Interview de John Carmack par Beyond3D.com
Nos confrères anglophones Beyond3D ont pu converser avec John Carmack, que ...
Nos confrères anglophones Beyond3D ont pu converser avec John Carmack, que l'on ne présente plus. Dans cette très courte interview assez facile à lire, on y parle de la commande Timedemo et de ses "performances" différentes de celles du jeu réel, du rendering path, etc :
Does that mean you're using different lookups for different materials? What exponent exactly are you trying to approximate?
The specular function in Doom isn't a power function, it is a series of clamped biases and squares that looks something like a power function, which is all that could be done on earlier hardware without fragment programs. Because all the artwork and levels had been done with that particular function, we thought it best to mimic it exactly when we got fragment program capable hardware. If I had known how much longer Doom was going to take to ship from that time, I might have considered differently.
It should be noted that a power function is a strictly empirical approximation of a surface's specular response, so other specular approximations shouldn't be looked at as just approximating a power function. For instance, especially for broad highlights, it is nice to have a finite cutoff angle, rather than the power limit approach.
The lookup table is constant in Doom, so there isn't any real strong argument against replacing it with code. The lookup table was faster than doing the exact sequence of math ops that the table encodes, but I can certainly believe that a single power function is faster than the table lookup.
Accéder à l'interview complète.
Does that mean you're using different lookups for different materials? What exponent exactly are you trying to approximate?
The specular function in Doom isn't a power function, it is a series of clamped biases and squares that looks something like a power function, which is all that could be done on earlier hardware without fragment programs. Because all the artwork and levels had been done with that particular function, we thought it best to mimic it exactly when we got fragment program capable hardware. If I had known how much longer Doom was going to take to ship from that time, I might have considered differently.
It should be noted that a power function is a strictly empirical approximation of a surface's specular response, so other specular approximations shouldn't be looked at as just approximating a power function. For instance, especially for broad highlights, it is nice to have a finite cutoff angle, rather than the power limit approach.
The lookup table is constant in Doom, so there isn't any real strong argument against replacing it with code. The lookup table was faster than doing the exact sequence of math ops that the table encodes, but I can certainly believe that a single power function is faster than the table lookup.
Nil Sanyas
le 10 août 2004 à 14:14
(4 282
lectures)
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