Scaling the size of copy stamp boxes using an effector or something else?

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Hello, I'm trying to replicate the bridge forming effect from this video:
https://youtu.be/lx2dLrXyyIA?t=3m58s [youtu.be]
From 3:58 - 4:00

I've already created the look of my bridge by copy-stamp the boxes to the scattered points.
However, I tried using the method from tokeru:
http://www.tokeru.com/cgwiki/index.php?title=Houdini#Instance_with_effector. [tokeru.com]

But unable to achieve what I seek. What is some work about on achieving the effect?

Any help will be appreciated, thanks.

Attachments:
Test_Bridge.bgeo (357.5 KB)
Test_V01.hipnc (593.5 KB)

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One way is to create a group using an animated bounding box. Instead of using the old school $PT to create the random scale use an AttributeWrangle instead. In the wrangle, initially set the random scale as you are currently doing. Then examine if the point is currently in the group. If so scale the random number down or up by some amount. As the bounding box moves along the points the scale will change the points within the bounding area.

The updated nodes are in purple. You have to remove the old RandomScale variable and instead use the Attribute Stamps field to “relay” the attribute version of RandomScale into the Copy to make it available for stamping.
Edited by Enivob - 2017年2月6日 09:21:46

Attachments:
Untitled-1.jpg (151.4 KB)
ap_Test_V01.hipnc (605.4 KB)

Using Houdini Indie 20.0
Windows 11 64GB Ryzen 16 core.
nVidia 3050RTX 8BG RAM.
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Thank you Enivob for your set up.

But I have a question, how do I get the other points to remain scale 0 when it's not selected by the group, while only those grouped by the bounding box will scale back to the randomly set scale size?

Because currently, it looks like I'm simply deleting it. Sorry for the trouble.
Edited by YH - 2017年2月7日 01:14:45

Attachments:
ap_Test_V02.hipnc (607.1 KB)

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I'm not sure exactly what you mean but you can invert the logic in the attributewrangle code.
// Start off with all points getting a random scale.
f@RandScale = fit01(rand(@ptnum),0.050,0.1);
if (@group_effector != 1) {
    // If the point is in the group scale it down a bit.
    //f@RandScale *=0.01;
    // Or just set the scale to zero.
    f@RandScale = 0;
}
Using Houdini Indie 20.0
Windows 11 64GB Ryzen 16 core.
nVidia 3050RTX 8BG RAM.
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Thanks for the tips.
Just a student learning Houdini
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