Creating a Simple Engine

The following examples illustrate the basic steps outlined in Overview. Example 6-1 shows the header file for a simple engine, MultFloatVec3f, which multiplies a float value (SoSFFloat) by a vector value (SoSFVec3f) and produces an output of type SoSFVec3f. Example 6-2 shows the source file for this class.

The SoCalculator engine provides a built-in way of doing this type of simple arithmetic.

Example : 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 : 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 ) );
}