Hi Dave, it's a display glitch caused by the display mesh having a low density of triangles in that area.
Shaded surfaces are actually drawn on the screen by drawing triangles. When there are enough triangles it gives the illusion of smoothness but when there are not many triangles following a curved path the illusion kind of breaks down and you can see the triangulated silhouette for the shaded part of the display.
Curves are drawn using a different method that dynamically adapts the line density to the current view so that's why the edges look better there. It's unfortunately much more processing and therefore expensive performance-wise to do the same to surfaces. So surfaces get a triangulation that adapts somewhat to the object but not to the current view.
This problem of the surface display looking rough tends to happen in areas that have relatively slight curvature over a larger span of the object like your object here.
There isn't anything actually wrong with the object, it's just only a cosmetic problem with the display. If you export out to a polygon mesh format you can generate a higher density mesh at that time for the export. Also if you export out to PDF or AI formats, the shaded surface display there does have a view adaptive refinement because when you're doing an export the balance is higher on the quality side of things than the speed side. LIke for example when you're doing an export if it takes 20 seconds to generate something it's ok at that point but taking 20 seconds for every redraw in a viewport while you are working is not ok.
It's just something to ignore - you may see a couple of different kinds of display artifacts like this in the viewport display because the viewport display engine is more tuned to doing things quickly and can cut corners in some situations to get that speed.
I have some ideas for improving this in the future like maybe starting with a rough mesh to get an initial display quickly but then generating higher density ones on a background thread. This will be tricky to set up though with various things like making sure things doing break if an object is deleted while the background thread is still working with it so it's something that will take time to work on and I don't know exactly when I'll be able to get to it.
- Michael
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