# Make Part of Material Light Up with Plain Effector

#1

I was wondering if it’s possible to make part of an object light up using a plain effector. For example, suppose I have a really long rectangular prism in my scene and I want the luminance channel to become yellow if a plain effector with a box falloff passes through the object and black otherwise. However, when object lights up, the whole thing shouldn’t become yellow; only the part within the box falloff of the effector.

Here’s a video showing the problem: https://www.youtube.com/watch?v=jwCXkUYPDbk&feature=youtu.be

I can’t figure out how to do this without making the whole thing light up. Any ideas?

#2

Gotta be something you can do using Fields to control the area of the effect…

#3

I’m not sure since it’s a property of the material itself. If it is possible the way you suggested, can you give an example of how to set it up?

#4

Make geometry editable (note : you will have to subdivide your geometry first as much as required for the detail you need), select a vertex point and choose Select>Set Vertex Weight…now select the Vertex Weight tag and in Basic tab tick Use Fields. Now under the Fields tab, add any Field you want to achieve the effect you want.

Make 2 materials, one with Color and Alpha ticked and another as the color outside the Field Effector you’ve chosen.

In the material with Alpha selected, click Texture and choose Effects>Vertex Map. Now click on the Vertex Map and drag the Vertex Map tag into the Name slot. Make the color slot any color/material you want for where the alpha/Field Effector is.

Drag the materials to the geometry so that the outside color is to the left of the material with color and alpha.

Now, wherever the Field Effector is will be green and outside that will be white (in this example).

#5

Uh, yeah, that’s what I was going to say…

#6

Thanks, this was very helpful; but what would be the equivalent way in R19 or lower (since there aren’t fields)?

#7

You can get something very similar with a simple 3D circular gradient.

In xpresso, link the world coordinates of the center of the gradient to a null and set the radius to be your falloff and that’s it.

Best
Eric