Hi thanks so much @Benyee for outputting this file again. I can understand the workings behind this now thank you - So it's all about matching the original vel from the fire sim to create the particle trail which in turn passes the masking attribute over to the flame mask. It's quite the workaround, but looks like it's doing what I'm after. Again thank you for this, it'll help me out a lot!

@ryew this is the process I'd expect to work, I'm just not sure how I'd go about creating those attributes. Thanks @Benyee thanks for going to the trouble of building an example scene, although I'm afraid it seems corrupt when I open. A few of the nodes have been replaced my merge SOPs, which I think can happen if the file is corrupt - Or possibly the file was created in a newer version of Houdini than what I'm running here (19.0.383) due to needing the Redshift plugin.

Title is a bit misleading.. I realise Pyro volume simulations don't really have a birth and death point, but what I'm hoping to achieve is to be able to colour or alter the transparency of my fire closer to the base or emission point of the fire. Currently my fire is looking really nice, apart from the base of the fire where it first emits from. I'd like to make this area more transparent. I'm using the Redshift volume shader, but unfortunately cannot post a .hip file due to work non disclosure stuff. I can create a simplified version of the scene if need be.

Thank you so much @madebygeoff! This function is going to come in very handy for me. Taking notes now! The world of quaternions is slowly becoming easier to understand.

Hello! I'm copying a bunch of flat pentagon shapes to points. All of the copies are facing the correct direction except one: I first set a perpendicular N direction on the points to copy to, which helps the pentagons get copied almost in the right direction. Do I first need to aim the orient direction of the points toward a specific direction? I have included a hip file with something I think might work, but I'm just not sure how to turn two vectors into an orient. Any help is greatly appreciated! orient_toward_specific_point.hiplc

Beautiful! This is exactly the sort of control I was after, thank you @Ziyad! Thanks for your input too @PixelNinja, although this method does not keep the point active for just one frame at a time.

Hello Houdini vex wizards! I'm having a lot of difficulty trying to come up with a solution for this one myself. As the title mentions, I'd like a single point to be created for just one frame and then disappear again - I would also like this to happen at random time intervals as the frame number increases. For example the point will flash on for 1 frame, then maybe nothing for 10 frames, or nothing for 2 frames, then another point flash and so on. I'm not very good with time related things in vex, but would love to learn more about random time stuff if anyone has any ideas?

Both of these are yielding good results. I initially thought an if statement wouldn't quite do it for the sim, but it seems to be going in the direction I'm after. Thank you!

Hello! Does anyone have any experience with making use of Houdini's whitewater volume gradient to help add reflections to the whitewater volume? Is it possible to make use of this volume gradient in Redshift? The RS volume material doesn't have many controls, but I thought I might be able to make use of the emission channel in place of bright white reflections maybe. Any ideas would be greatly appreciated.

The following expression on a popwind dop node will make the faster moving particles have more amplitude according to the noise settings: amp = length(v@v); But how can I go about making only the slower moving particles be more affected by the pop noise? Instead of just using a general if statement to say if particle speed is less than a certain amount, then have noise applied.. I'd rather the amplification of noise be more apparent as the particle speed gets lower. Thinking back on this, maybe it does not make sense at all.. If a slow moving particle is then pushed around faster by the noise, is it then considered as moving too fast and therefore the noise should not be applied? Have I thought up an impossible noise equation here?

I ended up solving the issue by first using the Orient Along Curve SOP (which is an amazingly handy SOP that can do so much more than just this!) to first build the orient attributes, before the hair curve goes into the Vellum network, then point deforming the low res hair curve back onto the high res one.

Thanks @ryew Apologies I did not mention I had tried this method already. While working on the first level of hairs (I'm building a dynamic tree), each new level becomes less and less stable with this method unfortunately. I think it is ok that the input curve comes in without the orient attribute, as it will always come out of the Vellum solver with one. I tried many different ways again after posting this with no luck unfortunately - Another option I can try is sticking with just the high res input curve and cranking up the constraint iterations and substeps until the hair curve is rigid enough to be as solid as a tree trunk. The only problem here is the sim time. Things start to get unmanageable when just a single curve needs to be 25+ substeps with over a thousand constraint iterations! If anyone has any methods for keeping Vellum hair rigid I'd love to hear

I have a single Vellum hair with many points. To help make the sim faster and also keep its rigidity, I've first resampled the hair before going into the solver. Everything works well here, the hair is bouncing and coming to a halt exactly how I'd like it. Next I'm using the Guide Deform SOP to transfer that Vellum dynamic movement back onto the higher res original curve. This is where my problem starts. The point orientation has now lost its data. Is there any way to point deform one object to another and keep the point orientations correct? I'll attach a simplified .hip showing the issue with both the correct and incorrect point orientations. Any help is greatly appreciated! Orientation_Problem.hiplc

Thanks Alvaro! So strange.. this simple .hip setup is a smaller version of my main scene and I had already tried setting those two functions without any luck! I have tried again today and what do you know, it's working finally. I think the problem could have been a mixture of higher viscosity and not enough slip source scaling on my main scene. Anyhow, working now and I have this example file to reference for next time. Thanks for your help!

I have a very simple setup which is trying to utilise a custom flip fluids slip field. Just a simple sphere emitting fluid which hits a collision surface. I have set up a slip field on just one half of the collision object, but I can not for the life of me see any slip difference between each half. I have checked the old H16 flip fluids masterclass video which talks about the implementation of the custom slip field, but didn't state how to create that field. What have I done wrong? Here you can see the slip field on one side of the collision object. .hip file attached Slip_Field_Problem.hipnc