Hello everyone! Is it possible to keep an attribute with the last written value even when it is not being rewritten?

I have observed that when the attribute wrangle does not save that function for example due to a conditional, the attribute disappears.
I have a scene in which I need to save the position information over time to resume it later incrementally.

My intention is to increment an attribute intermittently, so that it grows without going back to zero when it is not being written.

I attach the scene with the example given in the detail attribute.

Hi,

For these situations, you have to use the Solver SOP to preserve history over time.

animatrix_
preserve history over time

I am honored by your response Yunus. I cannot get the attribute "pos" to grow procedurally at the pace of a caterpillar. Always forward but with pauses. I am trying to do it with Solver SOP. I sense that this is a key point to understand Houdini's logic. In any other environment you simply store the information in a variable. Here it seems to start from scratch every frame.

You tried it like this?



If it's still not doing what you want, you might want to change the logic inside to have intermittent pauses.

Thank you very much Yunus for insisting on something so simple for you. The idea is to take the values ​​of a sin() function but only when it is growing between 0 and 1, with the objective of obtaining a variable "pos" that grows indefinitely in an intermittent manner, guided by the determined rhythm of the sin function. I would like to do it without depending on keyframes to understand this particular Houdini logic.

Hello,

Using the Solver SOP is of course the way to do what you are looking for, but the Attribute Wrangle inside is missing something to make it work as intended.

If you want to keep the previously written value, then you have to store it in a variable and return it when the "if" statement condition is not satisfied.



Not sure why you need velocity from another geometry, you can find an example with velocity as well in the hip file.

ObeidaZakzak
Hello,

Using the Solver SOP is of course the way to do what you are looking for, but the Attribute Wrangle inside is missing something to make it work as intended.

If you want to keep the previously written value, then you have to store it in a variable and return it when the "if" statement condition is not satisfied.

// get current pos attrib value
float pos = detail(0, "pos");

// initialize offset value to add to pos attrib
// when "if" statement is not satisfied then offset is 0 and will not affect pos attrib value
float offset = 0;

// sin function values are always between -1 and 1
// enter "if" statement only when sin value is between 0 and 1
float signal = sin(@Time * chf('speed'));
if (signal >= 0) {
    offset = chf('units') * signal;
}

setdetailattrib(0, "pos", pos + offset, "set");

Not sure why you need velocity from another geometry, you can find an example with velocity as well in the hip file.

This is exactly what I needed to understand Houdini's logic regarding the memory of variables!
Believe it or not, this opens up a world of possibilities for implementing ideas.
I believe you are a social benefactor operating within the jurisdiction of the galaxy.
Thank you very much for your help Obeida.