Adding Mesh Objects
Windows only

by Dale Fugier (Last updated:  Wednesday, December 12, 2018)

Overview

To create an ON_Mesh:

  1. Create the ON_Mesh object. The constructor requires the number of faces and vertices, and whether or not you have vertex normals or texture coordinates.
  2. Fill in the mesh vertex array, ON_Mesh::m_V. You can also use ON_Mesh::SetVertex.
  3. Fill in the mesh faces array, ON_Mesh::m_F. You can also use ON_Mesh::SetTriangle and ON_Mesh::SetQuad.
  4. If you have vertex normals, fill in the normals array, ON_Mesh::m_N. You can also use ON_Mesh::SetVertexNormal.
  5. If you have texture coordinates, fill in the texture coordinate array, ON_Mesh::m_T. You can also use ON_Mesh::SetTextureCoordinate.
  6. If you did not specify vertex normals, have Rhino compute them for you using ON_Mesh::ComputeVertexNormals().
  7. Clean up everything using ON_Mesh::Compact.

You are now ready to add this mesh object to the document. The opennurbs_mesh.h header file is well documented. It’s worth reading through at least once.

Example

CRhinoCommand::result CCommandTest::RunCommand( const CRhinoCommandContext& context )
{
  // Example demonstrates how to create a mesh and add it to Rhino

  // Create a mesh to write.
  // The mesh is a pyramid with 4 triangular sides and a quadranglar
  // base.  The mesh has 5 vertices and 5 faces.  
  // The side faces share normals at their common vertices.  The
  // quadrangular base has normals different from the side normal.
  // Coincident vertices that have distinct normals must be
  // duplicated in the vertex list.
  //
  // The apex will be at (1,1.5,4) with normal (0,0,1).
  // The base corners will be at (0,0,0), (0,2,0), (2,3,0), (0,3,0).

  bool bHasVertexNormals = true; // we will specify vertex normals
  bool bHasTexCoords = false;    // we will not specify texture coordinates
  const int vertex_count = 5+4;  // 4 duplicates for different base normals
  const int face_count = 5;      // 4 triangle sides and a quad base
  ON_Mesh mesh( face_count, vertex_count, bHasVertexNormals, bHasTexCoords );

  // The SetVertex(), SetNormal(), SetTCoord() and SetFace() functions
  // return true if successful and false if input is illegal.  It is
  // a good idea to inspect this returned value.

  // vertex #0: apex location and normal
  mesh.SetVertex( 0, ON_3dPoint(1.0,  1.5,  5.0) );
  mesh.SetVertexNormal( 0, ON_3dVector(0.0,  0.0,  1.0) );

  // vertex #1: SW corner vertex for sides
  mesh.SetVertex( 1, ON_3dPoint(0.0,  0.0,  0.0) );
  mesh.SetVertexNormal( 1, ON_3dVector(-1.0, -1.0,  0.0) ); // set normal will unitize if needed

  // vertex #2: SE corner vertex for sides
  mesh.SetVertex( 2, ON_3dPoint(2.0,  0.0,  0.0) );
  mesh.SetVertexNormal( 2, ON_3dVector(+1.0, -1.0,  0.0) );

  // vertex #3: NE corner vertex for sides
  mesh.SetVertex( 3, ON_3dPoint(2.0,  3.0,  0.0) );
  mesh.SetVertexNormal( 3, ON_3dVector(+1.0, +1.0,  0.0) );

  // vertex #4: NW corner vertex for sides
  mesh.SetVertex( 4, ON_3dPoint(0.0,  3.0,  0.0) );
  mesh.SetVertexNormal( 4, ON_3dVector(-1.0, +1.0,  0.0) );

  // vertex #5: SW corner vertex for base
  mesh.SetVertex( 5, ON_3dPoint(0.0,  0.0,  0.0) ); // == location of v1
  mesh.SetVertexNormal( 5, ON_3dVector(0.0,  0.0, -1.0) );

