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trentfaris242

Assimp importing incorrect number of textures?

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Hey all,

I've started using Assimp in my project, and I've run into an odd issue.

I've got a simple textured cube I've created in Blender and exported to OBJ/MTL format. Here they are (pretty short):

cube.obj
[SPOILER]
# Blender v2.75 (sub 0) OBJ File: ''# www.blender.orgmtllib cube.mtlo Cubev 0.500000 -0.500000 -0.500000v 0.500000 -0.500000 0.500000v -0.500000 -0.500000 0.500000v -0.500000 -0.500000 -0.500000v 0.500000 0.500000 -0.499999v 0.499999 0.500000 0.500000v -0.500000 0.500000 0.500000v -0.500000 0.500000 -0.500000vt 0.000000 0.000000vt 1.000000 0.000000vt 1.000000 1.000000vt 0.000000 1.000000vn 0.000000 -1.000000 0.000000vn 0.000000 1.000000 0.000000vn 1.000000 0.000000 0.000000vn -0.000000 0.000000 1.000000vn -1.000000 -0.000000 -0.000000vn 0.000000 0.000000 -1.000000usemtl Material.001s offf 1/1/1 2/2/1 3/3/1f 8/2/2 7/3/2 6/4/2f 5/2/3 6/3/3 2/4/3f 6/2/4 7/3/4 3/4/4f 7/2/5 8/3/5 4/4/5f 1/2/6 4/3/6 8/4/6f 4/4/1 1/1/1 3/3/1f 5/1/2 8/2/2 6/4/2f 1/1/3 5/2/3 2/4/3f 2/1/4 6/2/4 3/4/4f 3/1/5 7/2/5 4/4/5f 5/1/6 1/2/6 8/4/6
[/SPOILER]

crate.png
[SPOILER]
# Blender MTL File: 'None'# Material Count: 1newmtl Material.001Ns 96.078431Ka 0.000000 0.000000 0.000000Kd 0.640000 0.640000 0.640000Ks 0.500000 0.500000 0.500000Ni 1.000000d 1.000000illum 2map_Kd crate.png
[/SPOILER]

When I call the ReadFile function on the OBJ file, I am calling with 2 flags: aiProcess_Triangulate and aiProcess_JoinIdenticalVertices. The scene seems to be properly created from this call. I can get the vertices, UVs, normals, and indices correctly and render them just fine. The issue is with the materials. When I call scene->mNumMaterials it returns 2 even though I only have 1 texture used in this mesh. The first loads the texture successfully, but then the second is some "ghost" material (or one that I'm unaware of), and it is throwing my mesh off.

Am I missing some flags that should be present or operating with some false assumptions that are causing me to have issues? If anyone could help me understand more about what's going on here that would be great! Thanks!

UPDATE: Using a workaround (basically just ignoring the first material), I can get it to work perfectly fine, but that still leaves my original question. Every time Assimp creates a scene it seems to generate a material at index 0 that is NULL. In other words, if my OBJ has 2 materials in it, the mesh will have 3, but the first will always be NULL. Does anyone know the reasoning behind this? Edited by trentfaris242

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