7 answers · asked · Lesson: Sharpening the Details · Course: Introduction to Retopology

Subdivision modifier curving edge (2.80)

The edge in the center of the image is getting curved by the subsurf modifier, causing all kinds of chaos. Left alone, it causes a weird shading artifact. But when adding a loop cut as a holding edge, it tosses the new vertex out along that curve (in the same plane), causing the geometry to hang over the corner:

No amount of jiggling the vertices or recalculating normals seems to fix it. Setting the edge's Crease strength to 1 keeps it straight but causes more shading artifacts at the two vertices. As far as I can see, my geometry in that area is identical to yours.

Is there some way to fix that edge?

  • crew

    To fix this you'll need to either a) sharpen the top-most edge that's overlapping or b) add holding edges along the corner that go up and over. 

    Sharpening this edge is probably the simplest method, although it may not give the sharpest results:

    • By "sharpening the edge", do you mean increasing its crease strength?

      Doing so causes this shading artifact (A small divot in the surface at both vertices), as stated in the original question:

      Adding holding edges along the aberrant edge causes a sort of stretching at that far vertex:

      Sorry if it's hard to see in the pictures. The artifacts are much more apparent when tumbling around in the 3D viewport.

  • Hi siegen! 

    Just a wild guess; do you have a double vertex in that corner?

    Select the corner vertex and move it, see if a vertex is left behind. Escape to cancel the transform. In case there was a double vertex:

    Select all, ALT M > Merge by Distance....

    • I wondered that myself but I can't find any extra vertices. I tried merging by distance and moving things about.

    • Then maybe it's the other classic: flipped normals???

    • That's an interesting screenshot but doesn't seem to be the problem here, I think. I tried recalculating normals in the OP and tried manually flipping and resetting the normals for the few vertices around the problem corner once I saw your screenshot. But none of it seems to affect that edge in a good way.

      Best I could get was straightening it out by flipping one whole face along that edge but that's not really preferable:

  • ssiegen could you send a link to your .blend? (Dropbox or Google drive or whatever cloud service...)

    I'd be happy to take a look. Can't guess what is causing this from the screenshots.