Why does Switch not see my attribute?

[jfrancis]

Hi,

New Houdini user here. So far so good, except for a little confusion here and there.

For example:

I am trying to do things based on a user-defined attribute I call the magnetic 'charge,' (0 or 1) of objects. At the moment I don't want to do anything too fancy - just change colors based on charge, Later I'll need to get more elaborate.

I have a sphere.

It has a new attribute called 'charge,' which is a detail integer attribute created by using $FF and noise to produce an integer that randomly flips between 0 and 1.

The color nodes see the $CHARGE variable

But when I try to use it in an expression in the swith the $CHARGE variable is undefined.

Any idea why?

[Macha]

Uhm...first of all I'd say use a detail attribute. But even then, the switch sop does not accept it directly as $ATT, you need a detail() expression. But even then this is not a very clean way of doing it. Better would be a copy sop and stamping because with the switch you'd need to refer to a node higher up the network, not immediately before, or perhaps with opinput(), but it gets all rather messy later on I reckon.

However, I attached a file for you to inspect your case (press play to see switching) because I don't know what you would eventually like to do, so it may after all be the right solution for you!

switch.hipnc

Edited February 15, 2011 by Macha

[hopbin9]

Why use a switch? It's just extra work for Houdini. If you know the charge at the time of setting the color, then use an expression to create a different color. You don't even need to create an attribute if that's all it's doing is changing the color.

[jfrancis]

Why use a switch? It's just extra work for Houdini. If you know the charge at the time of setting the color, then use an expression to create a different color. You don't even need to create an attribute if that's all it's doing is changing the color.

Create a color where? In the color node? It doesn't seem to accept local variables, and I need that $CHARGE for something later.

[jfrancis]

Uhm...first of all I'd say use a detail attribute. But even then, the switch sop does not accept it directly as $ATT, you need a detail() expression. But even then this is not a very clean way of doing it. Better would be a copy sop and stamping because with the switch you'd need to refer to a node higher up the network, not immediately before, or perhaps with opinput(), but it gets all rather messy later on I reckon.

However, I attached a file for you to inspect your case (press play to see switching) because I don't know what you would eventually like to do, so it may after all be the right solution for you!

This seems to work for me (although I replace the %2 with a more complex noise-based function)- thanks

I didn't realize I needed this detail() function to access the data. I thought a $ANDSOMECAPITALLETTERS would be enough of a way to reference the detail attribute data.

[Macha]

Here's a few more ways to do it.

By the way, $ATT doesn't work always. If you look in the helpfile you'll see which node accepts wich local attributes. Often you can get it to work by using a point(), prim(), vertex() or detail() expression.

Also, vector attrib components are usually referred to as something like $ATTX $ATTY $ATTZ, whereas that is not true for 3 floats. Just something to be aware of. Color itself is a little unusual in that you refer to its components as $CR $CG and $CB, unless they are volumes in which case they are Cd.x Cd.y, Cd.z

Aaaahhh....

switch.hip

Edited February 16, 2011 by Macha

[jfrancis]

thank you