5.2. Complex Shapes

Complex shapes, such as triangle strip sets and face sets, require at least a set of coordinates. If the lighting is set to PHONG, complex shapes also require a set of surface normals, as shown in Figure 5.2, “ Nodes Used to Create a Simple Indexed Face Set ”. Coordinates and normals are defined by separate nodes in the scene graph so that this information can be shared by other nodes.

Examples of complex shapes include the following:

Face set, indexed face set
Line set, indexed line set
Triangle strip set, indexed triangle strip set
Point set
Quad mesh
NURBS curve and surface
Figure 5.1. Shape-Node Classes

An SoCoordinate3⁽^C++^|^Java^|^.NET⁾ node sets the current coordinates in the rendering state to the specified points. This node contains one field (point), which is of type SoMFVec3f⁽^C++^|^Java^|^.NET⁾. For example:

C++

SbVec3f 				verts[6];
SoCoordinate3			 *coord = new SoCoordinate3;
// ...Initialize vertices array ...
coord->point.setValues(0, 6, verts);

.NET

SbVec3f[] verts = new SbVec3f[6];
SoCoordinate3	coord = new SoCoordinate3();
// ...Initialize vertices array ...
coord.point.SetValues(0, verts);

Java

SbVec3f[] verts = new SbVec3f[6];
SoCoordinate3	coord = new SoCoordinate3();
// ...Initialize vertices array ...
coord.point.setValues(0, verts);

An SoNormal⁽^C++^|^Java^|^.NET⁾ node sets the current surface normals in the rendering state to the specified vectors. This node contains one field, vector, of type SoMFVec3f⁽^C++^|^Java^|^.NET⁾.


	Tip: Normals can also be generated automatically by Inventor, in which case you do not need an SoNormal⁽^C++^\|^Java^\|^.NET⁾ node. See the section called “Generating Normals Automatically” for further information.

Figure 5.2. Nodes Used to Create a Simple Indexed Face Set

Face Set

An SoFaceSet⁽^C++^|^Java^|^.NET⁾ is a shape node that represents a polygonal object formed by constructing faces out of the current coordinates, current normals, current materials, and current textures. It uses the values within each node in the order they are given. (To use coordinates, normals, and materials in a different order, use the SoIndexedFaceSet⁽^C++^|^Java^|^.NET⁾ node, described in the next section.)

Example 5.1, “ Creating a Face Set ” creates an obelisk using a face set composed of eight faces. The scene graph for this example is shown in Figure 5.3, “ Scene Graph for Face Set Example ”. Ignore the normal binding node for now. This node is explained in Section 5.4, “Binding Nodes”Figure 5.4, “ Face-Set Example”shows the image created by this example.

Figure 5.3. Scene Graph for Face Set Example

Figure 5.4. Face-Set Example

Example 5.1. Creating a Face Set

C++

//  Eight polygons. The first four are triangles 
//  The second four are quadrilaterals for the sides.
static float vertices[28][3] =
{
   { 0, 30, 0}, {-2,27, 2}, { 2,27, 2},            //front tri
   { 0, 30, 0}, {-2,27,-2}, {-2,27, 2},            //left  tri
   { 0, 30, 0}, { 2,27,-2}, {-2,27,-2},            //rear  tri
   { 0, 30, 0}, { 2,27, 2}, { 2,27,-2},            //right tri
   {-2, 27, 2}, {-4,0, 4}, { 4,0, 4}, { 2,27, 2},  //front quad
   {-2, 27,-2}, {-4,0,-4}, {-4,0, 4}, {-2,27, 2},  //left  quad
   { 2, 27,-2}, { 4,0,-4}, {-4,0,-4}, {-2,27,-2},  //rear  quad
   { 2, 27, 2}, { 4,0, 4}, { 4,0,-4}, { 2,27,-2}   //right quad
};

// Number of vertices in each polygon:
static long numvertices[8] = {3, 3, 3, 3, 4, 4, 4, 4};

// Normals for each polygon:
static float norms[8][3] =
{ 
   {0, .555,  .832}, {-.832, .555, 0}, //front, left tris
   {0, .555, -.832}, { .832, .555, 0}, //rear, right tris
   {0, .0739,  .9973}, {-.9972, .0739, 0},//front, left quads
   {0, .0739, -.9973}, { .9972, .0739, 0},//rear, right quads
};

SoSeparator *
makeObeliskFaceSet()
{
   SoSeparator *obelisk = new SoSeparator();
   obelisk->ref();

   // Define the normals used:
   SoNormal *myNormals = new SoNormal;
   myNormals->vector.setValues(0, 8, norms);
   obelisk->addChild(myNormals);
   SoNormalBinding *myNormalBinding = new SoNormalBinding;
   myNormalBinding->value = SoNormalBinding::PER_FACE;
   obelisk->addChild(myNormalBinding);

   // Define material for obelisk
   SoMaterial *myMaterial = new SoMaterial;
   myMaterial->diffuseColor.setValue(.4, .4, .4);
   obelisk->addChild(myMaterial);

   // Define coordinates for vertices
   SoCoordinate3 *myCoords = new SoCoordinate3;
   myCoords->point.setValues(0, 28, vertices);
   obelisk->addChild(myCoords);

   // Define the FaceSet
   SoFaceSet *myFaceSet = new SoFaceSet;
   myFaceSet->numVertices.setValues(0, 8, numvertices);
   obelisk->addChild(myFaceSet);

   obelisk->unrefNoDelete();
   return obelisk;
}

coordIndex (SoMFLong)	contains indices into the coordinates list. These indices connect coordinates to form a set of faces. A value of SO_END_FACE_INDEX (-1) indicates the end of one face and the start of the next face. This field is always used.
materialIndex (SoMFLong)	contains indices into the current material(s) for the materials of the face set. This field is used only when some type of indexed material binding is specified in the SoMaterialBinding⁽^C++^\|^Java^\|^.NET⁾ node. See Section 5.4, “Binding Nodes”.
normalIndex (SoMFLong)	contains indices into the current normals for the vertices of the face set. This field is used only when indexed normal binding (either per vertex or per face) is specified in the SoNormalBinding⁽^C++^\|^Java^\|^.NET⁾ node. See Section 5.4, “Binding Nodes”.
textureCoordIndex (SoMFLong)	contains indices of the texture coordinates that are applied to the shape (see Chapter 7, Textures).


	If we forget the previous four lines, we will get two coplanar sufaces.


	Tip: Triangle strip sets and quad meshes are generally faster to render than face sets.