Thanks everyone for all your answers on this topic. Is seems the consensus
is there no "good" way to do it under windows 9x. The options are JNI,
estimation based on frame rate and possibly JMF library time support.
Thanks again for the input,
Dave Yazel
----- Original Message -----
From: Rob Nugent <[EMAIL PROTECTED]>
To: <[EMAIL PROTECTED]>
Sent: Monday, March 05, 2001 4:35 AM
Subject: Re: [JAVA3D] Java timer, frame/time based calculations
Dave,
I hit exactly this problem also. I ended up writing
a piece of native code to get the time more accurately
which helped a little.
The Windows source code follows, in case it's any use to you.
Rob
NativeClock.java:
package rob.util;
public class NativeClock
{
static
{
System.loadLibrary("NativeClock");
}
public static native double currentTime();
}
NATIVECLOCK.C:
#include "rob_util_NativeClock.h"
#include <windows.h>
JNIEXPORT jdouble JNICALL
Java_rob_util_NativeClock_currentTime(JNIEnv *e, jclass c)
{
jdouble retVal;
LARGE_INTEGER clock_f;
LARGE_INTEGER clock_c;
QueryPerformanceFrequency(&clock_f);
QueryPerformanceCounter(&clock_c);
retVal = (jdouble)clock_c.LowPart;
retVal /= (jdouble)clock_f.LowPart;
return retVal;
}
Rob Nugent
Development Manager
Critical Path Southampton
[EMAIL PROTECTED]
http://www.cp.net
Tel: +44 (0) 1489 585503
Fax: +44 (0) 1489 881363
----- Original Message -----
From: "David" <[EMAIL PROTECTED]>
To: <[EMAIL PROTECTED]>
Sent: Sunday, March 04, 2001 5:25 PM
Subject: [JAVA3D] Java timer, frame/time based calculations
> We do our view changes and animations per frame, using elapsed time to
> calculate rotations in degrees/sec and movements in meters/sec. That way
> our scene stays consistant even if frame rates drop. But I had long felt
> things were not as smooth as they could be and never looked into it until
> now. Turns out that we are getting elapsed time from one frame to another
> of zero very often, causing our scene to be rendered exactly the same as
> several frames in a row, then a draw a new frame then a few copies, etc.
It
> looks like at around 50 fps, I am getting 3 dups for every 1 real frame
> recalc. Course everything still looks right, but I am losing 3 steps of
> smoothness.
>
> For example if I am rotating my view at 90 degrees per second I am doing
> that in N steps, instead of N*4 steps, thus the rotation is not as smooth
as
> it should be.
>
> At 50 fps, I am calculating a frame every 20 ms. I thought the
> System.currentTimeMillis() had a resolution of 5ms, but it looks like I am
> dead wrong. The numbers below look like 60ms, but its probably 50ms. How
> can I get the time to a better resolution?
>
> Dave Yazel
>
>
> In printing out the time stamps I get this:
>
> Frame got elapsed time of zero (last=983725910240, cur=983725910240 [1 min
7
> sec, 55mb]
> Frame got elapsed time of zero (last=983725910290, cur=983725910290 [1 min
7
> sec, 55mb]
> Frame got elapsed time of zero (last=983725910290, cur=983725910290 [1 min
7
> sec, 55mb]
> Frame got elapsed time of zero (last=983725910350, cur=983725910350 [1 min
7
> sec, 55mb]
> Frame got elapsed time of zero (last=983725910350, cur=983725910350 [1 min
7
> sec, 55mb]
> Frame got elapsed time of zero (last=983725910350, cur=983725910350 [1 min
7
> sec, 55mb]
> Frame got elapsed time of zero (last=983725910400, cur=983725910400 [1 min
7
> sec, 55mb]
> Frame got elapsed time of zero (last=983725910400, cur=983725910400 [1 min
7
> sec, 55mb]
> Frame got elapsed time of zero (last=983725910400, cur=983725910400 [1 min
7
> sec, 55mb]
> Frame got elapsed time of zero (last=983725910400, cur=983725910400 [1 min
7
> sec, 55mb]
> Frame got elapsed time of zero (last=983725910460, cur=983725910460 [1 min
7
> sec, 55mb]
> Frame got elapsed time of zero (last=983725910460, cur=983725910460 [1 min
7
> sec, 55mb]
> Frame got elapsed time of zero (last=983725910460, cur=983725910460 [1 min
7
> sec, 55mb]
> Frame got elapsed time of zero (last=983725910510, cur=983725910510 [1 min
7
> sec, 55mb]
> Frame got elapsed time of zero (last=983725910510, cur=983725910510 [1 min
7
> sec, 55mb]
>
>
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