k2p8

primintrinsic transform is a matrix3. You binded it as a matrix which is matrix4 in houdini by default. Just write matrix3 m3 = primintrinsic(1, "transform", pt); instead of matrix m3 = primintrinsic(1, "transform", pt);

Hi all :), I am trying to load two sequences of vdbs on my disk, for example : cluster0.$F4.vdb cluster1.$F4.vdb with a geometry import in a top network but it does not work so far. I have tryed to load them with the filerange / filepattern node and partition them into 2 work items, cluster0 and cluster1, but i got all frames at once or nothing in the geometry import. I also tryed to create a @path attribut with a $F4 but the top network does not seem to update the frames so i only have the first frame of each cluster.

If you unlock the popadvect node you will find a popvop inside. You can acces inputs in there and modify the popvop to match your desired effect.

There is a game tool that does it. You can bake/render slice of your volume. It works for any kind of data on your volume. https://www.sidefx.com/tutorials/channel-packing-pyro-data-using-the-texture-sheets-rop/?collection=50

Hi folks ! A tutorial about recursive backtracker in vex to create mazes. The idea is simple : You get your adjacent neighbours and check if they are not visited, if not, you randomly choose one and move to it. If no valid neighbours, you backtrack the stack of your previous positions and check if there is a valid neighbour until you find one. If the stack is empty no valid cells are left so the maze is done. recursive_backtracking_001.hiplc

Hi folks ! I am cooking a pdg network, simple setup. I just split a cache by a @cluster attribut to save each cluster independantly and run a pdg over that. But i randomly have an error i don't understand : '__pdg_preframe' is invalid or already exists' Do someone know what does it mean ?

May be you can compute a vector field with a direction along the tube and some noises to create point trails procedural_roots_000.hiplc

Hi all ! I did a simple vex scene with particules orbiting an object. The main challenge is to avoid particules to exit their orbit by computing an vector that correct their distance to the surface object from an iso value. Hope you like it. Update : Added the gradient of geodesic distance as axis of rotation for the particules. Usefull if you want to rotate along each element of a geometry, like arms, legs, tentacles, etc. pop_orbit_001_odforce.hiplc

Hi all I am posting a simple procedural desintegration that is very fun to build, as always, with quaternions and vex. Vex is annoted, Hope you will like it. There is a line in vex where i remap a random quaternion [0, 1] to [-0.7, 0.7]. It roughly removes the random overlapped orientations. If you disable it you can see that orientations are a bit biased because of the 0 - 1 range. Update : Now with RBDs lego_desintegration_RBD_001.hiplc

if you are a fan of quaternions and matrices you can do a spherical interpolation (slerp) of 2 quaternions which represent the local orient of the leaf and the global orientation to the sun orient_leaf.hiplc

Hi @eunchae, The basic principle of an upres is to make a new simulation with a pre-existing velocity grid that you use to drive a new dye (density / temperature). Your new simulation should have smaller voxels and parameters close to the lowres (like temperature diffusion, flame amount, time step) if you want this new version to be close to the lowres. You then copy the lowres velocity and simply advect the upres by it. This way you only perform heavy computation like divergent free velocity (ensure the conservation of the mass of the fluid) and the boundary collision on the lowres, the upres solver only has an advect for the density / temperature / ect. all other nodes relative to velocity enforcement / computation are deseabled which allow you to quiclky compute the upres and skip all the heavy parts. Then you can add a little amount of noise with an add operation to the copyed lowres velocity to give more details to your upres. This small amount is almost divergent free on a large scale so it should not be a problem. You can add any forces at this process in the upres, but, the divergent free velocity node being desabled, only already divergent free forces should be added. Otherwise your smoke will compress into itself. And you should only add forces that do not push your upres smoke to far from the lowres, since you simply copy the lowres velocity, no new velocity will be computed outside of this bounds. So, for example, adding a wind, which is divergent free, is not a good option since your smoke will crash into the bounds of the lowres. There is some parameters that do not scale well with the upres, usually it is all parameters or operations that need neighbours voxels to be performed, like temperature diffusion. Since you change the size of the voxels, those operations have an overall result which is generaly not the same as the lowres. You could correct that by sampling the lowres version of the simulation and modify the output value, but you lose a lot of details by doing so. So in this case, it is better to slightly twik the upres simulation to perform better, by increasing or reducing the corresponding parameters.

ACES pipeline is sometimes applying slight tone mapping before the output which they call RRT (Reference Rendering Transform), and then, your output transform sRGB / Rec.709 is applyed. So you can have slightly different outputs if you are using Utility - sRGB - Texture or output_sRGB or Output - sRGB. I don't know exactly all the slight differences between all those transforms but i dont think sRGB - Texture is a usefull transform to export your pictures. This is in the Arnold ROP. You must choose your render color space (Properties > Device > Color management ) and render output (Properties > Output > Color Space) in the Arnold Rop to know which color space is used. Theoricly if you want to use ACEScg it should be ACES : ACEScg for the render engine and a linear sRGB / ACEScg for the output then you will need to convert this linear ACEScg/sRGB to an sRGB space with an gamma 2.2 or sRGB / Rec.709 transfert function applyed to be able to display the picture on a sRGB Monitor. If you want some docs about ACES there is this articles which is a good start and the ACEScentral forum : https://chrisbrejon.com/cg-cinematography/chapter-1-5-academy-color-encoding-system-aces/ https://community.acescentral.com/ PS : And Of course you must install OCIO to manage all those color spaces / transform PS2 : If you are using Arnold be sure to convert your tx and houdini color node to the correct space. If you are using ACEScg and you generate TX textures they will have a ACEScg space applyed so you can't use them for sRGB anymore and the opposite is true too. Same thing for color node in houdini, if you enter a (1,0,0) it will be for sRGB so you need to convert your color node to an ACEScg with an OCIO transform other wise you are not sending the correct color to Arnold.

Hi folks ! Is ACEScg rendering usefull for volume rendering ? I was reading more about ACEScg in general (still abstract for me at this point) : https://chrisbrejon.com/cg-cinematography/chapter-1-5-academy-color-encoding-system-aces/ And it seems, from the article, to give good results in color saturation and GI so i am planning to implement aces in htoa to do some tests. Have you guys already tested ACEScg in houdini, especially for volumes ?

if you want to know more about bullet constraints themselves there is Tokeru website : https://www.tokeru.com/cgwiki/index.php?title=ConstraintNetworks he explains in details attributs on prim / points with examples

@Atom What does it means 'in other DDC packages' ? If you want to match a pyro look to an other pyro you can look at the volvis_ attributs created by the post process of the pyro. You will need density / flame / temperature fields and the values of the ambiant / reference temperatures in kelvin of the pyro solver. If you match all those values you should have an identical result. If you re importing smokes simulations from an other software you might need to fitrange / scale the fields first i think.