Michael Mirn (michaelmirn)

4 answers · asked on Glossy Reflection

About Glossy/Fresnel

Do I understand correctly that if you use Fresnel you no longer need to mix Glossy with anything? So basically you'd use that shader as an additional tweaker for Fresnel?

  • michaelmirn Hi Michael, I don't think you understand it correctly, but then again it is not really easy.

    The Fresnel Node in CG is trying to simulate an effect, that is often called the Fresnel effect.

    For ease of understanding, let's imagine, that you are standing at the edge of a lake. Now, look down. You can see through the water. There will also be a faint reflection of your face. If you look at the opposite side of the lake, the water will appear highly reflective. This is what the Fresnel Node is trying to simulate; The Glossy Node represents the reflection (when the Roughness of the Glossy Node is set to 0, the reflection is 'mirror-like'.). If you would simulate the lake, you would mix a Glass Node with a Glossy Node and use the Fresnel Node to decide the Factor of the Mix Node.

    theluthier used the Fresnel Node as a Factor to mix between a Diffuse and Glossy, to make a paint material.

    The Fresnel Node is meant to be used as a Factor of a Mix Node, usually the bottom one being a Glossy Node.

    Nowadays we have the Principled BSDF, which has the Fresnel 'build in'.

    It's actually quite complicated and I hope I didn't confuse you more than helping;)

    • Yes, it's still a bit vague for me and I guess the only way to deal with that - to practice more and more.

      I know about Eevee, yes, but I believe that's good to dwell in the previous versions, helps me to understand the principles. I really love how flexible and powerful Blender is.

      Thanks a lot for your explanation!

    • crew

      Another exquisite explanation from spikeyxxx, thank you!

      The only thing I will add is that the fresnel inclusion in the Principled BSDF was recently called into question with this video. Essentially it seems that the Principled shader uses fresnel automatically in relation to reflection amount but not in relation to reflection roughness. Kinda odd..I hope the devs change that since fresnel definitely should effect both.

    • theluthier nice video, but unfortunately incorrect. He claims that towards a 90° viewing angle, every material has a perfectly mirror-like reflection (all of his curves end at 0). A rough material however, will never have a roughness of 0! No matter at which angle you look at it. I checked all of my matte-painted walls;)

      There is also the issue, that in CG the Fresnel is calculated from the viewing angle, while in reality, the Fresnel is calculated from the light direction....But all of this is extremely complicated and I would suggest to not worry about this and just make amazing looking art! If it looks good, it is good;)