I am quite sure that the physics engine is not modified while using AR MAX. I believe it's simply changing the data that the engine interprets.
It 'could' represent car data, but as I said before, the physics for a car are non-linear. Putting this into example will probably make things clearer...
The 1886 cars have 1BHP and go around 10mph. The various Le Mans cars in GT4 have around 1100BHP, and go about 350mph when tuned right. The current world land speed record holding car Thrust SSC has 110000BHP, and is capable of 850mph. At the same time though, the Le Mans cars will accelerate to 100mph much faster than Thrust SSC does (because jet powered cars have a spool up time and a large inertia due to thier weight).
If we plot these on a graph, we see that there is no simple formulae that matches all the data, because things like aerodynamics and suspension and the weight of the car all play a part. We cannot simply multiply the horsepower by a factor of 8 and hope to achieve 8x acceleration, because the other factors will then come into play differently. Because of this, its very difficult to achieve exactly 8x acceleration at the cars data level, and certainly not possible to make a simple generic cheat that would work for all cars.
On the other hand, by changing a constant in the underlying formula by a factor of 8 (that is, multiply or divide by 8), then we can achieve this much more easily. This is because we dont need to know anything about how the game interprets/applies car data at this level, we simply just scale the output to achieve our result. Almost all physics engines contain some constant scaling values already, so targetting and modifying these is the easiest way to achieve our result.
Although that modification may be trivial (and possibly achievable by changing the car data instead, albeit with difficulty), in my opinion it is still a change to the underlying game engine.
Can somebody please explain to this
person how replays are saved... Somebody who actually knows what they're talking about (possibly MasterStorm) would be preferable?!
In regards to the saving of replays, rather than storing a series of images and sounds, Gran Turismo instead saves a timeline of button presses. When the replay is played back, it simply reads back these button presses and applies those to the car, rather than reading from the game pad.
This is like how a music box works, where pins along a sheet of paper cause notes to be played. The paper does not store any actual sound, only the pins which tell the music box what to do.
Because we only have the keypresses to go by, and not a series of images, then if the replay was recorded with cheats present (for example the 8x acceleration), then these must also be active when the replay is played back, otherwise the button presses in the original run and the replay will be interpretted differently, and will not look the same.
This would be like putting our sheet of music into a different music box, where it might play out of tune or maybe play faster/slower.
Because whe need to have all these cheats present, and because some of them require precise timing of application (the mega turbo cheat I think was mentioned), it makes it very difficult record the replay, because replicating the run is very difficult (due to the timing). It's not impossible, but I can imagine it would take a lot of time, which when your trying to record as well can be frustrating.
Another example, as opposed to the music box would be the MIDI file format, where only the notes and an instrument ID are stored, rather than any actual sound. The notes are reconstructed back into audio during playback, much in the same way GT replays are reconstructed from the keypresses. Like the GT replay files, this is the reason why MIDI files are so small.
Btw, the only sensible reply i have recieved in this whole thread is from MasterStorm, he brings something of knowledge to all of this silly little drama, so before you all make up your own ideas about how a physics engine works, consult him.
Thankyou.
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