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Extracting Vertices and Triangles from an XNA Model

jwatte's picture
July 11, 2008 - 23:38 — jwatte

Here is some code that lets you extract the vertices and indices from a loaded XNA Model. You do not need to use any special processor, such as the JigLibX VertexProcessor or some derivative of the ModelProcessor -- it works straight out of the box!

    struct TriangleVertexIndices {
      public int I0;
      public int I1;
      public int I2;
    }
 
    public static void ExtractData(Model mdl, List<Vector3> vtcs, List<TriangleVertexIndices> idcs, bool includeNoncoll)
    {
      Matrix m = Matrix.Identity;
      foreach (ModelMesh mm in mdl.Meshes)
      {
        m = GetAbsoluteTransform(mm.ParentBone);
        ExtractModelMeshData(mm, ref m, vtcs, idcs, "Collision Model", includeNoncoll);
      }
    }
 
    public static Matrix GetAbsoluteTransform(ModelBone bone)
    {
      if (bone == null)
        return Matrix.Identity;
      return bone.Transform * GetAbsoluteTransform(bone.Parent);
    }
 
    public static void ExtractModelMeshData(ModelMesh mm, ref Matrix xform,
        List<Vector3> vertices, List<TriangleVertexIndices> indices, string name, bool includeNoncoll)
    {
      foreach (ModelMeshPart mmp in mm.MeshParts)
      {
 
        if (!includeNoncoll)
        {
          EffectAnnotation annot = mmp.Effect.CurrentTechnique.Annotations["collide"];
          if (annot != null && annot.GetValueBoolean() == false)
          {
            Console.WriteLine("Ignoring model mesh part {0}:{1} because it's set to not collide.",
                name, mm.Name);
            continue;
          }
        }
        ExtractModelMeshPartData(mm, mmp, ref xform, vertices, indices, name);
      }
    }
 
    public static void ExtractModelMeshPartData(ModelMesh mm, ModelMeshPart mmp, ref Matrix xform,
        List<Vector3> vertices, List<TriangleVertexIndices> indices, string name)
    {
      int offset = vertices.Count;
      Vector3[] a = new Vector3[mmp.NumVertices];
      mm.VertexBuffer.GetData<Vector3>(mmp.StreamOffset + mmp.BaseVertex * mmp.VertexStride,
          a, 0, mmp.NumVertices, mmp.VertexStride);
      for (int i = 0; i != a.Length; ++i)
        Vector3.Transform(ref a[i], ref xform, out a[i]);
      vertices.AddRange(a);
 
      if (mm.IndexBuffer.IndexElementSize != IndexElementSize.SixteenBits)
        throw new Exception(
            String.Format("Model {0} uses 32-bit indices, which are not supported.",
                          name));
      short[] s = new short[mmp.PrimitiveCount * 3];
      mm.IndexBuffer.GetData<short>(mmp.StartIndex * 2, s, 0, mmp.PrimitiveCount * 3);
      JigLibX.Geometry.TriangleVertexIndices[] tvi = new JigLibX.Geometry.TriangleVertexIndices[mmp.PrimitiveCount];
      for (int i = 0; i != tvi.Length; ++i)
      {
        tvi[i].I0 = s[i * 3 + 0] + offset;
        tvi[i].I1 = s[i * 3 + 1] + offset;
        tvi[i].I2 = s[i * 3 + 2] + offset;
      }
      indices.AddRange(tvi);
    }