[SDL] writting a doom-like game
prefect_ at gmx.net
Sat Jan 8 08:53:58 PST 2005
On Tuesday 04 January 2005 16:22, Bob Pendleton wrote:
> There are a lot of things that were done in DOOM that are not worth
> doing now. For example, DOOM used fixed point arithmetic, but modern
> processors (486DX and above) do floating point math very well, so there
> is no need to deal with fixed point arithmetic.
There are still some niches where fixed point is valuable. Whenever you need
to store some vector that is supposed to have equally distributed precision
across its entire range, and you're not doing seriously heavy math with
this vector, you might want to consider fixed point.
In one 3D environment, I was reaching the range limits of the 32 bit float.
Well, not exactly the range limit, but once you're too far from 0 (i.e. the
world origin), the precision got so bad that round-off errors in simulation
were unacceptable. There were two choices: Use double, which takes twice
the memory, or store the actual coordinates as 32 bit fixed point. I chose
the latter, and it works perfectly fine. Note that I still use float during
the actual simulation, but that works out fine because during the
simulation, only small (difference) vectors will be used.
To give a more well-known real-life example, Half-Life sends player
coordinates as fixed point across the network. This is obviously done in
order to save space while guarantueeing that the precision at which player
coordinates are transferred is everywhere the same.
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