Shading issue...

Ladytron · Jun 2021

Hi.
I'm having an issue with smooth shading. I'm using Blender 2.76.

Image: https://us.v-cdn.net/5021068/uploads/editor/06/7w8kxfmav81u.png

Image: https://us.v-cdn.net/5021068/uploads/editor/ij/5axjs3nx09mm.png

As you can see from the photo, the shading isn't smooth. There are lines showing. I've tried to bevel the edges but that didn't fix the shading. I did use Knife Project on the sides and that seems to be when the shading messes up. Also, I'm using Auto Smooth.

Here is how it looks before/after using Knife Project.

Image: https://us.v-cdn.net/5021068/uploads/editor/rj/15g9q5l9vry3.png

If anyone know how to fix this, I'd appreciate the help.

Thank you!

Kanni3d · Jun 2021

Show us your wireframes? Likely has to do with the two intersecting cylinders segments not lining up. If even if they are an even amount perfectly and are welded/lined up, the curvature of the cylinder could ruined the moment you move/weld things out of place, giving you those shading artifacts.

gnoop · Jun 2021

There is two approaches for such issues.

a) Making edges meat each other in intersection line Plus extra edge loops right/left of intersection line .

b) By working with vertex normals only with whatever actual tessellation where you can use data transfer modifier to project /borrow/ suck in normals from each of two initial cylinders ( subdivided for perfectly cylindrical shape) to respective parts of your model . Intersection line should be split so edge vertexes wouldn't have shared normal . You can merge vertexes later but still have to mark intersection edge loop split ( cyan colored)

If you want to use subdivision with this second method you need to check in "custom normals" in subdivision modifier and be carefull with extra editing since any new loop could modify transferred normals and you would have to do it again.

Ladytron · Jun 2021

Thank you guys for the replies @Kanni3d and @gnoop !

So I think I understand what you guys are saying to do, maybe I'm wrong. I used the knife tool to make edges...

Image: https://us.v-cdn.net/5021068/uploads/editor/st/f8s3fom5027e.png

... but it didn't fix the issue. You can still see lines.

Image: https://us.v-cdn.net/5021068/uploads/editor/xh/vjyxx97x54hs.png

I'm not really comprehending the second method you mentioned @gnoop.

Kanni3d · Jun 2021

Yeah, judging from the wireframe:

too many edges
edges/cylinder segments on the inare not evenly spaced, ruining the curvature already
edges are not lining up with the perpendicular cylinder edges

Depending what this mesh is used for (offline rendering? game art? highpoly/sub-d model to be baked down?), just start with a really low amount of segments. This will ensure it's much easier to manage merging the two together, and easier to control the shading.

In essence, this issue you have is just due to way too many erratic segments, which are then smashed together.

Preparing the two meshes to be welded/booleaned/merged together, ensuring the segments are low and manageable, and line up

Image: https://us.v-cdn.net/5021068/uploads/editor/xs/zydth4eeawed.png

Booleaned together, no stray vertices, edges are straight and preserve the cylinders curvature

Image: https://us.v-cdn.net/5021068/uploads/editor/eb/l7z4j6sw27iz.png

Added additional holding edges/support loops for sub-division.

Image: https://us.v-cdn.net/5021068/uploads/editor/sr/otllzk2489r9.png

gnoop · Jun 2021

I'm not really comprehending the second method you mentioned @gnoop.

Shading of polygons in 3d graphic is being defined by vertex normals . Its inclination to surface . https://en.wikipedia.org/wiki/Vertex_normal

Typically Blender calculate/set vertex normals automatically by polygon/edge flow . Thus you do those support loops and regular tessellation to help 3d package set vertex normals right in automatic manner.

3d package is stupid like rock really and have no AI to figure out on its own that a cylinder shouldn't have any shading odds ( why still not in 2021 I am not sure) so you do those "right" tessellation and redundant edge lopps with only purpose to help the soft to do it right.

The second method is not helping 3d package to set it right through edge/polygon flow but rather by setting those vertex normals directly/ explicitly whatever crazy underlying polygon flow or edge loops might be . Such vertex normals are called "custom normals" in Blender and "explisit" normals in 3d max .

If you couldn't allow all the extra geometry/ edge loops to make it right automatically ( in mobile games for example) it's sometimes simpler and quicker to just rotate those normals to their right positions manually or "borrow"/ transfer / project them from another piece of geometry where the shading is perfect already. Data transfer modifier in Blender , attribute transfer in Maya , or normal theft script for 3d max do that.

sacboi · Jun 2021

@Ladytron

Curious, if there's a specific reason for generating longitudinal manual cuts on a curved surface using the knife tool, combined with auto smoothing the mesh?

Shading issue...

Replies