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I’m animating a plate of steel cut by laser rays. My animation is complete for the most part of it but I want to make the overheating of the steel where the laser passes visible. As it passes it assigns another material with emission on the cut border of the meshes of the plate and the borders of the cut pieces.

The appearance of the material has to be animated according to the movement of the laser or even in key frames.

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You can achieve this effect by using the dynamic paint system. Select your steel plate and give it a dynamic paint physics modifier, set it to be a canvas. Then set your laser object to be a dynamic paint brush. Add a wetmap output at the bottom of the canvas settings.

Now in your shader settings you can get a vertex info node and set import the wetmap data. Plug this into a principled BSDF in the emission strength settings and make sure to add a blackbody node into emission colour for the correct colour. Then just mess around with the spreading dissolving and shrinking paint effects until you get the look you want.

enter image description here

You can download an example of the effect I think you are going for with this blend exchange link.

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  • $\begingroup$ Thanks a lot! this way works on a new file but I can't understand why it doesn't work on my file :-X can you please take a look at it ? drive.google.com/file/d/16y4fyNbm0k_ktgCiJrZdYcGSTUasfkjG/… $\endgroup$
    – Francesco Ferretti
    Feb 17, 2021 at 16:10
  • $\begingroup$ the laser rays are not perpendicular so I set as brushes invisible cylinders parented with the origins of sparkles which are the genitors of the lasers $\endgroup$
    – Francesco Ferretti
    Feb 17, 2021 at 16:14
  • $\begingroup$ You seem to have forgotten to actually connect the principled bsdf with the emission input into your shader. I'll try and fix it. $\endgroup$
    – Nascent Space
    Feb 17, 2021 at 22:49
  • $\begingroup$ No that’s there just for test if the mistake depend on the material but is not that, I think is on the meshes normal or maybe I need to subdivide it more but if I subdivide the big mesh blender create faces with non-parallels normals and it looks orribile $\endgroup$
    – Francesco Ferretti
    Feb 18, 2021 at 1:02
  • $\begingroup$ Ok I think I know what your problem is, your actual geometry is not suited to use vertex colour sourcing. You need to either add more geometry inside of the letters and outside of them or set it to UV and see if that works. Also you don't need the brush objects to be cylinders, just simple cubes works too. $\endgroup$
    – Nascent Space
    Feb 18, 2021 at 1:11

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