Point cooler from scatter using attribute wrangle

[defc0n1]

Hey guys.

I'm pretty new to the houdini world, and I've been experimenting a lot of things. Is there a way to get the RGB values of scattered points using attrib wrangle? Im not too familiar with the VEX syntax, so Im having a hard time figuring it out. I have random colours signed to a scatter node and some geometry copied on to the points using a copy node. I want to limit  scatter the geometry based on the colour of the scattered point. Thanks!

[Atom]

Sure, with a wrangle running over points, you have access to each points color with the @Cd attribute. In this code, any objects that have a red color greater than 0.9 will be scaled to 0, thus not appear in the scene. All others will get a scale of 1 and appear in the scene.

if (v@Cd.r > 0.9) {
    v@scale = 0;
} else {
    v@scale = 1;
}

 

Edited January 3, 2017 by Atom

[Skybar]

5 minutes ago, Atom said:

Sure, with a wrangle running over points, you have access to each points color with the @Cd attribute. In this code, any objects that have a red color greater than 0.9 will be scaled to 0, thus not appear in the scene. All others will get a scale of 1 and appear in the scene.

if (v@Cd.r > 0.9) {
    v@scale = 0;
} else {
    v@scale = 1;
}

 

Just a heads up that this can be problematic, even though they're not visible they are still there. So potentially you could end up with tons of infinitely small geometry; they aren't visible but still take up memory and whatnot. 

[Atom]

Skybar is right, just keeping it simple. This is an old mograph trick and is safe to use up to hundreds of objects/points on most hardware. If you get up into higher points counts you may want to remove the points that you don't want copies on.

Like so.

if (v@Cd.r > 0.9) {
    removepoint(0,@ptnum);
}

The @ptnum attribute is the actual point number that the wrangle is currently evaluating. If you are running over primitives there is a similar attribute called @primnum.

Edited January 3, 2017 by Atom

[defc0n1]

Thank a ton, guys! You're awesome. Works like a charm. The sheer power of Houdini has me in awe, actually. 

Can I export a variable or set a parameter based on the input Cd that I can access from other nodes? For example a switch?