Terminator issue?

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MarsThunder
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Terminator issue?

Post by MarsThunder » Wed Oct 23, 2019 4:00 am

I just recently upgraded to 2.2 and I noticed something I did not see previously (or I was not paying attention at 2.1). A strange terminator-like issue with a non-sphere object. At first I thought it was a bump issue - separated bump. Then an image issue - separated image. Turns out it does this weird shadow thing (really dark like terminator thing of past) even with matt material. Angle change in relation to horizon does not make difference as depicted in next to last image.... Light angle pretty high too. PS: normals are good and pointing out like they should.

If a blend file is needed to test...let me know!
Attachments
High angle no problem
High angle no problem
Low angle - weird shadow darkness
Low angle - weird shadow darkness
No texture - pure matt
No texture - pure matt
Pure matt node with others disconnected
Pure matt node with others disconnected
Angle to horizon - no difference
Angle to horizon - no difference
Angle of light with Normals
Angle of light with Normals

Martini
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Location: Australia

Re: Terminator issue?

Post by Martini » Wed Oct 23, 2019 9:05 am

MarsThunder wrote:
Wed Oct 23, 2019 4:00 am
PS: normals are good and pointing out like they should.
It looks to me like the problem could be the geometry/normals. You have one huge face running across the object from left->right, then a 90-degree angle to the side face (and I assume, another face on the back?). If you smooth this (using "Shade smooth") it will have errors because there is not enough geometry on which to apply normals to handle that 90-degree turn. Could you try adding a loop cut on the right very close to the edge, and another one on the left? This should limit the change area to the face loop along the edge then.

You may be able to visualise this a bit easier by adding a SubSurf modifier. Take note of what happens to the curvature near the left and right edge. This is why you need "supporting faces" near the edge.

You could also try "Shade flat" and see if the problem goes away.
MarsThunder wrote:
Wed Oct 23, 2019 4:00 am
If a blend file is needed to test...let me know!
It might help. If you could. Just in case this was not the problem! :lol:
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Dade
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Re: Terminator issue?

Post by Dade » Wed Oct 23, 2019 9:08 am

Martini wrote:
Wed Oct 23, 2019 9:05 am
MarsThunder wrote:
Wed Oct 23, 2019 4:00 am
If a blend file is needed to test...let me know!
It might help. If you could. Just in case this was not the problem! :lol:
Yes, it is hard to say something without being able to check the scene.
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Martini
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Re: Terminator issue?

Post by Martini » Wed Oct 23, 2019 9:26 am

My description was probably hard to understand. Here is an image that might help a bit.

There are 3 cubes. I applied "Shade smooth" to each of them. Notice the left cube has quite a big shading error. You can see this is an issue even just in Blender's solid renderer; nothing to do with Lux.

The centre cube I have applied a Bevel to the top/bottom edges (using face select then Ctrl+B in edit mode). You could also do this using Inset. The appearance is better, but there is still an issue near the corners, because there is still a very long face across the edge from one side to the other.

The right cube has had every edge Bevelled (could also do this by adding Loop Cut and Slide several times). You can see the errors are not gone, but they are confined to a much smaller area. Subdivision would completely smooth these out correctly due to the supporting faces near the edges.

(Note than I used 2 segments and a bevel profile of 1.0)

Hope this helps! :D
Attachments
supporting-edges.png
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MarsThunder
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Re: Terminator issue?

Post by MarsThunder » Wed Oct 23, 2019 12:30 pm

Well, that certainly got rid of the issue. Turning shading to 'Flat' did it. What is interesting to me is that object is part of a scene I test renders with and it did not do that before (that I remember). I included a snip of a render from 2017 (I assume luxcore 2.0) and it is not noticeable. It is possible it was rendered with flat shading. Wait, I found the blend file and I'll be damned.....smooth shading was not tuned on. That is why I never noticed that before.

Thank you so much for that fast solution to something I didn't think of.
Attachments
Flat and no black shadow
Flat and no black shadow
LuxCore 2.0 version
LuxCore 2.0 version
Original Blend file was flat shaded
Original Blend file was flat shaded
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Marshall

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MarsThunder
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Re: Terminator issue?

Post by MarsThunder » Wed Oct 23, 2019 12:56 pm

Update..... Just subdividing the big planes and/or knife-ing the planes close to the edge does the trick. Now smooth shade can be turned on. Thanks for the info on the right-angle geometry issue! I wonder if that is one of the reasons the blue line colors are there for the straight edges - it certainly can let you see where issues could be in a complicated scene.
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Marshall

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Dade
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Re: Terminator issue?

Post by Dade » Wed Oct 23, 2019 1:59 pm

MarsThunder wrote:
Wed Oct 23, 2019 12:56 pm
Update..... Just subdividing the big planes and/or knife-ing the planes close to the edge does the trick.
Isn't there a blender tool named "edge split" to solve this kind of problems :idea:
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Martini
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Re: Terminator issue?

Post by Martini » Wed Oct 23, 2019 3:40 pm

Dade wrote:
Wed Oct 23, 2019 1:59 pm
Isn't there a blender tool named "edge split" to solve this kind of problems :idea:
Yep, that's another very good way to do it :lol:
MarsThunder wrote:
Wed Oct 23, 2019 12:56 pm
I wonder if that is one of the reasons the blue line colors are there for the straight edges - it certainly can let you see where issues could be in a complicated scene.
Blue edges are edges that you have marked "Sharp". Sharp edges are used by the Edge Split modifier that Dade mentioned to mark edges that you want it to split.

https://docs.blender.org/manual/en/dev/ ... split.html
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MarsThunder
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Re: Terminator issue?

Post by MarsThunder » Thu Oct 24, 2019 1:27 pm

Ahhh! Perfect example of how a Forum should work. Problem is solved and knowledge is spread!

Thanks again!
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Marshall

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