Bugs in TexturedMesh affine_transform

[Jingyu6]

Hi simple-3dviz team,

Recently I've been using this great lib but encountered the problem when I want to apply a rotation on a textured mesh. I tried loading an obj file with TexturedMesh and Mesh:

textured_mesh = TexturedMesh.from_obj_file(obj_path)
raw_mesh = Mesh.from_file(obj_path)

(TexturedMesh.from_file also has the same problem)

Then I applied the following rotation on these objects like

R = np.zeros((3, 3))
R[0, 0] = np.cos(theta)
R[0, 2] = -np.sin(theta)
R[2, 0] = np.sin(theta)
R[2, 2] = np.cos(theta)
R[1, 1] = 1.

textured_mesh.affine_transform(R=R)
raw_mesh.affine_transform(R=R)

Finally, rendered them to get the following:
(Textured mesh)

(Raw mesh)

It looks like the vertices and faces of the textured mesh all get messed up whereas the mesh without textures looks fine. Here's a textured mesh loaded without applying any rotations as a reference:

So I guess there might be some problems when the lib handles rotation for textured meshes. Due the data privacy, I can't share the model obj that I used. Can I get some help with this? Great thanks in advance!

Best,
Jingyu

[Jingyu6]

It seems to me that the problem with affine_transform for textured mesh is that it changes the vertices directly whereas methods like rotate_along_axis and rotate_x/y/z will change the model_matrix instead. The latter ones work perfectly well so I think there needs to be some fix for TexturedMesh.affine_transform.

Another point during code inspection: back-face culling is done in the fragment shader, which I'm not sure if it is the good way to do so.