# draxysd

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9

1. ## implicit uv problem

Hi guys, I have a bit of a mindbender. My idea was to make a complete line trail from a point, make some attributes on the line and then carve that line to emit particles behind an object (reading the percentage attribute off the points). I went ahead and computed percent along the path for each point on the line. Except that when I use that percentage in a primuv expression, it does not align with the point. Here is the vex code (run in detail mode in a wrangle node) used to calculate percentage along the path: float perimeter = prim(0,"perimeter",0); float len = 0; for (int i=0; i<(@numpt-1); i++){ len += float(length(vector(point(0,"P",i+1))-vector(point(0,"P",i)))); setpointattrib(0,"perc",i+1,len/perimeter); } @totallen = len; the last bit is just to check if my aggregated length is the same as the measure sop length (which it is). As you can see in the attached HIP file, the point follows the line, but diverges from the original point positions (which is the whole point of the setup). Hope it is something very obvious I'm missing and you guys can point me in the right direction. primuv_problem.hipnc
2. ## implicit uv problem

Okay, found a workaround (as it usually happens, within seconds of asking other people :). I used a xyzdist to transfer the implicit uv to the points instead of calculating the procentage. If somebody can explain why the implicit u coordinate differs from calculated percentage that much, I would be very thankful. Might save me some headache in the future. P.S. for anybody interested, here is the wrangle code used to get the u coordinate: int prim; vector uv; xyzdist(0,@P,prim,uv,100); @perc = uv[0];
3. ## Scaling force influence based on particle age

Hi everybody, I want to have a bit of control over my simulations (in this case flip, but it would be good to have a general dop workflow). I want to be able to apply a force based on my particle age (or in general based on a point attribute). What would be the best way to do this? I was thinking of fiddling with popwrangle. If this is the right way, do I affect the velocity or some other attribute of the points? Thanks in advance
4. ## Scaling force influence based on particle age

Thanks for your reply James, very insightful stuff. How about affecting standard dop forces on a per point basis. One thing that comes to mind as a workaround is to make a volume from the attribute on each frame in SOP solver and use that as a mask for the DOP Force. Not as precise but if you don't have much particle interpenetration, should work. I just have to wrap my head around how to build this.
5. ## Sweeping points to polygons

Hi, I have a little problem. I am making a curve sweep in houdini. My setup is to scatter points on a thin plane, noise it, then animate that along a path. I objectmerge that into a new object make a trail in sop solver and mesh everything in vdbfromparticles. I'm kind of starting to hit the vdb resolution limits (it is starting to take way too long to compute). Is there a way to sweep a noised line (ideally just noised points) and make a ribbon out of that. What I want is something like a sweep but to be able to manipulate the points that make the line during time with wrangle nodes. Basically, I would just like to get a polygon strip that I can texture as oposed to the full vdb meshing (I have uvs on my vdb, it's just a little slugish and the interpolation screws up some areas) Cheers.
6. ## prt export from Houdini 12

Thank you very much. Before I had to have H13 vc9 for prt output. This simplifies the workflow considerably Thanks a million
7. ## Fluid Source SOP, noise problem

Any of you have a problem when turning on the noise in the Scalar Volumes tab of the Fluid Source SOP. My particles disappear as soon as I tick the check box "Use Noise". It has been so for a few versions now, and it is starting to get annoying. Thanks.
8. ## Fluid Source SOP, noise problem

Thanks for the quick reply Cheers
9. ## H12.1 FLIP sim changes with resolution

@old school Hi, was just wondering if you can point me in the right direction regarding the @name= syntax. It is the first time I have seen it, and although I can imagine what this command is specifically doing, I would like to know where in the help docs is this topic covered. Thanks
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