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displacement artifacts?

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displacement artifacts?

Unread postby trantor » Sun Jan 24, 2021 11:27 am

Hello,

I am running into some issues with displacement on a referenced alembic ground plane used as a terrain.

As you can see from the screenshots, when using displacement settings on the geo, the primitive / individual face edges start to show up. The higher I set the tesselation, the more pronounced they get - almost like the additional edges do sharpen the base primitive edges (similar to when you add edgeloops to hold an edge on subdivision surfaces). When I do a similar setup on a native clarisse polygrid, those "artifacts" do not appear.

On the referenced alembic they disappear when I enable subdivision surface.

Which leads me to another question, whether its better to use displacement or subdivision or both? Of course if you need subdivision features like creased edges subd is the way to go. But what are the benefits of using either one or the other, since they both seem to add tesselation which can be used for displacement.

Thanks.

Felix
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Re: displacement artifacts?

Unread postby aaute » Mon Jan 25, 2021 11:19 am

Hi,

you should use the Tessellation with Bump (mode by default). In this case you keep the information of the geometry underneath and when you tessellate you keep the smoothing. If you use Tessellation only, each faces are subdivided flat and you loose the continuity, resulting to this faceted look. If you add the same displacement on a polysphere you can really see the effect.

Better to use Tessellation with Bump or subdivision in your case. https://clarissewiki.com/olympus/displacements.html shows you the result you should expect with the different options.

Cheers
Aymeric
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Re: displacement artifacts?

Unread postby trantor » Mon Jan 25, 2021 2:01 pm

Hi Aymeric,

thanks for helping out on this. Your example with the sphere really made it obvious!

I was playing around with tessellation settings before and noticed that with bump it goes away, but since bump also introduced a lot of fine detail, which in this case I did not want, I set it to the option without bump.

Also I thought the smoothing options below would take care of normal smoothing like the bump obviously does in the tessellation settings? But it looks like it does not, since swapping through those settings there seems to be no visible change.

Since those issues do not show up when I use subdivision instead, are there any disadvantages to favor subd over span count settings? I assume raising span count is more efficient, since it does not increase primitive count?


Another question regarding the bounds setting. In the docs you linked to it states that bounds should be set to "maximum extension of the displacement texture". Is there a way to figure out this extension or is it something to be eyeballed? Also if I remember correctly, in some tutorials this value has been set to the size of the displaced geometry. What is the proper way to get this setting right?


Cheers,

Felix
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Re: displacement artifacts?

Unread postby Akam » Fri Jan 29, 2021 2:14 pm

Hi Felix,

to your last point: Displacement bounds setting

Imagine you have a grid that you want to displace via texture (e.g. to built a terrain)
The height of this terrain will be determined by the Front Value of the displacement shader and this value is also the "maximum extension of the displacement texture" so you have to enter same value to the bound.
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Re: displacement artifacts?

Unread postby trantor » Sat Jan 30, 2021 9:00 am

Hi Akam,

thanks for your explanation. I tested this on a couple of objects and it seems to work perfectly fine. No more guess work, yeah ;)
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