- declared FGCondition class and subclasses

- declared FGConditional abstract base class
- declared fgReadCondition global function

src/Main/fg_props.hxx

@@ -691,5 +691,162 @@ fgTie (const string &name, T * obj, int index,
 }
 
 
+
+////////////////////////////////////////////////////////////////////////
+// Conditions.
+////////////////////////////////////////////////////////////////////////
+
+
+/**
+ * An encoded condition.
+ *
+ * This class encodes a single condition of some sort, possibly
+ * connected with properties.
+ *
+ * This class should migrate to somewhere more general.
+ */
+class FGCondition
+{
+public:
+  FGCondition ();
+  virtual ~FGCondition ();
+  virtual bool test () const = 0;
+};
+
+
+/**
+ * Condition for a single property.
+ *
+ * This condition is true only if the property returns a boolean
+ * true value.
+ */
+class FGPropertyCondition : public FGCondition
+{
+public:
+  FGPropertyCondition (const string &propname);
+  virtual ~FGPropertyCondition ();
+  virtual bool test () const { return _node->getBoolValue(); }
+private:
+  const SGPropertyNode * _node;
+};
+
+
+/**
+ * Condition for a 'not' operator.
+ *
+ * This condition is true only if the child condition is false.
+ */
+class FGNotCondition : public FGCondition
+{
+public:
+				// transfer pointer ownership
+  FGNotCondition (FGCondition * condition);
+  virtual ~FGNotCondition ();
+  virtual bool test () const;
+private:
+  FGCondition * _condition;
+};
+
+
+/**
+ * Condition for an 'and' group.
+ *
+ * This condition is true only if all of the conditions
+ * in the group are true.
+ */
+class FGAndCondition : public FGCondition
+{
+public:
+  FGAndCondition ();
+  virtual ~FGAndCondition ();
+  virtual bool test () const;
+				// transfer pointer ownership
+  virtual void addCondition (FGCondition * condition);
+private:
+  vector<FGCondition *> _conditions;
+};
+
+
+/**
+ * Condition for an 'or' group.
+ *
+ * This condition is true if at least one of the conditions in the
+ * group is true.
+ */
+class FGOrCondition : public FGCondition
+{
+public:
+  FGOrCondition ();
+  virtual ~FGOrCondition ();
+  virtual bool test () const;
+				// transfer pointer ownership
+  virtual void addCondition (FGCondition * condition);
+private:
+  vector<FGCondition *> _conditions;
+};
+
+
+/**
+ * Abstract base class for property comparison conditions.
+ */
+class FGComparisonCondition : public FGCondition
+{
+public:
+  enum Type {
+    LESS_THAN,
+    GREATER_THAN,
+    EQUALS
+  };
+  FGComparisonCondition (Type type, bool reverse = false);
+  virtual ~FGComparisonCondition ();
+  virtual bool test () const;
+  virtual void setLeftProperty (const string &propname);
+  virtual void setRightProperty (const string &propname);
+				// will make a local copy
+  virtual void setRightValue (const SGPropertyNode * value);
+private:
+  Type _type;
+  bool _reverse;
+  const SGPropertyNode * _left_property;
+  const SGPropertyNode * _right_property;
+  const SGPropertyNode * _right_value;
+};
+
+
+/**
+ * Base class for a conditional components.
+ *
+ * This class manages the conditions and tests; the component should
+ * invoke the test() method whenever it needs to decide whether to
+ * active itself, draw itself, and so on.
+ */
+class FGConditional
+{
+public:
+  FGConditional ();
+  virtual ~FGConditional ();
+				// transfer pointer ownership
+  virtual void setCondition (FGCondition * condition);
+  virtual const FGCondition * getCondition () const { return _condition; }
+  virtual bool test () const;
+private:
+  FGCondition * _condition;
+};
+
+
+/**
+ * Global function to make a condition out of properties.
+ *
+ * The top-level is always an implicit 'and' group, whatever the
+ * node's name (it should usually be "condition").
+ *
+ * @param node The top-level condition node (usually named "condition").
+ * @return A pointer to a newly-allocated condition; it is the
+ *         responsibility of the caller to delete the condition when
+ *         it is no longer needed.
+ */
+FGCondition * fgReadCondition (const SGPropertyNode * node);
+
+
 #endif // __FG_PROPS_HXX