Vertex order

Hello,

I have the vertices and index data for a model. But some of the faces do not get rendered. After experimenting for a while, i have found that the vertex order is causing the issue. To demonstrate the behavior, here is a small code snippet that i am trying with "OculusRoomTiny" sample. In this code, the vertices correspond to a plane with +Y as its normal and vertices are as shown.

2 3
x--------------x
|--------------|
|--------------|
x--------------x
0 1

If the indices of the two triangles are provided as 2,1,0 2,3,1 - it works.
If the indices of the two triangles are provided as 0,1,2,2,1,3 - it does not work.

But considering that the face has a normal of 0,1,0, I am expecting it to work with 0,1,2,2,1,3 as the indices.

Any suggestion on how the vertex order is determined ?

Here is the code snippet that can be included in "OculusRoomTiny" sample for testing. I haven't done any other change to the sample other than stopping the model[0] from getting moved so that i can see the plane.

void Model::AddCustomSolid( Color c)
	{
	   Vector3f Vert[][2] =
	   {
		    // y = 1 Top face with normal 0,1,0
			Vector3f(1.0, 1.0, 1.0), Vector3f(1.0, 1.0), 
			Vector3f(1.0, 1.0, 0.0), Vector3f(1.0, 0.0),
			Vector3f(0.0, 1.0, 1.0), Vector3f(0.0, 1.0),
			Vector3f(0.0, 1.0, 0.0), Vector3f(0.0, 0.0), 
		};

	    int numOfIndices  = 6;
	    int numOfVertices = 4;

	    // Works
        uint16_t CubeIndices[] = 
		{ 
			 2, 1, 0, 
			 2, 3, 1,
		};
		//*/

		//// Does not work
		//uint16_t CubeIndices[] = 
		//{ 
		//	 0, 1, 2,
		//	 2, 1, 3, 
		//};
        
        for(int i = 0; i < numOfIndices; i++)
            AddIndex(CubeIndices[i] + (uint16_t) numVertices);

        for(int v = 0; v < numOfVertices; v++)
        {
            Vertex vvv; 
			
			vvv.Pos = Vert[v][0];  
			vvv.U = Vert[v][1].x; 
			vvv.V = Vert[v][1].y;
			vvv.C = c;

            AddVertex(vvv);
        }
	}

Thank you

Regards,
Ram