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Any suggestion in creation of leaks(dirt) from horizontal planes (black color planes on picture)? enter image description here

Thank you. I tried myself to do some sort of mask for leaks or dirt ...but not very accurateenter image description here

Reference picture of wall with leaks enter image description here Some updates how to separate horizontal black lanes

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    $\begingroup$ Hi, thanks for the question. Can you include some reference photos of the effect you're trying to create, and expand on your description? $\endgroup$ Commented Dec 5, 2020 at 23:11
  • $\begingroup$ Welcome to the site! As Allen mentioned, it would be good to get some more information about what you're after. Just looking at your image, it could be a number of things. Have you checked the normals to make sure none are flipped? $\endgroup$
    – fmotion1
    Commented Dec 6, 2020 at 1:47
  • $\begingroup$ maybe share a part of your file: blend-exchange.giantcowfilms.com $\endgroup$
    – moonboots
    Commented Dec 6, 2020 at 8:50
  • $\begingroup$ I added some details for question. Thank you! $\endgroup$
    – stakatch
    Commented Dec 6, 2020 at 12:35
  • $\begingroup$ Could you be more specific about what you want to do? The desired effect is completly subjective. $\endgroup$
    – lemon
    Commented Dec 6, 2020 at 12:59

1 Answer 1

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I think that I have methods for both simple and complex shapes. To set up our scene I have this model that I've assigned this PBR texture.

enter image description here

For now we want to treat this as a simple shape and generate a leakage map on the top edges.

To do this we need to be looking at Generated Coordinates separated into only the Z axis.

enter image description here

Now, separately, we can generate some noise and scale it on the X and Y axes with a Mapping node and we get the beginnings of some sort of overall leakage map.

enter image description here

If we mix this noise into our coordinate space and look at the Z coordinate now, we have generated a leakage gradient.

enter image description here

Now we can use a Math node set to Subtract to control where this gradient terminates.

enter image description here

Once you have it placed, I would use a Multiply operation (also clamped) to bring the values up.

enter image description here

Now we can go back to our original PBR setup. What I did to apply this is simply drop a Hue/Saturation node on the base color and use this black and white map as the factor input.

enter image description here

You have all of these sliders to adjust the effect.

enter image description here

And if you need more variation, feel free to mix in as many layers of noise as you want. You'll be constantly adjusting your termination zone, though.

enter image description here

So this should work for pretty much any simple shape, but you'll notice there's a lot missing from this. For more complex shapes you could always generate several masks and add them together, but if we want it to automatically account somewhat for corners and especially windows we need to look to the Bevel node.

If we set our bevel radius pretty high and separate out the blue channel, we basically catch every top face and a bunch of the connecting faces.

enter image description here

We can use similar methods to mix this into our noise layers and come up with something like this.

enter image description here

Which I think works pretty well. I'm not exactly 100% happy here, but considering you can just mask out anything you don't want and can mix and match methods I think I'm satisfied to finally leave the answer here.

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  • $\begingroup$ I love the bevel trick, it is very convenient :) $\endgroup$
    – Gorgious
    Commented Jan 28, 2021 at 20:26

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