To come back to an earlier topic I posted here.
I try to make my question more simple.

I followed this tutorial: https://www.youtube.com/watch?v=WySzeEniScs&ab_channel=timjdesign [www.youtube.com]

The purpose is to fill an imported obj with particles in the same way described in the tutorial, but from left 100% particles, to the right where you have 0% particles, with a smooth transition. I've made some quick sketches in illustrator to give an idea.

And is there an other way to use instead of the pop color node with the alpha? Because I've tried many times to import an alembic in c4d octane with the Cd attibute but no result showing up in the render.

who can help me out or show me a tutorial where I can solve this problem?

best,

Since you mentioned that it's for a still image you really don't need to simulate it. You just use a Scatter node to put particles on your imported geometry. Afterwards, doing the left-to-right fade can be done for example in a point wrangle (the example assumes that your font is along the X axis):
vector bb = relbbox(0, v@P);
f@Alpha = bb.x;

I can't help with the Octane shader, although I'd imagine that there is an Octane node that allows you to bring an attribute into your shader, then connect it to something like opacity or transparency. Maybe someone else here knows precisely.

Digipiction
Since you mentioned that it's for a still image you really don't need to simulate it. You just use a Scatter node to put particles on your imported geometry. Afterwards, doing the left-to-right fade can be done for example in a point wrangle (the example assumes that your font is along the X axis):
vector bb = relbbox(0, v@P);
f@Alpha = bb.x;

I can't help with the Octane shader, although I'd imagine that there is an Octane node that allows you to bring an attribute into your shader, then connect it to something like opacity or transparency. Maybe someone else here knows precisely.

Thanks Digipiction,

I found this tutorial for exporting alembic to c4d, but no tutorials how to handle alembics with alpha ... https://www.youtube.com/watch?v=g2iz8PDn32E&ab_channel=%E5%88%98%E6%B4%AA%E5%AE%87 [www.youtube.com]
But does it have to be with alpha? Is there not any other way to have the particles in Houdini, going from right (100% particles) to left (0% particles)? Maybe in the scatter node with some specific settings?

I don't think Alembics handle alpha, this concept doesn't really exist for 3d models. The "Alpha" attribute in Houdini is just a special attribute that gives you a rough viewport preview of the opacity, just like the "Cd" attribute gives you a preview of the color. But even in Houdini when rendering with the various engines you need to actually connect it up for it to have an effect in the rendered image.

You can completely follow the tutorial you posted if you store the information in a Cd attribute instead of Alpha. In the wrangle I posted above, change the second line to:
v@Cd = bb.x;

Then in the tutorial video where he hooks the Gradient node up to the Diffuse port, you would hook it up to the Opacity port instead.

timwtw
Is there not any other way to have the particles in Houdini, going from right (100% particles) to left (0% particles)? Maybe in the scatter node with some specific settings?

Yes sure, you can use a density attribute, there's a checkbox for it on the Scatter. The look will be different of course, because the particles get more and more sparse instead of less and less visible.

Many ways to create the density attribute, to stay with my previous example, you would use the point wrangle on your font before plugging into the scatter:
vector bb = relbbox(0, v@P);
f@density = 1 - bb.x;

Here is a non-VEX way: