Converting coordinates system for FBX model in OpenGL

Question

I load FBX models using Autodesk FBX SDK2013.The models get rotated 90 degrees on X-Axis by default.

The SDK supplies this method :

FbxAxisSystem::OpenGL.ConvertScene(scene);

to perform axis conversion.But it doesn't work.Calling it changes nothing.Moreover,it seems that the FBX exporter uses OpenGL right hand sytem by default,at least that is what it says on import:

     FbxAxisSystem fbxAxis = scene->GetGlobalSettings().GetAxisSystem();

            if (fbxAxis != FbxAxisSystem::OpenGL)
            {
                      //....
            }

returns false. So I don't understand;if it is OpenGL (right handed system,why the models have Z axis as up? Is it the SDK bug?

Answer 1

I finally found the solution.Someone here actually said that the ConvertScene() doesn't affect the vertices array but sets node global/local matrices.With these we can then transform the node geometry or the vertices.

So here how it is done:

    FbxMatrix globalTransform = mesh->GetNode()->GetScene()->GetEvaluator()->GetNodeGlobalTransform( mesh->GetNode());
dvec4 c0 =  glm::make_vec4((double*)  globalTransform.GetColumn(0).Buffer());
dvec4 c1 =  glm::make_vec4((double*) globalTransform.GetColumn(1).Buffer());
dvec4 c2 =  glm::make_vec4((double*) globalTransform.GetColumn(2).Buffer());
dvec4 c3 =  glm::make_vec4((double*) globalTransform.GetColumn(3).Buffer());
glm::mat4 convertMatr =mat4(c0,c1,c2,c3);
convertMatr = inverse(convertMatr); //need to inverse otherwise the model is upside down

Then use convertMatr to transform mesh's vertices.Hope it will be helpful to anyone as Autodesk forum is not too much responsive.