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I used this fresnel setup on top of my shader to create a artificial rim light effect enter image description here enter image description here

But of course fresnel is applied around the entire object, is there a way to control the sides of the object it is applied so I can emulate a rim light effect comming only from the left?

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  • $\begingroup$ I'm testing things tryng to find a solution, but no luck so far. I have an idea (maybe), however I need to know if either the light direction or the camera angle are going to change (example: you want only the "left side" to have a fresnel, does "left" mean the left side of a still image. or does it mean the side that's always farthest from the camera, or does it mean the lit/unlit side)? $\endgroup$
    – Christopher Bennett
    Commented Jul 10, 2020 at 6:40
  • $\begingroup$ Ideally it would always be the unlit side, but having a parameter where I can change the direction of the fresnel at will would work as well. $\endgroup$
    – Bruno Marquez
    Commented Jul 10, 2020 at 22:06

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I think you want to mess with the Geometry Node. This is me just plugging in the first random value that comes to mind, but I'm sure playing with some of the other attributes might work even better. enter image description here

Result:

enter image description here

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You can do this, in a number of different ways, without any matcap or anything:

enter image description here

Left to right: original; rotated normal; directionally limited Fresnel.

The Fresnel calculation looks at the relationship between incoming ray and the surface normal to get its output. We can send the Fresnel node a false normal ouput, which we have altered in some method, to get Fresnel as if the normal were something else:

enter image description here

We could also just check which direction the normal is facing, and make out emission black if it's facing the wrong direction:

enter image description here

Here, I'm comparing the surface normal to the object space -1,0,0 vector. If the surface normal is facing that direction, we'll do the full emission. If it's parallel or facing away, we'll do black instead. Between, we'll interpolate.

There are plenty more imaginable methods, and any of these can be adjusted however desired. A single map range node can go a long way....

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For those interested, I have achieved what I wanted with a matcap setup, the problem is that its not easily editable and I have to put a new image file every time I want to make adjustments, I'm still open to now if theres a way to do it with a fresnel node

[enter image description here enter image description here

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