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Everything posted by Fireandsmoke

  1. Apply detail to smoke using Volume Procedural

    Thanks. Yes can see a difference in the viewport but have you tried rendering it? I just get black from the second version (which was also happening when I tried to build the vop according to your picture) An issue seems to be that the "density" inside the cvexvop is not referencing the density of my preexisting volume. Because even the following in the cvexvop will render black.
  2. Apply detail to smoke using Volume Procedural

    Thanks Noobini. I can see your theory here but it doesnt seem to be working for my set up. Would you mind sharing your .hip? Thanks
  3. Compensate for slowing FPS/Timescale

    I've been playing for days and days trying to slow smoke sims for some nice particle advections. They need to be very slow, so the process I've been trying to use is either reducing the timescale, or cranking up the FPS of my timeline. At these slow speeds, it is not practical to find the "look" of my sim, I need to look dev at 25fps, and then slow that version down. But by then slowing down the sim via timescale or FPS, only rarely do I get a result I want. Is there settings with the solver or DOPnet that I need to be adjusting to compensate for the slower speed? Most of the time, a beautifully turbulent and dynamic sim at 25fps often just turns into a hopeless blob at 200+fps or 0.1 timescale. Would love some input on this.. (PS. Im still on 16.5 for now, so the retime node is not an option). Thanks
  4. Houdini 18 Wishlist

    More VR tools, particularly a HMD preview mode, if not from the viewport, then from a flipbook (which would require a top/bottom latlong veiwport display from the spherical camera), or even the render window as a last resort. This would make Houdini infinitely more usable for VR.
  5. Compensate for slowing FPS/Timescale

    For my own understanding, I'd really like to know why changing the timescale parameter changes the look of the sim so much? I thought its function was to scale the time base of everything inside the solver, so why does it then cause such huge change - a basic smoke sim at timescale 0.1, 1 and 5 are all going to look completely different... which makes it kind of useless.
  6. Smoothing volumes

    Thanks for that. Sounds like from some other sources that RS does not have a similar feature. However I need to stick with RS for fast render times. So is brute force voxels the only way for me achieve a dense looking volume with no visible voxels? Are there any tricks or tips you can suggest for keeping my voxel count high and volume smooth, without crushing my pc? Thanks
  7. Smoothing volumes

    Hi, I'm fairly new to volumes so please bare with me.. I'm enjoying creating some cool effects with Houdini volumes and Redshift by simply assigning a Redshift volume material and cranking up both the Scatter and Absorption coefficients of the density to get some cool sci-fi-ey gaseous effects where the volume has an appearance of being quite thick bodied yet translucent. The problem is that dialling up the density like this in the material means the voxels become very defined. So I'm wondering if I'm going about this the wrong way? Or is there a way to smooth my volume out? Im aiming for a 4K output for a big screen so it will need to be very smooth. Ive tried cranking the voxel count to 600 (Max Axis), as you can see below still quite visible. Also tried a Volume blur (and converting to VDB and using VDB Smooth), which helps a bit, but it loses the overall effect and still leaves a moire-ish pattern from the voxels. Thanks for any suggestions
  8. I've got a simple particle setup, a large number of particles being advected by a smoke sim and then cached out to a bgeo. Then loading that into a File sop and using a delete SOP with a Delete by Range (29 of 30) to dramatically thin it out for some close ups. This process has been working well for me across a variety of different particle setups, but for some reason on this shot, my particles hit a certain frame and go bonkers. There is nothing wrong with the actual sim, so I can only put it down to being something to do with the delete SOP. https://giphy.com/gifs/X9jk5OOy7tvaHYtUwR Any ideas what this might be causing this? And any way to fix it without changing my existing geo, as I had already rendered hundreds of frames before I noticed this problem and would love to not have to redo the earlier frames, if possible. Thanks for any advice
  9. Compensate for slowing FPS/Timescale

    Thanks Atom, this looks good. Have you used this setup before? Ive tried copying this retime setup into my own pyro sim but its not working as in the original .hip, just plays back both at the same speed. EDIT: Just noticed that this actually involves the installation of a custom asset library.. then it will work..
  10. Retime sim

    I've seen a few responses to this question, but still am having no luck, wondering if someone can hold my hand and give me some specific instructions. I simply want to retime a VDB of smoke to make it slower, interpolating between frames. I've got a VDB which I've cached out and loaded back in via File SOP. Now I've added a Time Blend, and then a Time Shift. In the TimeShift I've changed the Frame expression to $F*0.5 and unchecked Integers. I'm still not seeing any interpolation between frames. What settings do I need in my TimeBlend for this to work? Thanks a lot
  11. Make smoke follow a curve

    Many thanks for the link, good find!
  12. Make smoke follow a curve

    I'm trying to make billowing smoke follow a spiraling curve, kind of as if a tornado did a corkscrew. I know with POPs this is quite easy using Curve Force, the particles really adhere to the tube. But using Gas Curve Force with my smoke is just causing little wisps to get sucked in the direction of the curve rather than causing suction to the mass of the volume. Is there a better way I should be approaching this? Thanks for the advice
  13. Vector maths basics

