# Lister

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11

1. ## Cache options for geometry

I have modeled several individual bones of the skull, and I want to use Houdini during a lecture to discuss these bones. What I would like to do is set some keyframes on an exploded view node over 200 or so frames, and scrub from 0-200 to move the bones towards or away from each other during the lecture when I discuss how the individual bones fit together. Scrubbing is not an option without cacheing the animation in some way. What are my best options for cacheing, given that there are no other changes to the actual geometry of the individual bone models?
2. ## Division in VEX expression in point node

Quick question, I was watching Jeff Wagner's webinar on the changes to nodes in 16 and at the 15:04 mark he starts discussing the new Point node. In the drop down options for the VEXpression field there are a number of options, such as Pass Through, Constant Value, etc. There is a Multiply by Constant Value but no Divide by, and if I try to write a VEXpression and use a division sign it does not seem to evaluate. For instance if I wanted to create a gradient of color along a line, I would try to use set(value.r + (@ptnum/@numpt), value.g, value.b) but I would just get values of 0,0,0 for every point. I can do the @ptnum/@numpt division in a separate Attribute Create node but not in the VEXpression field of the Point node itself. Can you not use division in VEXpressions?
3. ## Division in VEX expression in point node

Brilliant, thank you, that worked out.
4. ## Copy To Points problem

I'm running into a problem with the new Copy to Points node in 16. I'm running through one of Rohan Dalvi's tutorials, the hard surface modeling one, and the step that I'm at is to copy a profile to the points of a partial circle and skin the result. The problem is that the copies of the primitive have their primitive normals facing in opposite directions depending on whether the copy is on the negative or the positive x side of the x axis, so the skin fails to produce a continuous smooth surface- at x=0, the geometry pinches. And of course the resulting geometry has some primitive normals facing in and the others facing out. I've attached a simple version of the problem. I'm not sure if this is because I can't set the Up vector in the new Point node? I'm setting it directly in an Attribute Wrangle node. Thanks in advance for any help. I'm sure it will be some simple thing that I'm missing, but I haven't opened Houdini in several months and I'm really rusty. skin_normal_problem.hiplc
5. ## Copy To Points problem

Thank you very much for the help, I don't know why I didn't think to just do that to start with- probably got too locked into following the steps of the tutorial. I'd still like to know why the facing for the primitives in the copies flipped when crossing the x axis but now I can move forward, thanks so much.
6. ## particle splitting

I'm a novice user, trying to figure out how to split particles exponentially- start with 1, splits into 2, splits into 4, etc. I figured I'd try the POP replicate node, but the problem I'm getting is that I can't figure out how to get the new particles to feed back in and be a source for another replication. I imagine this is something easy to solve, I just don't know how to use this node at all, can anyone suggest something for me to try? Should I be trying to use some kind of For loop?
7. ## particle splitting

For some reason I never got the alert that someone had responded- thank you very much, I'll check this out later tonight (and probably end up posting again with a new question!).
8. ## Problem with undefined variable

I'm having a problem with a tutorial I'm doing. Since it's a paid tutorial, I don't feel comfortable posting my file, so instead I'm going to post a screenshot, which hopefully will be enough, but if it isn't I'll figure out a way to get something else posted. In the tutorial, I'm putting a simple animation on a cube, which is in the nodes to the left in my screenshot. I then copy the animated cube onto a grid of points, but only at the points that are colored red, which is also controlled by an animation with an attribute transfer, which is the node tree on the right. The tutorial uses a chop net, which is something that I have zero experience with, so it could be the problem is there but I don't think so. The problem I'm encountering is that after 1) creating an attribute called crf, and 2) storing the frame that the animation for each cube beings on as the value for crf, 3) I create a stamp variable with the name crf that uses the stored value for \$crf and I get an error that 4) \$crf is undefined. I don't know enough about how Houdini creates and stores variables to troubleshoot this. I don't know if it's a problem with using crf as the name in the attribute create node, and then again in the stamp variable, or what. When I look at the geometry spreadsheet at the group node, everything looks fine- the expected crf values are listed for each point. The bigger problem is that I can open the supplied file from the tutorial author and it works fine there, even though by my best inspection the nodes are all identical between the source file and my attempt to recreate it. One thing that could be an issue I suppose is that I'm up to date with my Houdini build and the tutorial file was likely made with a previous file, but I'm not enough of a Houdini user to know what has changed between versions. Am I missing something obvious about variables that I should have done (or not done)? Thanks in advance for any help.
9. ## Problem with undefined variable

All I had to do was check on the box, thanks so much. I feel pretty stupid for missing that.
10. ## How to model cellular division?

I have a very naive, newbie question. I'm not a CG artist but have dabbled with tools over the years in helping me illustrate biology (I'm a scientist). I looked at Houdini years ago but ended up going with softimage, and after autodesk killed it this past year I've decided to put my eggs in the Sidefx basket. I'm comfortable with making static models, but in my new job I want to produce some animations of biological processes like embryological development. Since embryology proceeds by cellular division, I need to figure out how to show one object dividing into two, and on and on; you can see what I'm talking about at the beginning of the film Prometheus when the title first appears (after the tall alien consumes the biological agent that erodes his body, dumping him into the waterfall). But to make things more complicated, i would want to be able to control the generation of new cells so that the population follows a particular form- instead of an expanding ball made up of more and more cells, I would need the new cells to follow a plane or fill an irregular volume. I know nothing about animation or effects, since up until now I've only ever had a need to model a solid, unchanging object. I'm not asking anyone to do any work for me, I just need to know what methods I should start learning so I know what kinds of tutorials to search for. In short I lack the vocabulary to even begin to figure out what I need to know. I wasn't even sure if this question would be better suited to the "Animation" subforum or the "Effects" subforum, so anything that would point me in the right direction, no matter how small, would be greatly appreciated.
11. ## How to model cellular division?

Thank you for the replies, those venation techniques aren't quite what I'm looking for but eventually I'm going to want to model vasculature so they will come in handy (as will anything I pick up while I sort through them). I used a VDB node during a modeling tutorial so at least I know they exist and ought to be a good starting point. And yes, I have a huge amount of learning to do!
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