think you'd like that.

And aren't you already on my friends list?

[jeff mills gran]

i see that gt4 has the brew making sub-game i've always wanted.

[Sprite Machine]

So why does the replay look infinately better than in-game?

"infinitely"

Because of the camera effects, mainly. The partly zoomed-in/spanning look it has, coupled with the slight 'wobble' of the camera during GT3's replays fooled you into thinking it looked more 'real', because most of that impression of realism in subliminal and far more subtle than you'd think.

Surely when it's replaying something it already knows the paths the AI cars are going so therefore doesn't lose CPU use in working out what they're gonna do?

I don't think it works like that. It would be quite memory intensive to record the actions of not only your own car, but all the others cars as well as a sequence of actions rather than programmed reactions to your own. Certainly games like Driver didn't do that back in the day- it'd be impossible for the PSone's 2Mb of memory; but a different system may be in place for next gen examples such as this and GT3... I just doubt it.

Stop.... confusing... me....!!!

[Sng]

But we only play FPS on Live with a pad. I didn't think you'd like that.

And aren't you already on my friends list?

Hmm, I dunno. I don't think so.

All I know is that I beat everyone from here at any game and I remember they're on my list cos they invite me to voice chat and ask how I'm so good, etc.

[Sprite Machine]

So a replay is just a record of your joypad inputs? And all the cars are calculated on the fly to respond to this? Hmmm... I don't buy that in the slightest.

I can pretty much guarantee that's how it used to be done, as I say, with games like Driver 1 and 2 it almost certainly was!! Plus, it's reeeally easy to do it like that, rather than recording lots of other stuff too, you just 'capture' the player's input!

Oh, and Sprite, log on to Xbox Live and accept the friends request I have sent you. It's just sat there at the top of my list taunting me. Please.

Heh! I've not been on for months!!

I'm sure I added you ages ago though, so erm... yeah!

[Pug Fugly]

So a replay is just a record of your joypad inputs? And all the cars are calculated on the fly to respond to this? Hmmm... I don't buy that in the slightest.

Sounds sensible to me.

Of course, it would only work if there's no random element involved in the opponent's AI. Unless all random actions were based on some kind of seed, or based on the player's input, or the timer or whatever. So even 'random' decisions by the AI are no longer a worry.

And the real benefit is that you only need to record a single joypad action for each 'frame' (or less if you use some basic compression technique).

In fact, when I think of it, it's the easiest way to do it.

What would be the alternative? Plotting the positions of each car for each 'frame', taking into account all the different variables that would need to be recorded, I can see the memory being used up in no time at all. Plus it would involve a lot more effort.

Never really thought about it before, but surely it's the best way, the only way, to do it...?

[robotattack]

"infinitely"

Because of the camera effects, mainly. The partly zoomed-in/spanning look it has, coupled with the slight 'wobble' of the camera during GT3's replays fooled you into thinking it looked more 'real', because most of that impression of realism in subliminal and far more subtle than you'd think.

It's the reflections and lighting too! The reflections are obviously present when you're driving, but you don't see them move across the body of the car when you're driving like you do when you viewing behind the car.

[Boutros]

I'm sure I would enjoy that page, if it was like.... up....

[robotattack]

It is up.

[Sprite Machine]

Some of us can't view it. ISP problems, perhaps? Who you with, Boutros?

[Alex W.]

Replays used to be done with joypad inputs alone, but slight rounding errors and the like could creep in with hilarious effects. I don't know if they just fixed that or something. I can't see them redoing the AI during the replays, though, that'd be silly when they could store off the cars' simulated speed up/slow down instructions instead of the "reasoning" behind it. The files are too large to just be a series of control inputs and the car models/track anyway.

[Venice Cull]

It's the reflections and lighting too! The reflections are obviously present when you're driving, but you don't see them move across the body of the car when you're driving like you do when you viewing behind the car.

It's like PGR2, when you see the replay it looks absolutely amazing - almost real.

I feel sorry for these racing sim developers who create these incredible graphic engines and car details, only for the majority of the game to show the back of the car, the textures flying past unnoticed, and the building details displayed at a skewed angle.

[Sprite Machine]

I can't see them redoing the AI during the replays, though,

Not redo, just let it run its course as normal. It's like, if you drove the same race twice, identically each time, you'd get the same response from the other cars every time.

It's the easiest and most efficient way to do it, and I've rarely seen examples of it going wrong.

that'd be silly when they could store off the cars' simulated speed up/slow down instructions instead of the "reasoning" behind it.

It'd build up an awful lot of data though, wouldn't it? All 6 cars and their entire actions for the whole race? Hmm..

The files are too large to just be a series of control inputs and the car models/track anyway.

The replay files, you mean?

Yeah, never thought of that actually. Maybe they did redesign the way the replays work for GT3. Or perhaps, as is the case with most PS2 saves, the replay is actually tiny and the data and textures for the 3D icon in the menu is using up the rest of the space!

[Kapowza]

*crashes topic*

hopefully the replays will be something that get's fixed for Driver 3, twas annoying in the first game setting up a fantastic chase, only for the replay to show you doing something completly different :/

[Venice Cull]

The replay files, you mean?

