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Found 23 results

1. ## VEX - Variables/attributs in vectors

Hi all ! I'm struggling with an addpoint function, I'd like to use a variable to declare a point but it seems that's not allowed… What is the proper way to do this ? My code in a pointwrangle : float height = fit(rand(@seed, @ptnum), 0, 1, 0.4, 0.55); addpoint(0, {0,height,0}); if I put a 1 instead of "height" it creates the point perfectly well :/ Thank you for your help !
2. ## Signed angle between vectors in VEX

In Vex, I'm trying to find a signed angle between two vectors i.e. an angle which treats one vector as a "base" and the other as a rotating "clock hand", so that I get positive angle for a concave angle between the two (0-180 deg) and a negative angle for a convex angle between the two (180-360 deg). The dot product on normalized vectors gives me the angle, but it's symmetric. Is there a trick that gets me the sign?
3. ## random normal direction

I'm trying to control the normal of a single point. I want to use normals to visualize vectors that i will convert to velocity later. I've reduced my experiment to a single point to hopefully simplify things. I'm trying to make the normal point in a truly random direction for each frame. I tried this: float x = fit01(rand(ch("seed1")),-1,1); float y = fit01(rand(ch("seed2")),-1,1); float z = fit01(rand(ch("seed3")),-1,1); @N = set(x,y,z); which gave me a random direction with in a disk. If i substitute @N for @v and feed this into a popnet that uses inherited vel i get particles in a plane. see attached image. If I control each component of the vector leaving two at 0 and setting the third between -1 and 1 i can point the normal in any direction. I can't figure out how to get houdini to randomly set the normals direction in all directions. Help appreciated.
4. ## (Novice) Align a selection to point

Very simple operation required: I need to align all points to the vertical axis occupied by a single point. (align points to the vertical axis of the point highlighted) There has to be a simple method for this. Thanks in advance
5. ## Motion Vector of projected Shadows of moving object

Hello!, Let's say I have a rotating cube, a grid floor and a direct light projecting the shadow of the cube into the floor.. how can I get the motion vector of this projected shadow? , I already know how to get the vectors of the cube but it's shadow is a mistery.
6. ## How would you get the index value of a vector array from another point?

Hello, Trying to read a vector array from another point at a certain index. From my understanding of Houdini something like this should work. vector tempArray[] = point(0,"vectorArrayAttrib",pointToReadFrom); vector v = tempArray[index]; Unfortunately this method is returning an empty array from the point() function. If this is not the right way to go about doing this please let me know. Any help welcomed. Thanks.

Hello,I'm attempting to create the slitscan/timeshift effect. I'm creating a vector array in a for loop, each loop has an attrib from map and a wrangle that appends Cd to a vector array. It works when the attrib from map is always reading from the same file. When I change the attrib from map file read expression to anything that has to do with \$F or the meta nodes iteration Houdini crashes. I have a test scene that has documentation and even nodes setup to create test frames to work with.If it is a matter of the way that multiple files cannot be read at once please let me know. If someone knows of a better way to read from multiple files at once and/or achieve this effect please let me know. I'm aware that after effects has this effect and uses gradients to determine which frame to look up color from. While that method is great, I'd like to be able to write the gradients/lookups in vex to achieve results. Any help greatly appreciated. -T concept_025_slitScan_v001.hiplc
8. ## retarget or recompute vector

Hi everyone, I try to figure out how to retarget a vector (v in that case) in particle trails. I explain: i got master particles who trail other particles in space, i inherit the master "v" to achieve a motion blur at render time, to avoid to much substep that way i got smooth line at low calculation cost. but i need to slightly noise the trails to achieve a "moving tentacles" look. Here is the problem when i apply the noise, obviously my "fake" v vector is not aligned anymore, it's stepped... i tried to recompute the vector with the help of id, but since my emission is not constant ( i shot on frame 5, frame10, frame15 etc..)the incrementation of the id in not constant to...I tried basic vector arithmetic, but i don't get results i need...I join a hip file, does anyone got an idea??? thanks by advance. Best H PS:excuse my english, I'm French... RecomputVelTest.hip
9. ## Object facing vector

