A Couple Of Questions

[rohandalvi]

hi everyone,

I have been using Houdini on and off for about a year. It's mostly as a hobby becuase professionally I have no usage of it as such. I am in India and here most people havent even heard of the software:( . Anyways,I have a couple of questions regarding Houdini.

1. Is there anyway to view the VEX Network from a pre-existing vex builder SOP or POP. I am specifically interested in the VEX Sprinkle system in POPS. I just havent seen too may VEX examples for controlling particles and the Sprinkler system is the most complicated example I have ever seen. So I wanted to figure out how it was done. I have done a few experimentations of using VEX for POPS but nothing as complicated as the Sprinkler. So is there anyway to see the network, so i could sorta reverse engineer it. Or if anyone has a complex VEX POP example file that they could share then that would be great too.

2. What is an ATTRIBUTE. More precisely what does ATTRIBUTE CREATE do. How does Houdini understand this new attribute. I can understand that if I paint some color using a PAINT SOP then houdini creates a Cd attribute for that object, which can then be used. But when u create something brand new , like in the HOUDINI 101 DVD he created a width attribute to control the line width, How did Houdini understand it. Is there a set list of attributes that u can create or u can create anything. I am still a little lost about this area , so any explanation would be most helpful.

Thanks in advance

with regards

Rohan Dalvi

[rdg]

Hi Rohan,

1: You can view the VEX source code by RMB - Type Properties and selecting the VEX Code Tab.

It doesn't show you the network but the actual code.

You can also enter changes and "test compile" them here.

2: Attribute Create creates a new Attribute on the specified entity

This attribute can be used in a myriad of ways: eg you can write a custom shader that uses this attribute to control a visual effect like the blending of two bitmaps. If you name the attribute like an shader parameter (like clr dor the VEX Constant shader) you can control the color of the surface. I don't know how/if this works with H9 materials, though.

Hope this helps,

Georg

[rohandalvi]

hi georg,

thanks for the reply.

I know you can see the code, but that doesnt really help. I am not really a programmer, I can understand a bit but not everything ( Thats the reason I started to learn Houdini, because I can do crazy stuff with out having to write complex programs ) . I wanted to see the network because I have a fair enough understanding of the VEX network system, so I can understand that. Somehow it's easier for me to undestand the network than just seeing a thousand lines of code .

As far as attribute creation is concerned, I think I will just have to try it a lot of times to fully grasp it. What you said helps a little , but I guess only practice will make perfect.

still thanks once again,

with regards

Rohan Dalvi

P.S. If you or anybody has any kind of example file for a complex VEX based POP system, I would be really grateful to if you could share it.

[grasshopper]

Hi Rohan,

Not all VEX operators are developed in VOPs. You can write the vex code directly so the chances are there is no VOP network to look at for the VEX Sprinkler. Just by glancing at the vex code for this POP leads me to think it was coded directly as it is very 'clean'. Usually when you generate vex code automatically from VOP networks you get pretty ugly looking code even if it works! I think it is worth the effort to try to understand the vex code itself rather than just restricting yourself to VOP networks. The example you chose looks pretty manageable.

As to attributes, think of them as a quantity that you apply yourself to each point or primitive that can be used for a multitude of applications. There are some attributes that Houdini gives you 'for free' such as position. There are others that get added by various operators such as normals and colors. But you can add anything you like with an attribute create. For example, a point or primitive could store a measure - which you must provide a calculation for - of how far it is from the camera. You could use that to adjust the scale of particles as they approach the camera for example. But really attributes can store anything. As Georg says often it is useful to pass them on to shaders to control material characteristics. Understanding attributes is vital to being able to fully utilize the power of Houdini because they are so versatile! I haven't looked at it yet but there is a new demo for Attribute Transfer. That will probably give you a better understanding of what attributes can do for you. Check it out.

john

[pagefan]

A lot of the shaders are done in VEX, not really POPS but you could get the idea. There is also a tutorial on CMIVfx about programming noise in VEX. This might be a good starting point.

[rohandalvi]

thanks a lot guys.

I guess I will have to start learning how to code. It's something I have been avoiding for a while, but I guess I really dont have a choice

So one more thing. If I code something in VEX how do I compile it. Because in the Cmivfx tut, he used an inline Vex code node, it that what i use or is there some other way. Also are there any basic tuts for Vex programming. Some place to start. Also, do i need to know some programming language before I get into VEX coding?

I am still confused about the whole attribute thing, but I guess i will understand it better once I start using it practically.

But again , thanks a lot. You all are very helpful.

with regards

Rohan Dalvi

[rdg]

So one more thing. If I code something in VEX how do I compile it. [...] Also, do i need to know some programming language before I get into VEX coding?

You write the code in your favorite texteditor and save it as a vfl file.

With windows you start the "Command Line Tools" for your Houdini installation and navigate to the directory you saved the file to.

enter:

vcc -l filename.otl filename.vfl [ENTER]

this will compile the sourcecode into a Digital Asstet. Just install this to your Houdini and you are set.

Knowing some programming language would make things much easier.

You can build simple VOPs and explore their sourcecode to get a start.

Georg

[rdg]

http://www.preset.de/2007/0824/generic_ripple/

I compiled a how to make a vex operator without the command line tutorial. It's not a POP but maybe it helps

Georg

[rohandalvi]

oh wow,

thanks a lot for taking the time , this is perfect.

really grateful.

with regards

Rohan Dalvi