Yeah, never thought of that actually. Maybe they did redesign the way the replays work for GT3. Or perhaps, as is the case with most PS2 saves, the replay is actually tiny and the data and textures for the 3D icon in the menu is using up the rest of the space!

I dunno, I mean 'Stop the Express' on the Spectrum would store all the player input in RAM and play the level you've just done back to you.

All that info - in Spectrum RAM. I'm fairly sure they could keep the memory size down in GT - its a three minute stream of numbers isn't it? You could compress that down to a few K couldn't you?

[squirtle]

Not redo, just let it run its course as normal. It's like, if you drove the same race twice, identically each time, you'd get the same response from the other cars every time.

It's the easiest and most efficient way to do it, and I've rarely seen examples of it going wrong.

Not in PGR 2 you don't. I've seen loads of different starts to races with the same cars. I've even not moved from the back and different stuff has happened.

[Sprite Machine]

*crashes topic*

hopefully the replays will be something that get's fixed for Driver 3, twas annoying in the first game setting up a fantastic chase, only for the replay to show you doing something completly different :/

I only noticed that happening when I used cheats. The replay wouldn't show me as 'invincible' even though I was when playing! So I'd end up driving into walls that I never drove into, etc.!

[Sprite Machine]

All that info - in Spectrum RAM. I'm fairly sure they could keep the memory size down in GT - its a three minute stream of numbers isn't it? You could compress that down to a few K couldn't you?

Yeah, I guess so. *shrug*

[Sprite Machine]

Not in PGR 2 you don't. I've seen loads of different starts to races with the same cars. I've even not moved from the back and different stuff has happened.

Hmmm.. the same cars? The same tracks? The same... erm.. whatever else you can change? And different stuff still happens? You mean, the cars that pull away do different things?

*scratches chin*

Meh!

Randomisation, then? I dunno... randomisation scares me. How does one pick a 'random' number anyway?

[Pug Fugly]

Not in PGR 2 you don't. I've seen loads of different starts to races with the same cars. I've even not moved from the back and different stuff has happened.

But a seed generated at the start of the race and used to make the 'random' decisions that the AI makes will account for that. As long as the seed is applied for the replay, it'll work perfectly well.

[squirtle]

Yeah same cars and stuff.

However, it would explain why MSR had no replays because I remember the AI in that being wildly unpredictable. In fact, I would say that the AI in that game is the best example I've seen in a racing game; perhaps Le Mans 24hr being as good as well. But that had full replays...

I have no idea how they do it.

[Venice Cull]

But a seed generated at the start of the race and used to make the 'random' decisions that the AI makes will account for that. As long as the seed is applied for the replay, it'll work perfectly well.

I had this explained to me the other day.

Thing is Squirts, computers are incapable of choosing random numbers, so they do these 'tree' things that spin off all kinds of different numbers. But like Pug said, if the replay uses the same 'seed' number to start with, you'll get exactly the same A.I. outcome.

[squirtle]

I had this explained to me the other day.

Thing is Squirts, computers are incapable of choosing random numbers, so they do these 'tree' things that spin off all kinds of different numbers. But like Pug said, if the replay uses the same 'seed' number to start with, you'll get exactly the same A.I. outcome.

And that's how they do Racing game replays is it? Ok, if such is the case, then how come on the longer replays on the original GT on the PS1 - i'm talking the races which took over an hour to complete - did you only get the first twelve laps replayed (yes I'm that sad that I watched them but at the time I had never seen anything so good so forgive me). Surely if it's just remembering the joypad inputs then it should have been able to show the whole race.

[Juria]

I played the demo of Gran Turismo 4 and it looked the same as Gran Turismo 3, just a couple of the features looked a bit sharper on the car. I hate Gran Turismo 3 because the other cars are so dumb plus they cheat so i'm not interested.. so umm bye... *closes door*

[Pug Fugly]

And that's how they do Racing game replays is it? Ok, if such is the case, then how come on the longer replays on the original GT on the PS1 - i'm talking the races which took over an hour to complete - did you only get the first twelve laps replayed (yes I'm that sad that I watched them but at the time I had never seen anything so good so forgive me). Surely if it's just remembering the joypad inputs then it should have been able to show the whole race.

I guess it depends on how much the game has to remember.

Can't remember if GT made full use of analogue sticks or not, which would impact, but let's just say for the sake of example, you need to store the following information: steering & braking.

If this info could be stored in 1 byte (not sure if it could), and say the game runs at 30FPS. 5 minutes worth of race will need:

5 * 60 * 30 * 1 = 9000 bytes. Which is 9k which doesn't actually seem like that much. Although I'd guess that with GT running on a PS1, spare memory is at a minimum.

Of course, I'm ballpark guestimating all the figures, but I can quite easily see why a stream of joypad instructions would over the course of severl minutes add up to a considerable chunk of RAM (especially on a PS1, which had something like 2 megs was it?).

Of course, I don't know any of this for a fact and could be completely wrong.

[jeff mills gran]

Randomisation, then? I dunno... randomisation scares me. How does one pick a 'random' number anyway?

easy!

just pick a random number >1 and <3