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#ifndef INCLUDED_SLIDESHOW_EXPRESSIONNODE_HXX
#define INCLUDED_SLIDESHOW_EXPRESSIONNODE_HXX

#include "animationfunction.hxx"


/* Definition of ExpressionNode interface */

namespace slideshow
{
    namespace internal
    {
        /** Refinement of AnimationFunction

	        This interface is used by the SMIL function parser, to
	        collapse constant values into precalculated, single nodes.
        */
        class ExpressionNode : public AnimationFunction
        {
        public:
            /** Predicate whether this node is constant.
                    
        	    This predicate returns true, if this node is
                neither time- nor ViewInfo dependent. This allows
                for certain obtimizations, i.e. not the full
                expression tree needs be represented by
                ExpressionNodes.

                @returns true, if this node is neither time- nor
                ViewInfo dependent
            */
            virtual bool isConstant() const = 0;
        };

        typedef ::boost::shared_ptr< ExpressionNode > ExpressionNodeSharedPtr;
    }
}

#endif /* INCLUDED_SLIDESHOW_EXPRESSIONNODE_HXX */