Re: [Algorithms] CSG operations on textured meshes -- something better than CGAL?
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Re: [Algorithms] CSG operations on textured meshes -- something better than CGAL?
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From: Jon W. <jw...@gm...> - 2014-05-21 15:05:57
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> You are going to be distorting triangles in different ways depending on the overall shape of the mesh at any given point though. > If you just retain existing UV coordinates for the new vertices, the results will be... strange. I do this operation with some frequency in 3ds Max, and it works the way I expect there. The 3ds Max boolean (and proboolean) modifier behavior would be good enough for my purposes, although they do have some edge cases and limitaitons (a k a "bugs" :-) But I don't want to buy a copy of 3ds Max per server that will be running this code, not to mention I want to run the servers on Linux. So, does anyone know of any textured-triangle-mesh CSG library out there, free or paid for, that would work? Sincerely, jw Sincerely, Jon Watte -- "I find that the harder I work, the more luck I seem to have." -- Thomas Jefferson On Tue, May 13, 2014 at 10:07 PM, James Robertson <ja...@os...> wrote: > You are going to be distorting triangles in different ways depending on > the overall shape of the mesh at any given point though. If you just > retain existing UV coordinates for the new vertices, the results will > be... strange. > > Consider the case where a convex region meets a concave one. One side of > the triangle will be slightly expanded, while the other side will be > contracted. Of course you know your input data better than us, so maybe > such distortions are acceptable or won't be noticeable, but they will be > there. > > > > On 14/05/2014 01:41, Jon Watte wrote: > > I don’t believe you will be able to use your existing uv values with the >> mesh that results from this csg operation > > > The operations I want to do are rigid and well conditioned and do not > stretch or generate new surfaces compared to the input meshes. They may > invert the winding of triangles, though (so normal maps would have to be > flipped) in the case of a cut-out. > I also need to preserve vertex bone weighting, too... something that can > preserve UV should be able to preserve that, too. Worst case, I put in a > vertex ID value in the UV channel and loop up the other parameters based on > that. > > So... no general purpose parameterized trimesh CSG library available? > > Sincerely, > > jw > > > > > > Sincerely, > > Jon Watte > > > -- > "I find that the harder I work, the more luck I seem to have." -- Thomas > Jefferson > > > On Thu, May 8, 2014 at 12:28 PM, Chris Green <cg...@va...>wrote: > >> I don’t believe you will be able to use your existing uv values with >> the mesh that results from this csg operation – it has a different >> topology, and there will be changes in the ratios of the areas of different >> parts of the model, with really bumpy areas of the mesh being smoothed out, >> etc. You’ll even have brand new areas emerge that don’t have corresponding >> areas on the original model, as holes are filled in, etc. >> >> >> >> What might work better is to just do the csg operation and generate a uv >> atlas for the resultant mesh. You can then generate a new texture map for >> this uv parametization by sampling from the original one, in a similar >> manner to the way in which people produce bumpmaps mapping the normals of >> highly tessellated models onto low-detail models. >> >> >> >> >> >> >> >> *From:* Jon Watte [mailto:jw...@gm...] >> *Sent:* Thursday, May 08, 2014 11:08 AM >> *To:* Game Development Algorithms >> *Subject:* [Algorithms] CSG operations on textured meshes -- something >> better than CGAL? >> >> >> >> I have a triangle mesh composed of many submeshes with different >> textures/materials. This mesh may not be a 2-manifold -- it may have open >> edges. Typical game art. >> >> >> >> I now want to create a 3mm thick shell of this mesh. As an approximation, >> taking each triangle, and extrude it back along the normal of each vertex, >> and union all of those generated chopped pyramids would be an approximation >> of what I want. If I do literally that, and self-union the result, then >> that should resolve the self-intersection problems I'll run into along >> narrow sharp creases etc. >> >> >> >> I can't find any library to do this, though. CGAL has some fairly robust >> functions on NEF polyhedra, but those polyhedra don't seem to allow >> parameterization (which is academic speak for texture coordinates that may >> have discontinuities across edges.) >> >> >> >> So, what are some robust CSG libraries available that work on such >> game-style meshes, preserving texture coordinates? >> >> >> >> (And actually, I don't have one such mesh; I have > 120 million such >> meshes, so a by-hand or even script-the-Max-shell-modifier solution is >> unlikely to work. I do have hundreds of Linux servers at my disposal, >> though.) >> >> >> >> Sincerely, >> >> Jon Watte >> >> >> -- >> "I find that the harder I work, the more luck I seem to have." -- Thomas >> Jefferson >> >> >> ------------------------------------------------------------------------------ >> Is your legacy SCM system holding you back? 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