halfmesh_merge_half.hpp

// Description: Merges left and right polygons of a half-edge.

#ifndef PASTELGEOMETRY_HALFMESH_MERGE_HALF_HPP
#define PASTELGEOMETRY_HALFMESH_MERGE_HALF_HPP

#include "pastel/geometry/halfmesh/halfmesh.h"

namespace Pastel
{

    template <
        typename Settings, 
        template <typename> class Customization>
    auto HalfMesh<Settings, Customization>::merge(
        const Half_ConstIterator& half)
    -> Polygon_Iterator
    {
        if (!half.isNormal())
        {
            return Polygon_Iterator();
        }

        Half_Iterator fromTo = cast(half);
        Polygon_Iterator left = fromTo->left();

        Half_Iterator toFrom = fromTo->pair();
        Polygon_Iterator right = toFrom->left();

        if (left.empty() || right.empty() ||
            left == right)
        {
            return Polygon_Iterator();
        }

        Edge_Iterator edge = cast(half->edge());

        // Remove the right polygon.
        removePolygon(right);

        // Detach the left polygon.
        detachPolygon(left);

        if (left->half() == fromTo)
        {
            // The left polygon references a to-be-removed half-edge.

            ASSERT(half->next() != fromTo);

            // Provide the left polygon with the next half-edge.
            left->half_ = fromTo->next();
        }

        // Remove the edge.
        removeEdge(edge);

        // Mark the merged polygon.
        linkPolygon(left->half(), left);

        // Notify the insertion of a new polygon.
        this->onInsertPolygon(left);

        // Return the expanded polygon.
        return left;
    }

    template <
        typename Settings, 
        template <typename> class Customization>
    void HalfMesh<Settings, Customization>::detachPolygon(
        const Polygon_ConstIterator& polygon)
    {
        // Act as if the left polygon were to be removed.
        this->onRemovePolygon(cast(polygon));

        // Detach the left polygon.
        linkPolygon(polygon->half(), Polygon_Iterator());
    }

    template <
        typename Settings, 
        template <typename> class Customization>
    void HalfMesh<Settings, Customization>::linkPolygon(
        const Half_ConstIterator& half,
        const Polygon_ConstIterator& left)
    {
        Half_Iterator h = cast(half);
        do
        {
            h->left_ = cast(left);
            h = h->next();
        }
        while(h != half);

        if (!left.empty())
        {
            cast(left)->half_ = cast(half);
        }
    }

}

#endif