Netvudu Posted December 14, 2011 Share Posted December 14, 2011 (edited) Hi there. I simmed some FLIP stuff around and it looks nice but a bit too fast. Like 30% fast or so. I cached to .bgeo my particles. Although I already suspected some gotcha, I tried retiming with a Timeblend and a Timewarp afterwards, and sure enough something´s wrong. It´s working but there are many frames where I loose a lot of particles. Actually according to Houdini I don´t loose them, but there must be something wrong there because I can see the gaps. As I said, it´s hardly surprising considering its changing topology and I don´t have any substep info. Any ideas before I resim this thing? By the way, is it better to use the scale time parameter at the DOP Network, or to change the fps settings for Houdini? I ask because I seem to recall someone complaining about "Scale Time" changing their sim outcome... Edited December 15, 2011 by Netvudu Quote Link to comment Share on other sites More sharing options...
Sifis Posted December 15, 2011 Share Posted December 15, 2011 Hi there. I simmed some FLIP stuff around and it looks nice but a bit too fast. Like 30% fast or so. I cached to .bgeo my particles. Although I already suspected some gotcha, I tried retiming with a Timeblend and a Timewarp afterwards, and sure enough something´s wrong. It´s working but there are many frames where I loose a lot of particles. Actually according to Houdini I don´t loose them, but there must be something wrong there because I can see the gaps. As I said, it´s hardly surprising considering its changing topology and I don´t have any substep info. Any ideas before I resim this thing? By the way, is it better to use the scale time parameter at the DOP Network, or to change the fps settings for Houdini? I ask because I seem to recall someone complaining about "Scale Time" changing their sim outcome... I 've recently used flip fluids with Timeblend and timewarp and I remember having similar issues. Can you upload your problematic hip to take a look? Quote Link to comment Share on other sites More sharing options...
Ryan Posted December 15, 2011 Share Posted December 15, 2011 (edited) I have done this retiming thing alot before. I actually use a TimeBlend. Then TimeShift and uncheck "Integer Frames". Then I would create a curve in CHOPs or use a keyframe to create a kind of time curve for the "Frame" parameter. I never had much luck with TimeWarp though... I just uploaded an asset on the Houdini Exchange that might help called "Time Driver". Check it out Edited December 15, 2011 by Ryan Quote Link to comment Share on other sites More sharing options...
ryew Posted December 15, 2011 Share Posted December 15, 2011 I just uploaded an asset on the Houdini Exchange that might help called "Time Driver". Check it out Now *that* sounds mighty useful! I will definitely have a look, thanks! Quote Link to comment Share on other sites More sharing options...
Netvudu Posted December 15, 2011 Author Share Posted December 15, 2011 great! that sounds perfect. I will check it tonight. Thanks a lot, Ryan. Quote Link to comment Share on other sites More sharing options...
Netvudu Posted December 15, 2011 Author Share Posted December 15, 2011 I tried the TimeDriver SOP...it´s fantastic!. Thank you for it. I´m interested in the Channel file parameter...did you intend it for CHOP generated files, or for importing something from some other app? Quote Link to comment Share on other sites More sharing options...
Ryan Posted December 16, 2011 Share Posted December 16, 2011 I tried the TimeDriver SOP...it´s fantastic!. Thank you for it. I´m interested in the Channel file parameter...did you intend it for CHOP generated files, or for importing something from some other app? Yea, I was exporting .clip files from another app. But CHOP generated files can work too. I'm glad it helped. Just be aware that it can only handle one Particle System at a time. If you merge two Particle Systems, they will start to jump everywhere. Quote Link to comment Share on other sites More sharing options...
JaydenDP Posted January 13, 2012 Share Posted January 13, 2012 I have done this retiming thing alot before. I actually use a TimeBlend. Then TimeShift and uncheck "Integer Frames". Then I would create a curve in CHOPs or use a keyframe to create a kind of time curve for the "Frame" parameter. I never had much luck with TimeWarp though... I just uploaded an asset on the Houdini Exchange that might help called "Time Driver". Check it out Hi Ryan, this is exactly what I've been looking for, I really want a way to re-time volume fluids without needing all the substep data. I tried using your "time driver" but do you know if there's a way to get this to work properly with my fluid geo sequence? It jitters a lot, here's a quicktime to show what it does at the moment, if I slow the fluid down. Thanks Jay Fluid_RETIME_test.mov Quote Link to comment Share on other sites More sharing options...