Hi So basically I have a vector and an obj, how can I make the obj face the vector by specifiyng the front axis of the obj? (front, side, up) Is there a traditional way to do this? Because Im trying to do this myself through Vex and some transforming operations.. Example:
10. ## Vector component in stamp expression

Is it possible to access a single component of a vector in a stamp expression? Or is it just limited to single numbers? I've searched and haven't found anything specific to copy stamping and vectors. For example, if I had a vector attribute called size and I wanted to just get the second component. I've tried: stamp('../copy1', 'size.y', 0) stamp('../copy1', 'sizey', 0) stamp('../copy1', 'size[1]', 0) I know it would be easy enough to create an extra attribute with just the second component to stamp instead. But it seems like this should be unnecessary.
11. ## houdini vector, tutorial, motion blur, alembic, maya, arnold, fusion, abc, fluid, workflow, nuke NEW TUTORIAL! Alembic Vector Motion Blur

NEW TUTORIAL: Alembic Vector Motion Blur Tutorial- A Houdini, Maya, Arnold and Fusion or Nuke Workflow Thanks for watching and Sharing! If you have any suggestion, please come them in! Thanks
12. ## Whitewater workflow for Maya

Hello, I think I've just blown my head trying to figure out a solution for this but I hope you can help me I made a simulation of water and whitewater in Houdini and then used alembic to send the mesh to Maya for rendering. The whitewater particles were sent via the Realflow connectivity plugin in .bin format. Maya had no problem opening both the water mesh and the whitewater particles, but my problem is that Maya can't compute any motion blur, I think this is because the files I exported do not have any motion vector information in them. Is there any way I can export this information and use it in Maya? To export the water mesh, I created the simulation and then I exported it to .bgeo sequence from the import node, then I re imported the .bgeo sequence in a new geometry file and created the mesh using the "particle fluid surface node" and from there I connected a ROP alembic output node. To export the white water I got into the whitewater source node and in that level I created the RF Particle Export node and in it's properties I referenced whitewatersource.cache in the SOP Path Also, I saw a video where v-ray proxy import is used to generate motion blur with some realflow mesh with the same problem, I don't know if I can do the same in Arnold, which is what I'm using for rendering. I'm quite new to the software but I'm loving it, if you can help me I'll appreciate it. Thanks.
13. ## Motion Vector Pass h14

Hey, I have time seeking any motion vector pass somewhere in odforce, nothing work as fine for now, so any know the method of get motion vector pass from mantra pbr using all scene animation as alembic, camera moving, etc with houdini 14 ? thanks in advance Carlos
14. ## Arnold Volume + Motion Vectors

Hi I'm actually trying to export a motion vectors pass with arnold for a pyro simulation baked into a VDB. I understand the concept behind the theory, which consist of getting pyro velocity matrix, camera inverted matrix, and multiplying them, but till now, I can't get to make it work. There's an example involving Mantra who work quite well : http://forums.odforce.net/topic/14831-motion-vector-for-volume/?hl=%2Bvolume+%2Bmotion+%2Bvector+%2Bpass The problem with this example is that the nodes used (GetBlurP) doesn't have their equivalent in the Arnold shader. I'm pretty sure I can do it with user data passed to the shader, but I can't figure it out. Does anyone here have ever achieved this? I would be very happy to hear about. Thanks Maxime
15. ## Copy SOP and Rotations

Hi everyone. I'm hoping one of you clever people will be able to help me with this little problem I'm having. When copy-stamping objects onto some animated points, the copied objects are transformed along with the points, but they do not fully respect the rotations. I have a feeling the solution will require a vopsop, with some kind of vector math to get Y normal rotations, but my knowledge of vector math is very limited and I'm struggling to find an elegant solution. I've created a simple scene to demonstrate the issue. You'll see that the teapots do not rotate along with the grid that they are copied onto. Any help would be much appreciated! rotNotWorking.hip
16. ## VEX supports array function?

