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# UV problem with FBX and DX11

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7 replies to this topic

### #1JacobM  Members

Posted 25 October 2013 - 10:12 PM

Hello All!
Came by here today hoping somebody has some experience loading models into DX11 using the FBX SDK. I am
having a weird problem when I load in my texture coordinates. On some models, they render correctly while on others, they render with the "U" flipped. An example below:

The space ship is rendered correctly, while the planet texture is flipped. Both are using the same code to load them in, the only difference is that I am sending in different strings for where to fetch the file from.

I load in the vertices from FBX in the following manner:

	int counter = 0;
//Loop through the polygons
for (int p = 0; p < fbxMesh->GetPolygonCount(); p++)
{
//Loop through the three vertices within each polygon
for(int v = 0; v < fbxMesh->GetPolygonSize(p); v++)
{

const int controlPointIndex = fbxMesh->GetPolygonVertex(p, v);

VertexStruct vS;
vS.position = FBXD3DVector3(fbxMesh->GetControlPointAt(controlPointIndex));

FbxVector2 tex;
bool isMapped;
fbxMesh->GetPolygonVertexUV(p, v, lUVSetName, tex, isMapped);
vS.uv = D3DXVECTOR2(tex[0], -tex[1]);

FbxVector4 norm;
fbxMesh->GetPolygonVertexNormal(p, v, norm);
vS.normal = D3DXVECTOR3(-norm[0], -norm[1], -norm[2]);

m_Vertices.push_back(vS);

m_Indices.push_back(static_cast<unsigned int>(counter));

counter++;
}

}



Tried looking on the FBX forums but had no luck. I could hard code them individually but I was looking to create a system where all my resources are loaded. Any help would be greatly appreciated. Thanks!

### #2MJP  Moderators

Posted 25 October 2013 - 10:32 PM

This is typical when using content from DCC packages in D3D. D3D specifies that V = 0 is the top of the texture and OpenGL specifies that V = 0 is the bottom, so you usually have to flip the V coordinates (and the bitangents!) when generating meshes for D3D.

### #3JacobM  Members

Posted 25 October 2013 - 10:57 PM

Thanks for the reply. Yes I understand that...however my problem seems to be with the 'U' coordinates. The planet is flipped ( so you have Asia on the western hemisphere and the Americas on the east.). The mesh was just a simple sphere that I exported from 3Ds Max, applied a mesh modifier, applied a texture to it and unwrapped it. The models I downloaded from TurboSquid. I tried 2 different artists and both loaded correctly. The same happened when I tried it on a cube.

Edited by JacobM, 25 October 2013 - 10:59 PM.

### #4N.I.B.  Members

Posted 26 October 2013 - 01:07 AM

Is your coordinate system handness coorect? 3DS Max is right-handed, while DX if left-handed.

If you export it as RHS, then in DX all of your triangles will be facing inward, causing back-face culling to cull the wrong triangles. Which means you are seeing the inside of the sphere, creating the apperance of U coordinate mirroring.

You can test this theory by rotating the sphere - if I'm correct, then it will appear to rotate in the wrong direction.

### #5imoogiBG  Members

Posted 26 October 2013 - 06:35 AM

Check you export settings. Probablly the problem is in the UVW mapping. Use the UVW modifination(if you're using 3ds max) and specify the mapping type. If you drag and drop the texture the default the mapping generated will be OGL style(not shure im always using UVW modifier). You can tell 3ds max to generate fliped UVs

### #6MJP  Moderators

Posted 26 October 2013 - 11:52 AM

Thanks for the reply. Yes I understand that...however my problem seems to be with the 'U' coordinates. The planet is flipped ( so you have Asia on the western hemisphere and the Americas on the east.). The mesh was just a simple sphere that I exported from 3Ds Max, applied a mesh modifier, applied a texture to it and unwrapped it. The models I downloaded from TurboSquid. I tried 2 different artists and both loaded correctly. The same happened when I tried it on a cube.

### #7JacobM  Members

Posted 26 October 2013 - 12:39 PM

Satanir:

This is what I originally thought as well. However culling was turned on and it was culling the correct triangles. i inverted the mesh in 3Ds max and it indeed fixed the texture. But now i was seeing inside of the sphere. Also, if that was the case then i assume the spaceships textures would have been inverted as well, but they come out just fine.
But I am sure that the sphere is being drawn correctly so I am not understanding why I am getting such mixed results.

imoogiBG:
I have used the UV unwrap, and the UV Xform. i even tried the UV Map modifier as u suggested. And you're right I could just flip the texture backwards in 3Ds this way it comes out correctly when I load it, but I would really like to get to the source of this. Not sure what other problems I may run into down the line. But I just find it weird that complex objects come out correctly while standard primitives like cubes and spheres come out like this. I think that may play some kind of role in this.

### #8JacobM  Members

Posted 26 October 2013 - 01:18 PM

Satanir, I guess u you were right, feel like a dunce now.

After a little reading I found all I had to do was switch the position Y and position Z of the verts like so:

FbxVector4 position = fbxMesh->GetControlPointAt(controlPointIndex);
vS.position = D3DXVECTOR3(position[0], position[2], position[1]);

FbxVector2 tex;
bool isMapped;
fbxMesh->GetPolygonVertexUV(p, v, lUVSetName, tex, isMapped);
vS.uv = D3DXVECTOR2(tex[0], -tex[1]);

FbxVector4 norm;
fbxMesh->GetPolygonVertexNormal(p, v, norm);
vS.normal = D3DXVECTOR3(-norm[0], -norm[2], -norm[1]);


Thanks for the help. Hopefully this will also help someone else with the same issue.

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