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

[Graham R. ARA/S. <gr...@ar...>]

Components of the IntegrityWare SOLIDS++ commercial middleware may be useful. For example:

http://www.integrityware.com/meshlib.html

Not sure how they handle interpolating vertex attributes, though. They might support a user-provided function for that.

Beyond that, we use Spatial’s ACIS library for some quite complex CSG work. This adds another level of cost and complexity through, being primarily used in the CAD industry. It does support non-manifold topology, regularized and non-regularized solids, provides built-in functions to do operations such as extruding or offsetting a sheet into a thickened solid, geometry healing, etc. ACIS is extremely flexible in the way you can attribute intermediate surfaces and edge lists that arise during the evaluation of CSG ops. And there are the ACIS competitors…Parasolid, Granite, Open Cascade (assuming these others still exist…my knowledge of solid modeling kernels is slightly stale now).

Graham

From: Eric Haines [mailto:eri...@gm...]
Sent: Wednesday, May 21, 2014 11:39 AM
To: Game Development Algorithms
Subject: Re: [Algorithms] CSG operations on textured meshes -- something better than CGAL?

I'd certainly like to know, too. MeshLab might have one hiding in its bowels, but I haven't looked hard enough yet. MeshMixer looks super-cool, but appears to be just an application, not a library.

On Wed, May 21, 2014 at 11:05 AM, Jon Watte <jw...@gm...<mailto:jw...@gm...>> 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.

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...<mailto: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...<mailto: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...<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