Geometry nodes, how to emit particles only at the edges of the mesh

Support Particles and Physics Simulations
1

Hello, I am troubled by the issue of not knowing how to emit particles on only certain parts of the mesh/object.

You can see on this screenshot how I managed to make the red color be only at the certain parts of the object, I did that in shader editor with the help of “Geometry → pointiness”. I am okay with that but I don’t know how to emit particles (lets say cubes to be used as crystals) from those certain red colored spots on the monkey head.

I would be grateful if somebody could explain me if that is possible in geometry nodes or in particle system.

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2

I believe you could use a similar resource, a vertex dirt paint in vertex paint mode to create an attribute you could use for that. I don’t think you can use shader nodes. But I can be wrong.

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3

Thanks for the reply but I dont want to hand paint anything, I can do that with vertex paint or weight paint (without even using geometry nodes).

4

You don’t need to hand paint anything. Dirt paint (dirty vertex colors) is an automated resource in the vertex paint mode.

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5

It gives you this result that is converted to vertex colors which is an attribute you can use.

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You get it here:
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6

Ohh thanks a lot, can you please show me a geometry node’s node setup if I want to emit cubes from those black/darker areas?

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I’m not an expert in geonodes. It may take a bit to do it. :joy::joy::joy::joy: I will try, anyway.

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8

I did this very rudimentary one. I needed to tweak the dirty vertex paint and did not rotate the instances or anything.

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You can use the minimum and the maximum values of the map range node to control the distribution a bit. You could use a math node as well. There are many ways, in fact.

I used the map range to control the intensity and to invert the dirty paint because black is 0 and not 1.

Here with the minimum to 800 and maximum to -3000:

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And these are the dirty vertex parameters I used for this one:
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9

One more test with some light chrystals I had here just to see what it looks like:

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I hope that matches your needs.

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10

Thanks for the help but the cubes are not being shown on the vertex color map.
They are emitted randomly

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11

dirty_geonodes.blend (521.3 KB)
Here, take my blend file. You can study what I did there.

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You can use boolean as a switch too.

Beaten by @Calandro

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13

There are so many ways to do something in Blender. That’s wonderful and frightening, I know, but wonderful. :joy::joy::joy:

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14

Better to keep my enthusiasm low. I don’t want to be flagged again in one day. Ops. Probably I will, now. :face_with_hand_over_mouth::joy::joy::joy::joy:

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15

I copy pasted the geometry nodes from your file into mine, I set up vertex colors on my own 3D model and I applied those geometry nodes you used on your 3D model.

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The main issue is that my vertex colors on my 3D model are not even recognized in geometry nodes.
I am using blender 3.2.1. , your blend.file works with applied settings but my blend.file doesnt work with those same applied settings. I did tweak plenty of things in those same geo nodes but nothing works, its like those vertex colors are not even recognized on my 3D model.

here is the link to my file: https://we.tl/t-MVT6aQbR8l

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16

Ok, I will give it a look and tell you something in a few minutes.

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You need to select yr vertex group Col here.

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18

Oohhh dang, thank you a lot. I knew it that I missed something hahaha.

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19

Yes, As @AlphaChannel said, you need to select your vertex color attribute to make it work. Also, you removed the values in the map range that inverted the selection. This way you will have crystals only where you don’t want to have them.

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20

Thanks a lot for that too. I knew it when you sent me your file, if that doesnt work then probably we missed some little detail that will be a determining factor about if things will work or not.

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