Rendering problem of triangles

Hi Burak,

could you please attach some pictures to give us better idea?

Anyway, check how this function is defined for non-deformable tatrahedron
[1]

cheers
Jan

[1]
http://bazaar.launchpad.net/~yade-pkg/yade/git-trunk/view/head:/pkg/dem/Tetra.cpp#L995

2013/12/9 burak er <email address hidden>

> New question #240509 on Yade:
> https://answers.launchpad.net/yade/+question/240509
>
> Dear Yade-Dev,
>
> I have problems with rendering of faces of my deformable tetrahedron class
> that I defined within yade. Within deformable tetrahedrons, each vertex is
> defined in a list and each face of the deformable tetrahedron also defined
> in another list including it's connected vertex indices. I create
> tetrahedrons by importing mesh from a gmsh file where its node numbering
> order is given in gmsh's manual.
>
> When I try to give opengl the normal of each face with the calculating
> method given here[1] or even calculating it with the node numbering as
> given in the user manual of gmsh , I see the coloring difference of the
> tetrahedrons faces. My drawing function of the deformable elements can be
> found here[2].
>
> So I want to ask; What may cause the difference of the colors of the faces
> of tetrahedron with the code given at[2]? Do you suggest a better way to
> draw a tetrahedron?
>
> [1]
> http://math.stackexchange.com/questions/183030/given-a-tetrahedron-how-to-find-the-outward-surface-normals-for-each-side
> [2]
> https://github.com/burak-er/trunk/blob/master/pkg/dem/deformablecohesive/Gl1_DeformableElement.cpp
>
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Hi Jan,

You can see an example capsule mesh that I have created[1]. The color for the whole tetrahedrons should be red, but you can see brown, grey and the nearly the black ones. The problem exist for the internal faces of the tetrahedrons[2].

I could not identify the problem.

[1]http://i.imgur.com/Fts3MGY.png
[2]http://i.imgur.com/ljlEYy7.png

Hi,

I guess the problem is in the direction of facet's normal. It depends on the
node numbering: clockwise or counterclockwise.

Anton

2013/12/9 burak er <email address hidden>:
> [1]http://i.imgur.com/Fts3MGY.png
> [2]http://i.imgur.com/ljlEYy7.png

Hi Anton,

Do you suggest a way for the calculation of the normals for the faces of a tetrahedron? I think the method that I gave at the first message has some problematic situations. But, I also used the node numbering sequence at the gmsh manual[1]. Still had the problem.

Thank you in advance.

[1]http://www.geuz.org/gmsh/doc/texinfo/#MSH-ASCII-file-format

To get rid of the (anti/)clockwise numbering question, you can display both faces (GL_FRONT_AND_BACK*).

*https://www.opengl.org/sdk/docs/man/xhtml/glPolygonMode.xml