JaydenDP Posted January 13, 2012 Share Posted January 13, 2012 Hi Ryan, this is exactly what I've been looking for, I really want a way to re-time volume fluids without needing all the substep data. I tried using your "time driver" but do you know if there's a way to get this to work properly with my fluid geo sequence? It jitters a lot, here's a quicktime to show what it does at the moment, if I slow the fluid down. Thanks Jay Oh sorry, I assumed you meant volume fluids but I guess you were talking about particle fluids. My bad. I really want a ramp-able volume fluid re-timer Cheers Jay Quote Link to comment Share on other sites More sharing options...
Netvudu Posted January 13, 2012 Author Share Posted January 13, 2012 Now, that this is mentioned (yep, it is fo particle fluids), as cool as the Time Driver tool is, I must say I tried it with a FLIP simulation and it didn´t work. At first I thought it did but when I launched a flipbook I got a lot of flickering particles. My initial guess is it´s not actually possible to retime them properly without any substep information. Quote Link to comment Share on other sites More sharing options...
Ryan Posted January 14, 2012 Share Posted January 14, 2012 (edited) I see. @Jayden I never meant for it to work with volumes. I'm actually not very skilled at volumes, they are a whole different beast. @Netvudu I will take another look at the tool. I have used it alot for FLIP fluids, but maybe I should test it with really complex networks. I get flickering usually when some of the ID numbers clash. Like when you have more than one source node or merging multiple particle systems. Edited January 14, 2012 by Ryan Quote Link to comment Share on other sites More sharing options...
Pazuzu Posted January 15, 2012 Share Posted January 15, 2012 HI!!! Look at this example scene, it's part of my research to timewarp fluids (not finish yet!!!) in an efficient way; I choose CHOPs because of the temporal blur feature. it's possible also with timeblent and timeshift nodes but there is no temporal blur. With FLIP you have to not delete any point, dive into the pop solver and disable the kill pop, then in SOPs retime and delete the kill group created in the sim. Cheers. timewarp_fields.rar Quote Link to comment Share on other sites More sharing options...
Ryan Posted January 16, 2012 Share Posted January 16, 2012 @ Pazuzu That's a neat idea. I've never used the VolumeFromAttributeSOP before. The only issue I see is the time it takes to cache the animation data from the points. But other that that, pretty cool. My asset works the same way with using the WarpCHOP, but Im just not generating all those animation curves. Thanks for the idea! Quote Link to comment Share on other sites More sharing options...
ikarus Posted January 16, 2012 Share Posted January 16, 2012 In regards to retiming volume fluids, I think the general idea is to take the density at the integer time step and advect it via the velocity field over the stretched time period, reducing your velocity scale according to the timestep, haven't tried it though. Quote Link to comment Share on other sites More sharing options...
Netvudu Posted January 16, 2012 Author Share Posted January 16, 2012 @Netvudu I will take another look at the tool. I have used it alot for FLIP fluids, but maybe I should test it with really complex networks. I get flickering usually when some of the ID numbers clash. Like when you have more than one source node or merging multiple particle systems. oh!, that might be the reason, because I am merging multiple particle systems indeed...I will try shifting the IDs for one of the sources, and see if it still flickers or not. Thanks for the tip! Quote Link to comment Share on other sites More sharing options...
Pazuzu Posted January 16, 2012 Share Posted January 16, 2012 (edited) In regards to retiming volume fluids, I think the general idea is to take the density at the integer time step and advect it via the velocity field over the stretched time period, reducing your velocity scale according to the timestep, haven't tried it though. I have tested that approach; The main problem relies in that the velocity in those substeps need also the non-divergence projection, if not then when compare the last substep advected with the next integer sim there are so much difference especially on high velocity sims. Edited January 16, 2012 by Pazuzu Quote Link to comment Share on other sites More sharing options...
Ryan Posted January 16, 2012 Share Posted January 16, 2012 oh!, that might be the reason, because I am merging multiple particle systems indeed...I will try shifting the IDs for one of the sources, and see if it still flickers or not. Thanks for the tip! Cool. If you don't want to go through the trouble of trying to shift the IDs, you can try isolating the particle systems one by one. If you middle-mouse click in the node with your particles, you can see the number of 'Particle Systems' there are. Each system is a Primitive. So you can use a DeleteSOP, choose particles as the type and leave isolate one at a time, splitting the tree. Then use the TimeDriver separately and merge them back together. Quote Link to comment Share on other sites More sharing options...
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