Hi, this is my first post here. I've been trying to call a vector array function in VEX, but it either returned "Internal Compiler Error" or "Syntax error, unexpected identifier, expecting ';'". I also checked Array help file and the example as below didn't work at all: To specify a literal array, use curly braces, with the array members separated by commas: vector[] rgb_array() { return { {1, , }, {, 1, }, {, , 1} }; } Here is the simple code I tried to compile, but it returned an error message "Syntax error, unexpected identifier, expecting ';'." vector an_array[] = {{1,1,1}, {2,2,2}}; vector a[]; vector[] testFunction(vector[] a){ return a; } a=testFunction[an_array]; Does anyone know if VEX supports array function? Thank you very much!
17. ## refract() vex node, breakdown

Hey Guys! I've been experimenting with the refract node in vopsop context as well as the refract() function in vex. I'm curious if anyone has been able to break that node down to it's raw form? I would essentially like to know how it actually evaluates it's inputs. Can anyone shed some light on that? I would like to know the math behind it. The refract function takes three inputs, a direction vector, a normalized normal and an index of refraction. thanks!
18. ## Orient, rot, N + up, v etc: Instance rotation question

Hello! I am currently trying to wrap my head around being able to transform (rotate) instance objects for sop copy and instance rendering. Basic stuff, I know, but I'm stuck and my math suck. I have a hard time grasping dot product, cross product, matrices and quaternions -> 3D transforms There are, as far as I can see, a multitude of attributes and options to do this, and I am wondering what would be best suited for my use? Some use up, some use orient. Basically, I would like to have the rotation options of the transform sop (x, y, z rotate) to work on a point instance where the normal direction is the "up" direction (think teapots standing on a displaced ground plane, rotating planar to the ground when editing the y axis). I've been through a lot of examples but I just can't make them work for my scene. Either the objects are flipped or rotation is happening on the wrong axis or objects are not rotating smoothly, or I am not able to figure out how to "flip" to the right axis when using N and up (usually +-90 degrees in x) inside the vop. Most of all, it needs to be stable on deforming geometry. Any example of rotation working in this scenario would be most welcome! Also, if you have a link to a good (basic level) resource regarding this topic, that would be awesome! Thanks.
19. ## how to render correct 2d motion vector for Fur object

I learn that 2d motion vector Nuke use is different from RSMB, it is something like projection, for example, I have a point move from posA to posB during 1 frame, so project the point use ray from real world to camera screen like the picture below, so it is different, I want to know how to write this shader? And the image below is what I search in forum, this is wrong when I render 2d motion vector for my fur object. Now I want to render read 2D motion vector for my fur layer, anyone know? Thanks a lot.
20. ## Identifying the same point attribute

Hi, how would you identify points which share the same position (or vector/attribute) and group/tag them? There is no specific amount of points sharing the same position, could be any. Thanks
21. ## vdb - create fields

Hello, I am playing around with the VDB stuff lately and most of it works great. But I noticed that i can't use a plain VDB node and create based on the dimension source a volume, like a velocity field. It always said "<empty>". I like to create a vector field and then manipulate it by the Volume Vop as with the standard Houdini Volumes. Any tips or a workflow explanation would be great. Thanks nap vdb_empty.hipnc.hip
22. ## save point position data across frames in sop solver

I am trying to create AI behaviour in the sop solver. I am able to update behaviours by using the prev frame data without any trouble. The problem is for one particular behaviour I need to save the position of certain points across a frame range, and use this data to drive the other points in the simulation. The solutions I could think of were: I tried using a pop network outside of the sop solver to birth new particles and access these points back in the sop solver. But the solver errors out if i connect the data from the pop network into the solver tree. I guess this is because i am making new points outside of the solver. I also tried to create new points using python and the `add` sop. this is terribly slow and almost brings the whole thing to a stop. The most obvious solution seemed to be to create a list attribute in python and save the data into it. But if i do this in the sop solver then the data gets overwritten per frame. Is there some way to create an attribute that could store an array or list of position data across frames. From the documentation i understand that only floats, int and vectors can be used as attributes. I could just append the new position data to this list per frame and access it later in the tree. Thanks ---------------------------------------------------------------------------- www.vimeo.com/tusk3d
23. ## angle between bones

Hello I am making some simple rigg and I want to measure angle between two bones. I used vector node in chop network but it is not working for me. When I plug boxes/nulls it works pretty well. I am sure it is something with nature of bones. I found some tricks to achieve my goal, but I wonder if there is some simple method to measure angle between two bones.
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