Artifacts with negative shear ???

Started by pclavett, August 30, 2020, 03:00:10 pm

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Hi all !
I am toying with doing a canyon based on several principles but mostly from the recent post by Geek At Play and having some difficulty in applying the displacement that I want appropriately.
If I set myself in the canyon, I want to displace in one direction on one side and the other on the other side.
I have figured out how to apply it on one side by using the X positive normal masking while I am looking towards 0 degrees.
That works and I applied it not completely to the top by inserting a Distribution shader......all well till then !
Then I wanted to open up the top of the canyon by inserting a negative X shear for the upper portions.....and it did but a very finite thickness at the very top did not follow and creates an artifact that can be seen in the picture included.
The same happens with negative lateral displacement !
It is as if a very thin shaving does not follow and according to the distribution shader, there should be no reason for it not being included.
I have included the file and image if any of you feel to examine this and see whether there is a way to fix this !
I appreciate your help and input as always !


This is just a wild guess but the normals on the top surface point toward Y, not X, and perhaps the shear shader has a problem with that.

I ran into similar issues while setting up my canal excavation scene. Matt's reply near the bottom of this page may shed some light on this. (Or perhaps not, but it's interesting either way.)

I'd use a displacement mask (SSS or hand-painted) in this case, I think.


I have tried to pick up the border with a painted shader of the rim no avail !
It still did not remove that artifact !
Good suggestion though !
Thanks for the input !
Take care !


August 30, 2020, 11:09:49 pm #3 Last Edit: August 30, 2020, 11:29:09 pm by Kadri
Move the distribution node with the twist and shear shader up and before the compute node.
Not sure if it is ok according to the scene you want but it looks like the artifact goes away.

Edit: Doesn't work i think.


If you want either side to bulge in, it's pretty simply done with a surface shader's offset. Just choose the right fuzzy zone and altitude. If you break this up by PF or mask you can have a variable bulge.