  // vertex #6: SE corner vertex for base
  mesh.SetVertex( 6, ON_3dPoint(2.0,  0.0,  0.0) ); // == location of v2
  mesh.SetVertexNormal( 6, ON_3dVector(0.0,  0.0, -1.0) );

  // vertex #7: SW corner vertex for base
  mesh.SetVertex( 7, ON_3dPoint(2.0,  3.0,  0.0) ); // == location of v3
  mesh.SetVertexNormal( 7, ON_3dVector(0.0,  0.0, -1.0) );

  // vertex #8: SW corner vertex for base
  mesh.SetVertex( 8, ON_3dPoint(0.0,  3.0,  0.0) ); // == location of v4
  mesh.SetVertexNormal( 8, ON_3dVector(0.0,  0.0, -1.0) );

  // Faces have vertices ordered counter-clockwise

  // South side triangle
  mesh.SetTriangle( 0, 1, 2, 0 );

  // East side triangle
  mesh.SetTriangle( 1, 2, 3, 0 );

  // North side triangle
  mesh.SetTriangle( 2, 3, 4, 0 );

  // West side triangle
  mesh.SetTriangle( 3, 4, 1, 0 );

  // last face is quadrangular base
  mesh.SetQuad( 4, 5, 8, 7, 6 );

  //////////////////////////////////////////////////////////////
  //////////////////////////////////////////////////////////////

  if( mesh.IsValid() )
  {
    // Most applications expect vertex normals.
    // If they are not present, ComputeVertexNormals sets
    // them by averaging face normals.
    if ( !mesh.HasVertexNormals() )
      mesh.ComputeVertexNormals();

    context.m_doc.AddMeshObject( mesh );
    context.m_doc.Redraw();
  }

  return success;
}

Here is another example:

CRhinoCommand::result CCommandTest::RunCommand(const CRhinoCommandContext& context)
{
  int face_count = 6;
  int vertex_count = 12;
  BOOL bVertexNormals = FALSE;
  BOOL bTextureCoordinates = FALSE;

  ON_Mesh mesh( face_count, vertex_count, bVertexNormals, bTextureCoordinates );
  mesh.SetVertex(  0, ON_3fPoint(0.0f, 0.0f, 1.0f) );
  mesh.SetVertex(  1, ON_3fPoint(1.0f, 0.0f, 1.0f) );
  mesh.SetVertex(  2, ON_3fPoint(2.0f, 0.0f, 1.0f) );
  mesh.SetVertex(  3, ON_3fPoint(3.0f, 0.0f, 0.0f) );
  mesh.SetVertex(  4, ON_3fPoint(0.0f, 1.0f, 1.0f) );
  mesh.SetVertex(  5, ON_3fPoint(1.0f, 1.0f, 2.0f) );
  mesh.SetVertex(  6, ON_3fPoint(2.0f, 1.0f, 1.0f) );
  mesh.SetVertex(  7, ON_3fPoint(3.0f, 1.0f, 0.0f) );
  mesh.SetVertex(  8, ON_3fPoint(0.0f, 2.0f, 1.0f) );
  mesh.SetVertex(  9, ON_3fPoint(1.0f, 2.0f, 1.0f) );
  mesh.SetVertex( 10, ON_3fPoint(2.0f, 2.0f, 1.0f) );
  mesh.SetVertex( 11, ON_3fPoint(3.0f, 2.0f, 1.0f) );
  mesh.SetQuad( 0, 0, 1,  5,  4 );
  mesh.SetQuad( 1, 1, 2,  6,  5 );
  mesh.SetQuad( 2, 2, 3,  7,  6 );
  mesh.SetQuad( 3, 4, 5,  9,  8 );
  mesh.SetQuad( 4, 5, 6, 10,  9 );
  mesh.SetQuad( 5, 6, 7, 11, 10 );
  mesh.ComputeVertexNormals();
  mesh.Compact();

  context.m_doc.AddMeshObject( mesh );
  context.m_doc.Redraw();
  return CRhinoCommand::success;
}