I recently saw this post and thought the matcap looked absolutely amazing, but unfortunately I wasn’t able to locate the original (according to the person who once “originally” posted it online, he suspected it was something he lifted from a proprietary software package anyway).
Since @Rhino_Bulgaria already showed me how to set them up in Rhino, I set out to recreate one for my own personal use (with slight changes):
Now, I made this 1k x 1k large, while most matcaps I’ve seen online has been 256px or 512px. Is this too large for Rhino? Or can I even do 2k? I ask because if you look at the image above, I feel like I can actually even use it to find curvature continuity issues, but the sharp lightbox gets pixellated on large, flat surfaces. Does @nathanletwory or someone have any insight or recommendations here?
I made the matcap available for download here and yes, maybe it’s a bit extreme “candy coat” and I’ll get tired of it real fast, I don’t know… I made a blue 2k version for testing with here as well.
Matcaps are intended for showing form on curved surfaces. I know them from Blender sculpting. Flat surfaces don’t lend themselves well for matcap usage.
I suppose the projection of the spherical map onto a flat surface shows as blocky as there is no gradient between the normals of the different locations on the flat surface, so you get into very small area being sampled in the matcap texture.
These do look nice - if you want to use them with Rhino Physically Based material you can: put the texture in the base color slot, then set its projection to Environment Map > Spherical
While the environment maps help to spot some inconsistent continuity between surfaces, it could also lead to false impression for a lack of continuity where it’s actually perfectly fine. That’s because the environment maps rely on adding gradient and fake reflections on the 3d geometry via consisting shiny “reflections” that are draw on the image for that very reason. It’s especially evident on flat surfaces where the environment map is being “reflected” in such way that the surface no longer looks flat despite being perfectly flat.
Here are two examples that show how the environment map appears with sharp edges that suddenly change their orientation, whereas the geometry itself if smooth and with G2 continuity between the surface patches:
When you use PBR as the material to put your matcap in, make sure that everything else is essentially turned down - the matcap is supposed to give the ‘reflection’ and material properties. Set specularity, sheen, clearcoat to 0.0 manually.
If you want you can play with the alpha value (don’t use opacity, that will mess with the effect instead of do what you rightfully might assume). Below the reds are from back to front with alpha 0.75, 0.50, 0.20. The blue obviously has alpha 1.0.
I’ve been interested in a matcap display for a while in Rhino, but just recently set it up. If you want to have matcap material as a default for the view, you can set up a custom Display Mode and use a custom material as the environement. Hope this helps!
It’s especially evident on flat surfaces where the environment map is being “reflected” in such way that the surface no longer looks flat despite being perfectly flat. 
