Re: [Algorithms] CSG operations on textured meshes -- something better than CGAL?

[Jon W. <jw...@gm...>]

>
> 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
>
>
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