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FBX SDK Normal parsing problem

General and Gameplay Programming Programming

Started by eee August 07, 2014 10:38 AM

5 comments, last by eee 9 years, 8 months ago

eee

271

Author

August 07, 2014 10:38 AM

I know there are a couple of threads here discussing this issue, but unfortunately I wasnt able to find a solution to the problem Im having.

Using the fbx sdk I can parse vertex coordinates and indices. I can draw meshes correctly but now am trying to implement very rudimentary lighting. For this I obviously need to read normals and doing so for a simple cube which has a side length of 1, 8 vertices and 36 indices. When using the fbx sdk my normals for the cube are parsed like this:


else if (fbxNormal->GetMappingMode() == FbxGeometryElement::eByPolygonVertex){
if (fbxNormal->GetReferenceMode() == FbxGeometryElement::eDirect){ // this is where the if is true, nowhere else
vertices[i].nor = XMFLOAT3(static_cast<float>(fbxNormal->GetDirectArray().GetAt(i).mData[0]),static_cast<float>(fbxNormal->GetDirectArray().GetAt(i).mData[1]),static_cast<float>(fbxNormal->GetDirectArray().GetAt(i).mData[2]));
}

I understand that to have lighting for a cube I should have 3 normals per vertex but right now when doing some checks the code runs in the code block specified above (the if statements). When I check the vertices I see this:

The normals seem very weird, am I exporting it wrong from 3ds?

My very simple lighting shader looks like this:


float4 diffuse = light.diffuse;
float3 finalColor = diffuse*light.ambient;
finalColor += saturate(dot(-light.dir,input.nor)*light.diffuse*diffuse);
return float4(finalColor,diffuse.a);

This is what the result looks like:

http://postimg.org/image/nh8vjyfep/full/

http://postimg.org/image/rj2s4fbm3/full/

Very odd :(

Buckeye

10,754

August 07, 2014 11:57 AM

First, I'm not familiar with FBX, so I can't help you there.

The normals seem very weird

Actually, they appear to be correct for the two cube faces facing -Z and +Z. If vertices 0-3 are indexed to form the -Z facing quad, the normals should be (0,0,-1). Similar for vertices 4-7, facing +Z. For the other 4 faces, the normals need to face in the same direction as the face - i.e., for the quad facing +X, norm = (1,0,0), etc.

You can calculate the face normal using the cross product of two of the three vectors forming one of the face triangles.

With regard to the images, it depends on what axes are facing which direction. However, if the light direction is along a cube diagonal, it appears correct for the normals listed above.

Please don't PM me with questions. Post them in the forums for everyone's benefit, and I can embarrass myself publicly.

You don't forget how to play when you grow old; you grow old when you forget how to play.

eee

271

Author

August 07, 2014 07:39 PM

The light is defined by XMFLOAT3(0,0,1), which should shine right into the +Z axis (note im negating the value in the shader, so that shouldnt be the issue). All im doing is rotating the cube along the Y axis, the logical outcome should be: the side of the cube facing the light source (the camera, really), should gradually lit up when cube is rotated.

Trying out the normals/lighting shader on a porsche panamera, I get this result:

http://postimg.org/image/ze4q9velr/full/

http://postimg.org/image/ha1pp8gxb/full/

http://postimg.org/image/cdphhxvoj/full/

Does this mean my lighting calculations are wrong, or that the normals are wrong? Using 3ds to export to .fbx and then using fbx sdk to read the mesh data.

Endemoniada

431

August 08, 2014 01:42 AM

Hi,

I pulled this out of my code that I'm pretty sure is working fine. If you need more just let me know.


...
...
int vertexId=0;

// for each polygon
for(int j=0;j<mesh->GetPolygonCount();j++){

 if(mesh->GetPolygonSize(j) == 3){
 
  // for each vertex
  for(int k=0;k<3;k++){
 
   // extract normal
   for(int l=0;l<mesh->GetElementNormalCount();l++){
 
    FbxGeometryElementNormal* leNormal=mesh->GetElementNormal(l);
 
    if(leNormal->GetMappingMode() == FbxGeometryElement::eByPolygonVertex){
     if(leNormal->GetReferenceMode() == FbxGeometryElement::eDirect){
      FbxVector4 normal=leNormal->GetDirectArray().GetAt(vertexId);
      buffer->nx=(float)normal[0];
      buffer->ny=(float)normal[2];
      buffer->nz=(float)normal[1];
     }
    }

   }

   buffer++;
   vertexId++;

  }

}

// it will fill in user-supplied buffer, I swap y and z

eee

271

Author

August 08, 2014 07:59 AM

This is how i get the vertex positions:


v.pos = XMFLOAT3(static_cast<float>(mesh->GetControlPointAt(i).mData[0]),static_cast<float>(mesh->GetControlPointAt(i).mData[1]), static_cast<float>(mesh->GetControlPointAt(i).mData[2]));

and later on the normals


else if (fbxNormal->GetMappingMode() == FbxGeometryElement::eByPolygonVertex){
if (fbxNormal->GetReferenceMode() == FbxGeometryElement::eDirect){ // right here
vertices[i].nor = XMFLOAT3(static_cast<float>(fbxNormal->GetDirectArray().GetAt(i)[0]), static_cast<float>(fbxNormal->GetDirectArray().GetAt(i)[1]), static_cast<float>(fbxNormal->GetDirectArray().GetAt(i)[2]));
}

I also tried to swap the y and z axis but then the models appear completely black.

I do this before the parse:


	FbxAxisSystem axisSystem = FbxAxisSystem::eDirectX;
	if (scene->GetGlobalSettings().GetAxisSystem() != axisSystem){
		axisSystem.ConvertScene(scene);
	}

It would seem we are doing the same thing but for some odd reason my lighting is completely off.

Maybe the problem is with understanding how vertex indices and normals relate? As of now I just have a loop

from i=0 to verticecount and just plug in i to any of the getter functions. Maybe i need to somehow take account some indices?