4 ms·

My experience is that double precision is very common on demanding game areas, notably physics. I recall older versions of the ODE physics engine recommending a

by tgb 10y ago

My experience is that double precision is very common on demanding game areas, notably physics. I recall older versions of the ODE physics engine recommending and defaulting to double precision and lots of newbies on the forums being surprised there wasn't much performance difference. That was all some time ago.

yoklov 10y ago
My experience is that it's extremely uncommon, including on physics systems. While I no longer work in games, I did for several years, I probably can count the times that I used double precision on one hand (if you exclude the JavaScript work that plagued the end of my game development career). The reason for this is simple -- it's twice as slow. The vector width is half the size, and so you can do half as many operations at a time.
- tgb 10y ago
  My experience is just as an amateur, so it's only worth so much. I'm pretty sure though that the difference was much less than a factor of two.
  - loup-vaillant 10y ago
    Probably because double precision floats are just as fast as single precisions if you don't vectorise. I bet you didn't. This would also explain for instance why many programming languages drop single precision floats altogether: they don't plan to vectorize in the first place.
    - tgb 10y ago
      Yeah, it looks like ODE doesn't use SIMD or anything, and hence performs poorly compared to more modern engines: http://blog.wolfire.com/2010/03/Comparing-ODE-and-Bullet http://blog.wolfire.com/2010/03/Comparing-ODE-and-Bullet
zubat 10y ago
A pretty solid rule of thumb is that 32 bits has enough precision for rendering, physics needs doubles if it's going to use a lot of iterations. Simplified models like Super Mario jumps or the tractor beam in "Thrust" (single rigid joint) can get away with 16-bit fixed point precision. OTOH rendering of geometry only needs about as much precision as the display offers, which often means 8 bits on older hardware.

by tgb 10y ago

yoklov 10y ago

My experience is that it's extremely uncommon, including on physics systems. While I no longer work in games, I did for several years, I probably can count the times that I used double precision on one hand (if you exclude the JavaScript work that plagued the end of my game development career). The reason for this is simple -- it's twice as slow. The vector width is half the size, and so you can do half as many operations at a time.

tgb 10y ago
My experience is just as an amateur, so it's only worth so much. I'm pretty sure though that the difference was much less than a factor of two.
- loup-vaillant 10y ago
  Probably because double precision floats are just as fast as single precisions if you don't vectorise. I bet you didn't. This would also explain for instance why many programming languages drop single precision floats altogether: they don't plan to vectorize in the first place.
  - tgb 10y ago
    Yeah, it looks like ODE doesn't use SIMD or anything, and hence performs poorly compared to more modern engines: http://blog.wolfire.com/2010/03/Comparing-ODE-and-Bullet http://blog.wolfire.com/2010/03/Comparing-ODE-and-Bullet

zubat 10y ago

A pretty solid rule of thumb is that 32 bits has enough precision for rendering, physics needs doubles if it's going to use a lot of iterations. Simplified models like Super Mario jumps or the tractor beam in "Thrust" (single rigid joint) can get away with 16-bit fixed point precision. OTOH rendering of geometry only needs about as much precision as the display offers, which often means 8 bits on older hardware.