Hi,

I've been working on fracturing and controlling where fracturing is active and had someone help me get this working in Houdini 15.

I was watching a tutorial over on Digital Tutors about Controlling Your Fractures in Houdini and it was done in an earlier version.

What I did in the node where my fractured object lives is do an attribute transfer of color to denote which fractured pieces I wanted to remain inactive.

Anyway, this code was in the PopWrangle node.

The SOP path is: /obj/vase/OUT_ACTIVE_PASSIVE
Which I get. That's letting the PopWrangle node know what to look at.

It's this code that I'm wondering about, but mostly the first line.
vector Cd = point(@OpInput1, “Cd”, @ptnum );

This line I get, except the syntax of the i@. Not sure what that is, but I understand that this is setting the active to either 1 or 0 based on the color which I set to black or white on the attribute transfer.
i@active = int(Cd.x);

I come from a programming background. JavaScript, Actionscript and going way back, Pascal, Basic and should I even say Cobol (that was in college though) so I get scripting and syntax and logic.

Just trying to grasp how it works in Houdini.

Thanks,

Jim

the i@ is declaring a new integer attribute on the geometry, v@foo creates a vector attribute etc…


when you use int foo or vector foo, it creates it as a local var to the current code

vector Cd = point(@OpInput1, “Cd”, @ptnum );
for this line, the point function is looking to the second input, inputs are 0 based, and getting the color attribute for the current point number in the first input, @ptnum


does that make sense?

OK, that does make sense, thanks.

I'm just curious why it needs to look at OpInput1 instead of OpInput0?

So @ptnum is the current point number, I get that.

What I'm trying to ‘wrap’ my head around is that a node ‘loops’ through all the points or whatever and applies it to ALL the points without me having to manually to a for loop in standard programming.

In the ‘old’ days, I would write a for loop and loop through an array.

Also, is there some documentation on what attributes are available for points intrinsically, and I'm assuming I can create my own attributes.

Hopefully I can understand the OpInput0 and 1 stuff so I know WHICH input to look at.

Thanks for the explanation.

Jim

you can now use 0,1,2,3 instead of @opinput1 …that makes more sense to my brain as well

v@Cd = point(1, “Cd”, @ptnum); to get from the second input,

if you want the Cd value from the first input it is more common to just use

vector myColor = @Cd; and avoid the point function lookup

the vex code actually, and I may need correction from the devs on this, but I understand it to execute on all the points at once, in threads, rather than a typical for loop from point 0 to point-n

you can write standard flow control statements as well, but those would also execute per point/entity type


creating your own attributes is as easy as using the @ syntax instead of just the type label