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 <cgreen@valvesoftware.com> 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:jwatte@gmail.com]
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? Join Perforce May 7 to find out:
&#149; 3 signs your SCM is hindering your productivity
&#149; Requirements for releasing software faster
&#149; Expert tips and advice for migrating your SCM now
http://p.sf.net/sfu/perforce
_______________________________________________
GDAlgorithms-list mailing list
GDAlgorithms-list@lists.sourceforge.net
https://lists.sourceforge.net/lists/listinfo/gdalgorithms-list
Archives:
http://sourceforge.net/mailarchive/forum.php?forum_name=gdalgorithms-list



------------------------------------------------------------------------------
"Accelerate Dev Cycles with Automated Cross-Browser Testing - For FREE
Instantly run your Selenium tests across 300+ browser/OS combos.
Get unparalleled scalability from the best Selenium testing platform available
Simple to use. Nothing to install. Get started now for free."
http://p.sf.net/sfu/SauceLabs


_______________________________________________
GDAlgorithms-list mailing list
GDAlgorithms-list@lists.sourceforge.net
https://lists.sourceforge.net/lists/listinfo/gdalgorithms-list
Archives:
http://sourceforge.net/mailarchive/forum.php?forum_name=gdalgorithms-list




This email is free from viruses and malware because avast! Antivirus protection is active.