Geometry smoothing issues

[acrobaticpoly]

Hi everyone,

I'm having what appears to be smoothing issues with my geometry but I don't know how to solve it - not come across this before. Some sort of strange shading/artifacts when I smooth it - the rest of the model shows no problems but this little area seems to cause problems. I've attached an image for reference.

No flipped normals and vertices have been welded. I've tried quite a few smoothing methods to fix it but nothing seems to work.

I've also applied a default material to the model to ensure it didnt stem from the material.

I would really appreciate anyone who might know a solution!

Cheers

[romullus]

Sometimes Max does these strange smoothing weirdness for no apparent reason. Try to add edit poly modifier and collapse the stack, or convert object to editable mesh and then back to editable poly. Also you can go to polygon sub-object mode, select all and detach to new object. Lastly there's so called "box trick" - create box primitive, convert it to editable poly and attach your broken object to it, then delete box's polygons.

[maru]

I would also try:
- resetting xform
- checking if those are not UHD Cache artifacts - go to Render Setup > Performance and switch both the primary and the secondary GI solver at the top of the window to Path Tracing

[acrobaticpoly]

Thank you for the speedy responses guys, unfortunetly none of those worked. I've instead settled for pushing the turbosmooth iterations to 3, issue is still there but less obvious.

Thanks anyway guys, any other thoughts are welcome as I'll keep trying.

I might upload the file too if that might help?

[maru]

Yes, that would be great. If you can't / don't want to share it on the forum, please submit a ticket and attach your file here: https://support.chaos.com/hc/en-us/requests/new

[romullus]

Thank you for the speedy responses guys, unfortunetly none of those worked. I've instead settled for pushing the turbosmooth iterations to 3, issue is still there but less obvious.

Did you check for presence of not welded, or overlapping vertices?

[pokoy]

The problem is the slight shadowing or the black edges on the smaller geometry?
If your problem is that adding a Turbosmooth mod produces those black edges, what happens if you check on/off 'explicit normals' in the modifier? Is it looking better when using a Meshsmooth modifier instead of Turbosmooth?

[acrobaticpoly]

Thank you for the speedy responses guys, unfortunetly none of those worked. I've instead settled for pushing the turbosmooth iterations to 3, issue is still there but less obvious.

Did you check for presence of not welded, or overlapping vertices?

Yep I've tried this already but things seem to be all good.

I've attached the file for anyone who wants to try to have a go.

Many thanks in advance guys!

[acrobaticpoly]

The problem is the slight shadowing or the black edges on the smaller geometry?
If your problem is that adding a Turbosmooth mod produces those black edges, what happens if you check on/off 'explicit normals' in the modifier? Is it looking better when using a Meshsmooth modifier instead of Turbosmooth?

Its the strange shadow looking lines on the edge of some detail. Looks slightly better with mesh smooth I guess but not much more to warrant good enough.

I've tried turning on/off explicit normals too but to no avail. I've attached the file above, feel free to have a go at it. 

Cheers

[romullus]

Oddly enough, the issue turns to be in the terminator handling that Corona uses to combat shadow terminator issue. If you turn terminator handling off, this will fix your shading issue completely. You can find terminator settings in render settings, dev/debug rollout. Mind you, that if you chose to turn this setting off, you will need to watch your scene for unwanted shadow terminator artifacts.

Alternatively, you can improve your mesh topology by adding more geometry where the artifacts shows. I did this with the chamfer modifier and got significantly improved results with only marginal increase in polycount. Attaching some pictures for comparison and the scene with the fix. Notice that fixed mesh looks arguably better than original with 3 iterations of turbosmooth, which adds over 5 million triangles to the scene. Bear in mind that the lighting is deliberately set up to show artifacts as bad as possible. With more normal lighting setup, the issue should be almost completely invisible.

[Aram Avetisyan]

Check the edge orientation in the set model. Sometimes it can be crucial for correct smoothing results.
I would recommend recreating the problematic parts, if possible.
You can simply delete the loop of polygons and shift-drag-create new geometry, it should be smoothed fine.

[pokoy]

I'd like to have a look at the geometry but it seems it's saved in Max 2023 - could anyone save it out as a Max 2021 file?

[romullus]

You can download the file attached to my previous message, i think i saved the scene to Max2020 format and it has original object in it.

[pokoy]

That's a funny mesh.

While it's true that the shadow terminator fix in Corona is producing the shading errors and shading is good if it's disabled, the mesh sometimes shows a problem I've seen a few times - for some reason, hard edges appear out of nowhere and are persistent even if the mesh is smoothed or Turbosmooth is used, but unlike with this mesh it's always already visible in the viewport. In one recent case I was able to get rid of the issues by using OpenSubD instead of Turbosmooth. But that's not related to Corona, it's a Max problem.

I tried everything I usually do to get rid of these but in this case nothing helped, and it's strange you have to disable the shadow terminator fix to get it to render correctly. Usually this needs to be done with meshes with explicit normals which this mesh doesn't have.

I guess it's something for support to have a look at since this doesn't make any sense.

One question - does the mesh come from the Retopo modifer? And if yes, was the source mesh a CAD mesh and it was processed with 'Specified Normals' enabled within the Retopo modifier?

[acrobaticpoly]

Oddly enough, the issue turns to be in the terminator handling that Corona uses to combat shadow terminator issue. If you turn terminator handling off, this will fix your shading issue completely. You can find terminator settings in render settings, dev/debug rollout. Mind you, that if you chose to turn this setting off, you will need to watch your scene for unwanted shadow terminator artifacts.

Alternatively, you can improve your mesh topology by adding more geometry where the artifacts shows. I did this with the chamfer modifier and got significantly improved results with only marginal increase in polycount. Attaching some pictures for comparison and the scene with the fix. Notice that fixed mesh looks arguably better than original with 3 iterations of turbosmooth, which adds over 5 million triangles to the scene. Bear in mind that the lighting is deliberately set up to show artifacts as bad as possible. With more normal lighting setup, the issue should be almost completely invisible.

Very useful information! Never come across this "Terminator Handling" before, very interesting to know.
Yes, adding a chamfer to the edge certainly helps.

Thank you very much to everyone who offered thier solution; I learnt a fair bit :)