The following examples illustrate the basic steps outlined in Section 6.1, “Overview”. Example 6-1 shows the header file for a simple engine, MultFloatVec3f, which multiplies a float value (SoSFFloat SoSFFloat SoSFFloat ) by a vector value (SoSFVec3f SoSFVec3f SoSFVec3f ) and produces an output of type SoSFVec3f SoSFVec3f SoSFVec3f . Example 6-2 shows the source file for this class.
The SoCalculator SoCalculator SoCalculator engine provides a built-in way of doing this type of simple arithmetic. |
Example 6.1. MultFloatVec3f.h
#include <Inventor/engines/SoSubEngine.h> #include <Inventor/fields/SoSFFloat.h> #include <Inventor/fields/SoSFVec3f.h> class MultFloatVec3f : public SoEngine { SO_ENGINE_HEADER(MultFloatVec3f); public: // Input fields: a scalar (float) and a vector SoSFFloat scalar; SoSFVec3f vector; // The output is a vector SoEngineOutput product; // (SoSFVec3f) product // Initializes this class for use in scene graphs. This // should be called after database initialization and before // any instance of this engine is constructed. static void initClass(); static void exitClass(); // Constructor MultFloatVec3f(); private: // Destructor. Since engines are never deleted explicitly, // this can be private. virtual ~MultFloatVec3f(); // Evaluation method virtual void evaluate(); };
Example 6.2. MultFloatVec3f.c++
#include "MultFloatVec3f.h" SO_ENGINE_SOURCE(MultFloatVec3f); // Initializes the MultFloatVec3f class. This is a one-time // thing that is done after database initialization and before // any instance of this class is constructed. void MultFloatVec3f::initClass() { // Initialize type id variables. The arguments to the macro // are: the name of the engine class, the class this is // derived from, and the name registered with the type // of the parent class. SO_ENGINE_INIT_CLASS(MultFloatVec3f, SoEngine, "Engine"); } void MultFloatVec3f::exitClass() { SO_ENGINE_EXIT_CLASS(MultFloatVec3f); } // Constructor MultFloatVec3f::MultFloatVec3f() { // Do standard constructor stuff SO_ENGINE_CONSTRUCTOR(MultFloatVec3f); // Define input fields and their default values SO_ENGINE_ADD_INPUT(scalar, (0.0)); SO_ENGINE_ADD_INPUT(vector, (0.0, 0.0, 0.0)); // Define the output, specifying its type SO_ENGINE_ADD_OUTPUT(product, SoSFVec3f); } // Destructor. Does nothing. MultFloatVec3f::~MultFloatVec3f() { } // This is the evaluation routine. void MultFloatVec3f::evaluate() { // Compute the product of the input fields SbVec3f prod = scalar.getValue() * vector.getValue(); // "Send" the value to the output. In effect, we are setting // the value in all fields to which this output is connected. SO_ENGINE_OUTPUT(product, SoSFVec3f, setValue(prod)); }