[ishook]

Hey guys, I'm running into a problem with displacement on this chair I have. The mesh is pretty basic, the only material currently on the object is the displacement. For whatever reason it's rendering as a checkerboard, one that follows the lines of the mesh. Is there something I can do to my mesh to make it not do this? I tried rendering the same material on a sphere and it was fine. There must be something wrong with the mesh but I can't figure it out. I even exported as obj, imported. I tried importing and exporting from rhino, nothing cleans it of this error. I tried fixing normals, smoothing. nothing works.

Can anybody offer a suggestion?

[Mihai]

I think the only thing that can help is raising the precision, but it would have to be raised a lot. That displacement map is very fine compared to the underlying geometry. I'd suggest in this case to use a normal map instead, it will still look pretty convincing.

[Hervé]

yes Normal map could cure it... these squares you see are in fact underlying geometry not smoothing ... (your polygons..)

OR... subdivide your base mesh to death to have tiny polygons (don't worry Maxwell can handle Millions+ polys..)

BTW, Increasing precision will have normally no effect...

hope this helps..

[ishook]

I tried subdividing one more level and all it did was make the checker squares that much smaller, but still there. I had an identical map of 2.5x the resolution and I got the same squares. It was 2500x2300 or something like that. I'm going to try the Snapshot plugin (in 3D studio) but thats the only other thing I think I can try. I was looking for a way to explode all my polys into seperate objects but I can't find a method to do that. I was going to weld and retry, thinking it would do a better job the next time around.

I might just have to use a normal map, but it really isn't 'there' in terms of reality.

[Hervé]

when I said subdivide.. I meant... to death.. hehe ... I know your problem... I had the same... so I know...

... In 2.0, the bump map is so good.. you won't have problems..

but right now here is your problem...

(from Tom's explanation)

The smoothed look of polygons (even without bump) is a mathematical estimation. In fact, it's something faked on the fly when rendering. Because, when shading smooth, we're painting tonalities those are physically non-existing on given exact geometry. Doing this in an unbiased (where energy conservation and continuity is a "must") engine conflicts with this fake called "smoothing". So, the smooth look we all used to see in biased engines are not matching with unbiased smoothing. What's related with bump and nm about this? Easy. Bump and normal mapping are two other fake surface shading methods which directly uses surface normals in calculation. Therefore, they have to work in good relation with usual surface smoothing. But with the limitation of initial smooth shading of polygons, they quickly tend to fail because they try to fake a more frequent pattern and it breaks the smooth flow quickly. So, if the frequency of detail in bump is finer than the frequency of vertex density on the mesh surface, it overrides initial smooth approximation. When loose, it would look OK. "Loose" means you have a denser mesh or you have a less frequent (less than vertex density) detail in bump. In addition to this, the desired height of bump plays a negative role here. The more height in bump means the more perceivable faceting.

[Bubbaloo]

In my tests, this problem is attributed to non-uniform sized polygons. If you have really tiny polygons and large ones on the same mesh, this is the result. I've seen this happen with displacement grass on large landscapes too. I wish there was a "cookie cutter" command to slice a mesh into uniformly sized polygons based on the smallest polygon present on the mesh... Subdividing the mesh or using higher precision really doesn't help in this situation because the discrepancy in polygon size will always remain.