On Sun, 14 Jan 2007 15:52:25 -0800, "James W. Walker" <email@hidden>
wrote:
> On Jan 14, 2007, at 3:14 PM, Daniel Shiffman wrote:
>
>> New to this list. I'm in the process of porting several PC
>> application to Mac (Carbon / C++ / OpenGL). The one last piece I
>> can't seem to solve is how to retrieve the milliseconds() from the
>> system clock. I have an animation that needs to enforce a certain
>> framerate. I'm using usleep() to wait between frames, but I need the
>> milliseconds to determine how long to wait!
>>
>> Any help would be greatly appreciated.
>
> There are a number of functions to get time, such as Microseconds and
> UpTime. I recall an Apple engineer once saying that UpTime was the
> lowest-overhead way to check relative times, but I think that was
> before the Mac went to Intel chips.
Just for the record UpTime (and CFAbsoluteTimeGetCurrent and
mach_absolute_time) is still the lowest-overhead and highest precision clock
on PPC or Intel. (IIRC UpTime & CFAbsoluteTimeGetCurrent both call directly
thru to mach_absolute_time now.)
#import <mach/mach_time.h>
uint64_t t0 = mach_absolute_time();
// do your timed stuff here!
uint64_t t1 = mach_absolute_time();
// compute the delta
uint64_t t = t1 - t0;
// this is the timebase info
mach_timebase_info_data_t info;
mach_timebase_info(&info);
double nano = 1e-9 * ( (double) info.numer) / ((double) info.denom);
// so here's the delta in nanoseconds:
double nanoSeconds = ((double) t) * nano;
// 1000 times that for microSeconds:
double microSeconds = 1000.0f * nanoSeconds;
// 1000 times that for milliSeconds:
double milliSeconds = 1000.0f * microSeconds;
// 1000 times that for seconds:
double seconds = 1000.0f * milliSeconds ;
This in Carbon would be:
AbsoluteTime t0 = UpTime();
// do your timed stuff here!
AbsoluteTime t1 = UpTime();
Nanoseconds nano = AbsoluteDeltaToNanoseconds( t1, t0 );
// if you want that in (floating point) seconds:
double seconds = ((double) nano) * 1e-9;
--
Enjoy,
George Warner,
Schizophrenic Optimization Scientist
Apple Developer Technical Support (DTS)
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