Hi all. Continuing on with my struggle to learn this beast, I have come upon a confusing issue. What are VOP used for and how? Heres my confusion. In SHOP I add a Light shader node. Then in Objects, I specify a light to use that particuar SHOP as light shader. Now in VOP there is a Light Shader VEX node. But I can't hook this light shader in Objects as it is not offered as an option in the pulldown in Light parameters like SHOPs. So what are VEX used for and how. Also how are VEX's different from SHOP. I see that in SHOP I can create shaders, but also in VEX. OK but I am not able to apply VEX shaders as materials. Simply I am not able to find the node in SHOP and in SOP that sas “Use this VEX as shader” or something like that. Its probably there, or I have use multiple nodes in some way. But the point is, its not apparent and it really should be. Its unneccessarily overcokplex. The area of overall connectivity is where Houdini tutorials come up short, perhaps thats intentional. They way its setup is very very confusing with no apparent logic. How is a CHOP used and where? How is COP used as , anything, in other parts of the app, a displacement texture in a disp SHOP. Interconnectivity, that kind of stuff. Honestly, with no malice towards SideEffects, I rate tutorials on CD as poor to fair. Simply they do not explain what needs to be explained, which not just what a particular node does, but how the whole application ties together. They frequently leave out important details, like into which slot a connection should be made. The PDF documentation, is likewise defficient. The explanations don't make sence, at least to me. The POP tutorials are really bad, as they describe the function codes to enter but there is little explanation as to what the codes do, and there is no syntax list with descriptions. I did the spaceship POP tut two times, and I still do not understand what goes in on POP nodes, and why there are Point nodes in SOP. I get that Point node reshuffles the vertex order but little beyond that.

Dave Rindner

Umm……..

ok… here we go….

SHOP, is also known as Shader Operators. SHOP is almost like a library of shaders. It is a place where you store all your already created/compiled shaders - like a book it is already written by the author. In SHOP, you don't really mix and match shaders as you would with other OPs. In order to apply those shaders into your geometry, you will need to use Shader SOP to bring those shaders from SHOP into it.

VOPs, also known as VEX (or Vector EXpression) OPerators. VOPs, is essentially a shader builder. That is why there is a desktop called “VEX Builder”. VOPs will build shaders that can be stored in the SHOPs editor, in which you can bring your custom shader into your geometry. In the past, people have to use a text editor to write those shaders out by hand. But with 5.5, SideFX build the GUI for it so that many of us who don't code may use the visual interface to create our own shaders. However, I will tell you right out that VOP/VEX are advanced for beginners and that it is good to understand VEX language first.

In short, VOPs is used to create shaders. SHOPs is a library that store shaders. And only from the library can you check out a book (a.k.a “shaders”).


CHOPs, is also know as CHannel OPerators. This piece of tool is just extremely awesome for animators once you understood how to harness its awesome power. IMHO, Maya's TRAX editor is nothing compare to what CHOPs can do. (I can't say anything about XSI's Animation Mixer as I never used them).

CHOPs is basically where you can use it to drive/automate your secondary motion in SOPs, POPs, COPs, OBjects, etc as well as many other things. You can even use it to build your interactive animation in which your MIDI, keyboard, mouse, and other input to drive the interactive animation in real time; keyframe-mixing; motion capture editing; motion compositing(!!); IK/FK switching; oh heck, you can even animate your animation curves and then export them back to your models. What's so special about all CHOPs is the fact that your original keyframe motion curve is still there while you're editing your motion curves. It's totally non-destructive and non-linear.

You mean stuff like what $PT, $LIFE, $AGE stuff does? They are pretty much self-explanatory already on a lot of case. The documentation did explain what it does. (Particle Manual; pg 9 - 11) as well as the Expression Language manual.

I will agree with you to certain extent that the manual is a bit lacking in other areas.

as far as the space ship tutorial goes, I am writing this from memory. The reason they have to Point SOP there is to set teh point normals. This point normals can be used as a direction that tells the particles where to go.

Essentially, Point SOP are the swift army knife in the world of visual effects. What you can do with it is sheer amazing! For crying out loud, I even learned from Jason Iversen (Digital Domain) that you can even use the mathematical dot product to calculate surface diffusion via Point SOPs.


Cheers,
ALex

LAex. Thank you. THat helps a little, but I am still confused as to the exact procedure. How is VEX shader brought into SHOP? Detailes please.
How is a VEX shader applied to geometry? Its those how to details that I am unable to peice together.

