Something indeed doesn’t look right in this extrusion result, maybe an error in computing the tangent directions (U/V) on a flat SubD.
Could you clarify a few things for me:
In which SubD display do you expect the offset to be correct? I see both display modes in your images. If the vertices are offset at a constant distance in the sharp display then their distance in the smooth display mode might not be the same (and this issue stays if the order is reversed). Rhino gives priority to the limit surface here, computing new vertices positions so that the smooth display is “correct”.
Are you aware that even if the offset is correct at the vertices, it might not be true all along the edge? I.e., if vertices are at a constant distance from each other in smooth display, the distance between points on the edge might still vary a little bit? It looks like you are trying to design fonts using SubDs and I’m not sure what the requirements are on something like this.
It is all planar. I either work in top or front view.
The ‘smooth’ display is usually off but I was afraid it took priority.
I always model in box/sharp display and then refine in smooth. Yes, I use SubDs to create graphic design and 3D logos in many cases. A number of other SubD modelers, Modo for instance, offsets a consistent width doing this type of operation. Can we have a choice? A toggle of some sort.
Very nice images @PaulS! Thank you for explaining how you work; a few clarifications below on what I meant in my previous message:
It’s not so much which display has priority to look nicer, it’s what geometry the commands are working with as reference.
Like with NURBS, the SubD control polygon’s exact position does not really matter. That’s just where the control points/vertices happen to be for the surface to have its current shape. So most commands, like Extrude, will act on the actual surface, not on the control polygon.
I just tried it, it looks like Modo does a constant width offset of the control polygon edges. In Modo, measuring the offset on the subdivided surface, the distances you are measuring in your first image are also not constant. It does look better because this constant offset of the control polygon is better than what we are doing in this case.
I think we need to fix the current boundary SubD edge extrusion tool (for planar edges?), but I don’t see a need for a constant offset tool in both the control polygon space and the SubD space so far.
Thanks Pierre, for giving this some attention…and on my work.
Having the SubDs in Rhino is a god-send for me as I work with SubDs and Nurbs in unison. Previously I would work in Modo, export to Fusion 360 and then export to Rhino as nurbs conversion. So nice to be able to stay in Rhino.
A few operations are a little more painful in Rhino as compared to Modo but I get them done. It can be frustrating to do a boundary extrude from planar edges and then have to go though each and every created face to even things up so having some attention on this from you is very appreciated.
