Retiming Realflow Sim

Deprecated Krakatoa 1.5 Beta Discussion
1

Hi there,

when retiming a realflow sim it seems that the velocities are interpreted weirdly (or velocities are inverted).

If i animate the graph in the prt loader non linear then it seems that from Sim-Frame to Sim-Frame the
animation runs backwards and then jumps to the next frame.

In the last project i ran into this i did a quick script controller to round to the next integer, but that’s just
a very ugly hack. Anyone encountered that already ? Or is it just me ?

Regards,
Thorsten

2

When going sub-frame by using the PRTLoader’s Graph option, are the subframes interpolated by the velocities of the previous and the next frames ? If so is there
a way to invert velocities before retiming ?

Regards,
Thorsten

3

I just tried negating the velocities via KCM, exporting as .prt and loading back in…same thing happens. Is there subframe states saved ??

Regards,
Thorsten

4

Can you send us an example to play with?
Sounds like a bug, but I have never worked with Realflow myself for obvious reasons so I have never seen that happen.
The sub-frames are indeed interpolated based on the positions and velocities of the closest frame and there might be something wrong in the way we read the BIN data or something else…

5

Sure thing. Sending the example i am working on wouldnt be practical due to cache size. But i’ll prepare a small example that behaves like described above.

Thanks in advance!

Thorsten

6

Here’s a quick example. The realflow scene is simply a circle emitter and a gravity.
Then i loaded the .bin in a prt loader. switched to graph mode and animated from frame 50-100 across the default time-range of 0-100.
It shows clearly that during subframe interpolation the interpolation is reversed.

Kind regards,
Thorsten
realflow_prt.zip (1.25 MB)

7

Looks like RealFlow stores velocities in units per second, while Krakatoa does it per frame.
You can add a KCM, divide the Velocity by the FPS used in RealFlow and resave as PRTs.
Then the retiming will work as expected.
Notice that the velocity display of the BIN shows lines that are too long. PRT Loader is supposed to show a line from the position of the particle to the position it will be at on the next frame, but it draws them about 30 (24?) times longer…
We will look at this internally, but you can work around with a KCM for now.

8

Thanks a whole lot Bobo…that’s gonna save me from a lot of linear retiming in Realflow and retiming with rounding :smiley:

Regards,
Thorsten

9

I was wrong, PRTs are Units/Second, we just display the velocities correctly per frame.

We found out via the RF FAQ that there is something called Global Scale in RF.
realflow.com/faqrf/faq.php?category=8

So the big question is, what is your scale in RealFlow?
Krakatoa assumes the scale to be 1.0, but it looks like your velocities are around 10 times larger than they should be, so we guessed you were using a different scale. (NextLimit suggests a factor of 0.01 for Max work).

Can you send us a screenshot of your File>Preferences page in Realflow?

10

Darcy figured out that you have been using FPS of 250 in your simulation - is that right?
Max goes only up to 240, when you change Max FPS to 240 you get a relatively nice retiming.

So you could divide the Velocities in a KCM by (RealFlowFPS/MaxFPS) and resave.
Then load the resulting PRT files and they should retime correctly.

Unless we are missing something.
So it is not a Krakatoa bug but an FPS mismatch. You cannot expect to use different settings in the two applications and still have correct behavior.

Cheers,
Bobo

11

Uff. Well…to be honest…i didnt know max tops out at 240 fps…and in addition i didnt expect it to make any difference, as
it just saves out a bin per frame…taking into the equation that veocities are measured per frame that does make sense to some
extend…

Thanks a lot for investigating that much…it’s kind of a bitch (realflow that is)…and now it’s max sigh

I cant really tell how pissed off i am off nextlimit regarding realflow’s pricetag. The max exporter doesnt work. It crashes without warning
for far particles. It cant go past 4GB even with the 64bits bui.d and in general is a PITA.

And i couldnt really lower the fps as realflow is bitchy about pretty much every single parameter it’s got…scaling and fps beeing pretty
much the worst…i’ve been asking for flood without reply…so go go go… you got an immediate client raising his arms in agony :stuck_out_tongue:

Thanks a lot again and i’ll take a deep look tomorrow…

oh…and greetings from Lele btw…his flight got canceled but he got back this evenig :slight_smile:

Regards,
Thorsten