This is great! Thanks so much @3dome, I can learn a lot from what you've built here for me. Nice to see how others piece together VEX, always something new to learn!

Very close! Thanks for giving this a go @3dome, it almost works! If I set the num of frames between to 6 and the number of frames turned on to 3, the green dot seems to jump back one spot and then continue forward. I'd also love to implement a frame offset slider into this too if possible. I think some of your code here can help me try to work this out, but if anyone else has any ideas, they'd be greatly appreciated.

I'm trying to make a vex timer that colours a point travelling along a line. I've managed to make a time multiplier control to slow down the speed of the moving colour point, and also a frame offset control to set the start frame for the action to happen. What I'd love to implement is a way to set the amount of time the point is coloured - So if the time multiplier is set very low and the point colour is moving slowly, I'd like to be able to set the amount of frames the coloured point is visible for. As I'm always learning, I'd love if someone could take a look over this VEX and let me know if I've even set this up correctly and I am most open to changes if I have set this up poorly, or it can be shortened in any way. int time = $T*chf("time_mult")*$FPS; int time2 = floor(time - ($RFSTART-1) * chf("time_mult")); int time3 = time2 - chi("frame_offset") * chf("time_mult"); if (time3 != @ptnum){ @Cd = (0,0,0); } else { @Cd = set(1,0,0); } .hip file also attached. VEX_Timer.hiplc

@dleonhardt I didn't quite get the desired result with this method, but I did end up solving the issue by altering some parameters within the Pyro bake Volume SOP itself (it actually gave me a little more control doing it this way too). It turned out to be a bit more simple than I initially thought! I wanted to use the temperature field to control and render the flames, so I used the Bindings tab to re-route the temperature into the Smoke Volume, rather than using the default density attribute. Then I was able to use the Density Scale control to set the desired amount of alpha, and then colour the flames using the Smoke Colour Ramp control. The Density Scale control was super helpful, as it allowed me to dial in the desired amount of alpha on the flames. I did however need to render separate flame and smoke layers this way, but it did solve the issue of having no alpha channel on the fire.

That was it! Thank you so much for this info. Had been banging my head for a few days on this one. Always something new to learn!

Hello! I have a very odd issue with cubic-like blocky patterns appearing in the dense parts of my pyro volume. (This is the indirect emission AOV, as it shows the issue most clearly) Unfortunately I'm unable to post a .hip file due to the project NDA. Some details about my setup: Houdini 19.0.531 - Same issue using both Karma and Karma XPU To get a sense of scale, the explosion takes up about half HD frame size with a voxel size of 0.005 Pretty small voxel size for something of this scale. You can see the bottom half of the explosion seems to hold up to resolution. I'm using the SOP Pyro solver I'm exporting as 16bit float VDB with a resampled velocity volume (although the same issue appears when not resampling and also un-checking 16bit float export). I'm using the Pyro Bake Volume SOP to visualise and apply the Pyro material The only thing that stands out to me as an issue could be the density ranges coming out of the sim are between 0.5 and 1, but the Pyro Bake Volume SOP is pushing this density up to 75 to render. Is this sort of density level something I should try to achieve directly out of the sim, rather than pushing these density levels up post sim? I'm basically using the default render settings, as the issue persists when playing around with various settings. Volume limit is set to 1, as the density of the volume is being lit from an emissive background object (the issue remains when using a normal point light instead).

Thanks for this tip @Atom! Definitely handy for certain situations, although I was hoping to use an animated or moving 3D object in the scene for the matte blocker. I'm not sure this functionality exists.

Is there a way to create a viewport mask object, just for quick flipbooking of objects going behind another object? Say if I had real footage of a tree trunk in my background camera plate - I want to flipbook an object going behind this tree.. Can I use a cylinder in place of the tree trunk and set this object to be invisible in the viewport, but also hide whatever passes behind it? Dare I say it.. Like Maya's `use background` viewport shader.

Yes that's correct. The redshift render has the flame field piped into the density to render, whereas the karma version is only using density for the alpha. That's a good idea - I can try to mimic what I've done in Redshift, although there's so much going on inside the pyro shader, I'm not sure where to start. I would also hope to optimise the number of renders I'll need to output. It would be great to be able to output just the one render, but have the alpha of the flame included the same as it currently displays with density. I do understand that that the normal fire compositing workflow is to simply add the fire on top, although I would prefer to have a less see-though flame, hence why I'm on a mission to create a more solid alpha for the flame.

I've included a quick build of a similar setup, as I'm unable to share the original file due to work reasons. I've built this setup in a couple of different ways to try help explain the issue.. I started out with a redshift fire render, but unfortunately the flame volume does not have an alpha channel (which we need in this particular instance). I can remedy this by simply adding the flame volume to the density field on the redshift volume material, which works without any issues. So far so good, although I need to make use of a deep camera map for volume depth camera blur in post.. So time to make this work in Karma. Karma's alpha channel is not solid in the areas where I have flames - Only where the smoke density is. How can I achieve a more solid alpha channel in place of the flame areas? I have tried deep diving inside the pyro material, but there's so much going on in there, I'm not sure where to start. fire_problem.hiplc

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