    I'm learning a bit about basic vector maths. I'm getting a bit confused by vector direction. My understanding thus far is that a vector will always get it's direction based on its relationship to origin (i.e. draw a line between 0,0 and x,y and that's your vector direction). But then I have seen some Houdini tutorials which talk about adding one vector to the tip of the other to get a vector which has a direction which is not based on its relationship to origin, but rather to the tip of the previous point. Is this possible, and if so how is this determined, given that a vector only has the coordinates of a single point in space? Example in my attached picture of A+B, where I was told that the result would be the green vector. Though based on my understanding of vectors I would have thought this would always result in the dotted blue line.
  14. Vector maths basics

    But how would you define the direction of the green vector, because without the point of A as a reference, how are we to know by reading the green vectors coordinates that the origin is the tip of A?
  15. I'm following recommendations to avoid use of the copy stamp SOP. I have a trail effect which I've created with a solver sop which I want to copy to points on a grid, using a forEach and a CopytoPoints. But I want to vary the randomise seed of each of my trails so they appear different. How can I pass on an attribute with a unique value per point which will "stamp" the trail, allowing me to apply a unique seed to each copy? Thanks for the advice. polyextrude_solver_foreach.hiplc
  16. Copy Stamping using the new ForEach workflow

    Thanks Andr1. This is a little different to what I was proposing which was to change the actual branching of each pattern, but is interesting nonetheless. I've been trying to decipher your hip, can you elaborate a little on what you are doing by isolating the back face and applying the pivot? I'm a bit lost getting that part. Thanks for providing that example. Thanks Toadstorm. I'm surprised by this, I would have thought it would be a common technique.. I suppose it is not a very efficient way of doing things.
  17. Copy Stamping using the new ForEach workflow

    Thanks David, nice video. I am familiar with those techniques for stamping static objects. Where it is not working for me is that I'm trying to copy solvers, and use the same technique to vary a seed which randomises the pattern of each trail. However for some reason, it doesnt work, all the trails still appear the same (see project file). Do you know why this may be? Also, I noticed in your vimeo comments you replied that you weren't sure whether for each loops are more efficient than stamping. I believe that whilst there may not be much gain just comparing to for each loops, the benefit comes from being able to use for each loops inside compile blocks, which are significantly faster. Jeff Wagner talks about it here at around the 45min mark:
  18. Using a Group Expression SOP I can find the last prim of my geo with @primnum==`nprims(0)`-1 If I want that selection to change randomly between, say the last 4 prims, why does the following not work: @primnum==`nprims(0)`-rand(@Frame)*4 Also, is the reason I require backticks for the nprims expression above because it is a hscript expression in a VEX context? Thanks
  19. Rand value in Group Expression

    anim, thank you! Exactly that. I was watching the geo spreadsheet totally lost as to why the grouping wasn't moving beyond the first frame. So if I were to summarise this into a rule for my future self, Hscript expressions, which must be used in backticks to work in a VEX context, will always only return a single value. If it's not too low level to explain, why is this?
  20. Rand value in Group Expression

    Thanks guys. So what I am trying to achieve is quite simple in theory but not working for me so far, and I think I can see why... I start with a box, which I run into a solver. Inside the solver I have a very basic setup which takes the previous frame into a Group Expression which randomly selects one of the last four prims, and then a poly extrude to extrude that selected prim. So the effect should be that the end of the object grows a new extruded face each time, like a twisty branch growing. Displaying the primitive numbers, I think I can see why this isnt working. For some reason when the extrude is running through the solver, it shifts the primitive numbers around every iteration. Whereas if I were to take a box and extrude it a few times manually, all existing primitive numbers hold their original position, and 4 new numbers are created each time you extrude and create 4 new polys. Can anybody explain the logic of why this is happening inside the solver? Thanks! polyextrudesolver_project.hiplc
  21. Rand value in Group Expression

    Thanks bhouse will give this a try tonight. Regarding the backticks, symeks post just mentions backticks need to be used when writing expressions in fields which expect hscript. This is Vex input so does this also apply as a blanket rule in Vex? Symek has confused me a bit, he categorises those expressions like npoints () as being different to Hscript, Ive always thought of those expressions as being Hscript expressions.
  22. Render Cd in Packed prims

    Thank you kindly!
  23. I have a grid with random coloured points, copy a bunch of cubes onto it using a copy to points and select "pack and instance". Why do all the cubes inherit the Cd and show it in the view port, yet when I render, they do not show Cd? How can I get around this? Thanks
  24. Hi, I've been struggling to work this out for hours, wondering if somebody can put me out of my misery and give me some direction. I basically have created a simple solver setup which grows a wiggly line using an Add and randomly transforming the position of the last point on the line. I'm trying to copy this wiggly line to points using a Copy to Points and For Each loop, but can not work out how to get the randomness of the line be different for every copy. I thought maybe I could create an attribute based on the iteration value which could be used as a seed, but it's not working for me. Would really love some input on this, Thanks a lot, much appreciated Growingline_Solver.hiplc
  25. Alembic geo not working with Boolean

    It was the conversion to poly that I was missing, thanks so much.