TriangleIterator.hpp

/*
 * Stellarium
 * Copyright (C) 2012 Ferdinand Majerech
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License
 * as published by the Free Software Foundation; either version 2
 * of the License, or (at your option) any later version.
 *
 * This program 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 General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Suite 500, Boston, MA  02110-1335, USA.
 */

#ifndef _TRIANGLEITERATOR_HPP_
#define _TRIANGLEITERATOR_HPP_

#include <QVector>

// For PrimitiveType
#include "renderer/StelVertexBuffer.hpp"


template<class V>
class TriangleIterator
{
public:
    TriangleIterator(const QVector<V>& vertices, const PrimitiveType primitiveType)
        : vertices(vertices)
        , primitiveType(primitiveType)
        , currentVertex(0)
    {
        Q_ASSERT_X(vertices.size() != 1 && vertices.size() != 2, Q_FUNC_INFO,
                   "A vertex array containing triangles of any primitive type must not "
                   "have 1 or 2 vertices");
        switch(primitiveType)
        {
            case PrimitiveType_Triangles:
                Q_ASSERT_X(vertices.size() % 3 == 0, Q_FUNC_INFO,
                           "Size of a vertex array of triangles must be divisible by 3");
                currentVertex = 0;
                break;
            case PrimitiveType_TriangleStrip:
                currentVertex = 2;
                break;
            case PrimitiveType_TriangleFan:
                currentVertex = 1;
                break;
            default:
                Q_ASSERT_X(false, Q_FUNC_INFO, "Not a triangle primitive type");
        }
    }

    bool next(V& a, V& b, V& c)
    {
        Q_ASSERT_X(currentVertex > 0, Q_FUNC_INFO, "Current vertex is negative");
        Q_ASSERT_X(currentVertex <= vertices.size(), Q_FUNC_INFO,
                   "Iterating outside the vertex array");
        if(currentVertex == vertices.size()){return false;}

        switch(primitiveType)
        {
            case PrimitiveType_Triangles:
                a = vertices[currentVertex++];
                b = vertices[currentVertex++];
                c = vertices[currentVertex++];
                break;
            case PrimitiveType_TriangleStrip:
                if(currentVertex % 2 == 0)
                {
                    a = vertices[currentVertex - 2];
                    b = vertices[currentVertex - 1];
                }
                else
                {
                    a = vertices[currentVertex - 1];
                    b = vertices[currentVertex - 2];
                }
                c = vertices[currentVertex];
                ++currentVertex;
                break;
            case PrimitiveType_TriangleFan:
                a = vertices[0];
                b = vertices[currentVertex];
                c = vertices[currentVertex + 1];
                ++currentVertex;
                break;
            default:
                Q_ASSERT_X(false, Q_FUNC_INFO, "Not a triangle primitive type");
        }

        return true;
    }

private:
    const QVector<V>& vertices;

    const PrimitiveType primitiveType;

    int currentVertex;
};

#endif // _TRIANGLEITERATOR_HPP_