Dave Rindner

Hi there David,


There should be a tutorial video on your Learn CD concerning how to bring the VOP shader into SHOP in a few different ways. One of the quick way that I often do is by RMB on a particular VOP tile (a.k.a VOPNET) and choose “Create New SHOP”. Now in your SHOP, you'll see a new VEX shader been created. There are still other ways which you can do it. Such as via “Export optype” and such depending on what kind of pipeline you want.

When you first go to your VEX Builder desktop (Which is the VOPNET at the moment) and lay down a VOP tile - let's say “Surface VOP” for example sake - that Surface VOP will be the Surface VEX Shader, but it has nothing inside it yet because the shader has not been built. Now you can Alt-LMB or hit Enter to go inside the VOPNET. Once inside is where you will be starting to connect tiles to create your own custom shaders.

Please do look through those VOP video tutorial for example.

I strongly recommand you to read the VOP Manual at least. It's very advanced if you have no RenderMan shader writing experience or programming experience. I am still learning it as well, so I probably won't be able to help out as much in this area.


Cheers,
ALex

Bingo! Thank you Alex, thank you very much. As far as VEX build nodes (you call them tiles), Houdinie's implementation is similar to DarkTree and GenShade. Although experementation is the order of day with node systems, the way I learned it is by colors. Like others, Houdini color codes input/output. You can only connect inputs/outputs of same color. You probably know that. I am sure there is a utility node that converts from one type to another. So you can pipe a displacement noise and output a grayscale value or vice-versa.

Dave Rindner

CHOPs is basically where you can use it to drive/automate your secondary motion …… What's so special about all CHOPs is the fact that your original keyframe motion curve is still there while you're editing your motion curves. It's totally non-destructive and non-linear.

—-

Thanks for the overview Alex - I've been learning Houdini for about a week (hehe newbie city) and am pretty confident with the interface but am struggling a bit with understanding CHOPs… the tutorials are a bit lacking in expaining why things are done the way they are - having said that i havn't been able to do them all yet ‘cause a few r missing

in Maya i could setup custom sliders for attributes of a character quite easily, and mix their animation for nearly unlimited deformation effects… this is kinda a seperate issue from Trax or CHOPs but i’m still looking for the Houdini equivalent… i can make custom panels but i can't keyframe those which makes 'em useless… i heard something about being able to make a custom panel through VEX but i was hoping there was more of a GUI method…

anyway thanks again and if anyone has any tips or links to CHOPs resources feel free to e-mail me.

cheers

-paul
paul@renderspace.com

OK thanx for CHOP stuff. To me its more like chop sue. OK I think I get what CHOPs do, what I don;t get is how to get them to do it. How do I assign a particular CHOP to a motion F-Curve. See I thought that CHOPs are motion curves.
Heres an example.
Single Geometry (a sphere) that has a Y-axis F-Curve. Now lets say I add a noise CHOP tile. How do I get that noisy motion to overlay on top of existing Y-axis motion of the ball. What is the actual procedure?
I said it before, and PDF are not helping. I am having trouble actually understanding how all these separate parts of the app tie together.

Dave Rindner

For custom sliders, the best method by far in H5.5 is to use custom op types. See the character section in the “Tutorial & User Guide” from the Houdini help menu. On a related thread, you might also want to check out:
http://odforce.net/forum/index.php?act=ST&f=15&t=172&s=49237d6b57d3bfdebca3d73975a3fc1e [odforce.net]

In the past, people have created buttons in custom panels which performed scripting commands (chcommit) on all the required parameters. Often times, you would want to key the entire pose anyways so for those, you would only need to create one of these key buttons for most of the custom panel.

My favourite method to get a chops track to override a parameter is to bring up an un-tied floating pane of the chop viewer and then drag & drop the name of the track onto the parameter which I want to override.

>>

edward
For custom sliders, the best method by far in H5.5 is >>to use custom op types. See the character section in the “Tutorial & >>User Guide” from the Houdini help menu.

thanks for the tip - i have 5.5 Apprentice at home so i'll check it out there. i've begun modelling my first creature (in 5.046), and all i can say is i wish it was more ‘viewer oriented’ with regards to manipulating points on curves etc. i much rather prefer the visual approach of Maya when it comes to modelling, but i'll keep exploring the nodes (hehe oops i mean OPs and see what i can come up with.

cheers
-paul

cipher
i've begun modelling my first creature (in 5.046), and all i can say is i wish it was more ‘viewer oriented’ with regards to manipulating points on curves etc. i much rather prefer the visual approach of Maya when it comes to modelling, but i'll keep exploring the nodes (hehe oops i mean OPs and see what i can come up with.

Which SOP(s) are you using to “manipulate points on curves” ? All the ones which I can think of off the top of my head have handles on them and so are very ‘viewer oriented’.