I need a high precision timer (cocoa)

[rasteblaster]

I'm new to MacOSX programming.

I need to get a high precision clock to use with my game engine.

Something that gives me the time in milliseconds.

Any help would be greatly appreciated,
chris

[OneSadCookie]

+[NSDate timeIntervalSinceReferenceDate]

Returns a double, 1.0 == 1 second, accurate to well below milliseconds.

[imported_kelvin]

NSDate *reftime = [NSDate date];
double howmanysecondselapsed = [[NSDate date] timeIntervalSinceDate:reftime];
slightly easier to manage.

[belthaczar]

NSDate *reftime = [NSDate date];
double howmanysecondselapsed = [[NSDate date] timeIntervalSinceDate:reftime];


Umm, wow, that looks incredibly easy compared to what I had been using:


UnsignedWide currTime = {0, 0};
Microseconds(&currTime);
double time = UnsignedWideToUInt64(currTime) / 1000000.0;


I don't suppose anyone knows why I would have used such an ugly piece of code when there was a nice solution in Cocoa?

--phillip

[imported_kelvin]

90% of learning Cocoa is figuring out what classes do what. I find most common things are not obvious until you've done them once or twice.

[rasteblaster]

Thanks to everybody for the quick replies!

[arekkusu]

Milliseconds are not really high precision. At 60fps you have a 16 ms window, a 1 ms error is enough to make your fps counter wrong.

gettimeofday() will give you time in microseconds.
UpTime() will give you time in nanoseconds (obviously not at 1 ns precision...)

[ThemsAllTook]

Unless I'm greatly mistaken, UpTime() gives you microseconds, not nanoseconds...

Alex Diener

[imported_kelvin]

NSTimeInterval = double = 8bytes = 64bits

From the documentation, The NSTimeInterval type makes possible a wide and fine-grained range of date and time values, giving accuracy within milliseconds for dates 10,000 years apart

10k years = ~315360000000 seconds.
divide by 64bits = 0.000 000 01709 seconds

sub-microsecond accuracy, probably even after you account for the floating point bits.

I'd say NSDate is plenty accurate for any needs.

[OneSadCookie]

sub-microsecond precision, not accuracy :)

A double only has 53 significant bits.

[arekkusu]

UpTime() returns the value right from the PPC tb register, which you then convert into nanoseconds. I'm pretty sure [NSDate timeIntervalSinceReferenceDate] is doing exactly the same thing but converting to floating point seconds. No problem there, I'm just responding to the initial question with the observation that measuring in milliseconds (i.e. glutGet(GLUT_ELAPSED_TIME)) isn't good enough.

[imported_kelvin]

ok with 52 significant bits (http://www.freesoft.org/CIE/RFC/1832/10.htm)... that gives... 0.000 070 seconds precision. Still fine for most uses.

500fps only needs 0.002 seconds.

[arekkusu]

Getting off topic now but what if you want to do more than post a fps number? Say, measure how much each bit of your rendering is taking per frame? :) I.e. how much time building objects, rendering audio, submitting vertices, etc. There's a definite need for sub-millisecond precision. Look at MAME's profiling.