VRS - The Virtual Rendering System

version 3.3

visitor.h

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/******************************************************************************
 * VRS - The Virtual Rendering System
 * Copyright (C) 2003 Computer Graphics Systems Group at the 
 * Hasso-Plattner-Institute (HPI), Potsdam, Germany.
 *
 * This  library  is  free  software; you can redistribute it and/or  modify it
 * under the terms of the GNU Lesser General Public  License  as  published  by
 * the  Free  Software  Foundation;  either  version 2.1 of the License, or (at
 * your option) any later version. This library  is  distributed  in  the  hope
 * that  it will be useful, but  WITHOUT ANY WARRANTY; without even the implied
 * warranty of  MERCHANTABILITY or FITNESS FOR A PARTICULAR  PURPOSE.  See  the
 * GNU Lesser General Public License for more details. You should have received
 * a copy of the GNU Lesser+ General Public License along with this library; if
 * not, write to the FreeSoftware Foundation, Inc., 59 Temple Place, Suite 330,
 * Boston, MA, 02111-1307, USA.
 ******************************************************************************/

// $Id: visitor.h 6378 2008-06-02 13:30:09Z Konstantin_Baumann $
// $Date: 2008-06-02 15:30:09 +0200 (Mon, 02 Jun 2008) $
// $Revision: 6378 $
// $State$
// $Author: Konstantin_Baumann $

#ifndef VRS_VISITOR_H
#define VRS_VISITOR_H

#include <vrs/config.h>
#include <cassert>
#include <vector>

namespace VRS {

    // some forward declarations
    class VisitorBase;
    class Visitable;
    template<class T> class Visitor;


    class VRS_CORE_API VisitorBase {
    public:
        enum VisitMode {
            VM_VisitChildren,
            VM_VisitSiblings,
            VM_VisitFinish
        }; // enum VisitMode

        // every base class should have a virtual dtor!
        virtual ~VisitorBase() { }

        virtual bool isStrict() const { return false; }

        const std::vector<Visitable*>& pathToRoot() const { return m_pathToRoot; }

    public:
        // hack to allow access to m_pathToRoot and m_childObjectList for each
        // class which implements the Visitable interface... :-(
        std::vector<Visitable*> m_pathToRoot;
        std::vector<Visitable*> m_childObjectList;
    }; // class VisitorBase

    template<class T>
    class Visitor {
    public:
        virtual ~Visitor() { }

        virtual VisitorBase::VisitMode visit(T* obj, bool pushObj) = 0;
    }; // class Visitor<T>

    class VRS_CORE_API Visitable {
    public:
        virtual ~Visitable() { }

        virtual VisitorBase::VisitMode accept(VisitorBase& visitor) = 0;

    protected:
        virtual void acceptChildren(
            std::vector<Visitable*>& appendChildrenHere
        ) const {
            // default: no child objects present
        }

        bool acceptedImpl(
            VisitorBase& vistor,
            bool pushObj,
            VisitorBase::VisitMode& mode
        ) {
            return true; // absorb the visitor
        }

        VisitorBase::VisitMode acceptHierarchyRecursionImpl(
            VisitorBase& visitor,
            bool pushObj
        ) {
            return VisitorBase::VM_VisitChildren; // absorb the visitor
        }
    };

#define VRS_VISITABLE_IMPL(FATHER)                                                                          \
                                                                                                            \
    typedef FATHER                      VRS_FATHER_VISITABLE;                                               \
    typedef VRS::Visitor<VRS_ThisClass> VRS_VISITOR_OF_THIS;                                                \
                                                                                                            \
    virtual VRS::VisitorBase::VisitMode accept(VRS::VisitorBase& visitor) {                                 \
        assert(typeid(VRS_ThisClass) == typeid(*this));                                                     \
                                                                                                            \
        VRS::VisitorBase::VisitMode mode1 = acceptHierarchyRecursionImpl(visitor, true);                    \
                                                                                                            \
        if(mode1 == VRS::VisitorBase::VM_VisitChildren) {                                                   \
            const size_t currentChildObjectSize = visitor.m_childObjectList.size();                         \
            this->acceptChildren(visitor.m_childObjectList);                                            \
                                                                                                            \
            if(currentChildObjectSize < visitor.m_childObjectList.size()) {                                 \
                visitor.m_pathToRoot.push_back(this);                                                       \
                try {                                                                                       \
                    for(                                                                                    \
                        size_t i = currentChildObjectSize, iEnd = visitor.m_childObjectList.size();         \
                        (i != iEnd) && (mode1 != VRS::VisitorBase::VM_VisitFinish);                         \
                        ++i                                                                                 \
                    ) {                                                                                     \
                        VRS::Visitable* const child = visitor.m_childObjectList[i];                         \
                        if(child) {                                                                         \
                            mode1 = child->accept(visitor);                                                 \
                        }                                                                                   \
                    }                                                                                       \
                } catch(std::exception&) {                                                                  \
                    visitor.m_pathToRoot.pop_back();                                                        \
                    throw;                                                                                  \
                }                                                                                           \
                visitor.m_pathToRoot.pop_back();                                                            \
                visitor.m_childObjectList.resize(currentChildObjectSize);                                   \
            }                                                                                               \
        }                                                                                                   \
                                                                                                            \
        const VRS::VisitorBase::VisitMode mode2 = acceptHierarchyRecursionImpl(visitor, false);             \
        return ((mode1 >= mode2) ? mode1 : mode2);                                                          \
    }                                                                                                       \
                                                                                                            \
    VRS::VisitorBase::VisitMode acceptHierarchyRecursionImpl(VRS::VisitorBase& visitor, bool pushObj) {     \
        VRS::VisitorBase::VisitMode mode = VRS::VisitorBase::VM_VisitChildren;                              \
        if(!acceptedImpl(visitor, pushObj, mode) && !visitor.isStrict()) {                                  \
            return VRS_FATHER_VISITABLE::acceptHierarchyRecursionImpl(visitor, pushObj);                    \
        }                                                                                                   \
        return mode;                                                                                        \
    }                                                                                                       \
                                                                                                            \
    bool acceptedImpl(VRS::VisitorBase& visitor, bool pushObj, VRS::VisitorBase::VisitMode& mode) {         \
        if(VRS_VISITOR_OF_THIS* p = dynamic_cast<VRS_VISITOR_OF_THIS*>(&visitor)) {                         \
            mode = p->visit(this, pushObj);                                                                 \
            return true;                                                                                    \
        }                                                                                                   \
        return false;                                                                                       \
    }

#define VRS_IS_STRICT_VISITOR \
    virtual bool isStrict() const { return true; }

#define VRS_VISITABLE_BASE \
    VRS_VISITABLE_IMPL(VRS::Visitable)

#define VRS_VISITABLE \
    VRS_VISITABLE_IMPL(VRS_BaseClass)

} // namespace VRS

#endif // VRS_VISITOR_H

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