magnum/src/MeshTools/CombineIndexedArrays.h

#ifndef Magnum_MeshTools_CombineIndexedArrays_h
#define Magnum_MeshTools_CombineIndexedArrays_h
/*
    Copyright © 2010, 2011, 2012 Vladimír Vondruš <mosra@centrum.cz>

    This file is part of Magnum.

    Magnum is free software: you can redistribute it and/or modify
    it under the terms of the GNU Lesser General Public License version 3
    only, as published by the Free Software Foundation.

    Magnum 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 version 3 for more details.
*/

/** @file
 * @brief Function Magnum::MeshTools::combineIndexedArrays()
 */

#include <vector>
#include <numeric>
#include <tuple>

#include "Math/Vector.h"
#include "MeshTools/Clean.h"

namespace Magnum { namespace MeshTools {

#ifndef DOXYGEN_GENERATING_OUTPUT
namespace Implementation {

class CombineIndexedArrays {
    public:
        template<class ...T> std::vector<UnsignedInt> operator()(const std::tuple<const std::vector<UnsignedInt>&, std::vector<T>&>&... indexedArrays) {
            /* Compute index count */
            std::size_t _indexCount = indexCount(std::get<0>(indexedArrays)...);

            /* Resulting index array */
            std::vector<UnsignedInt> result;
            result.resize(_indexCount);
            std::iota(result.begin(), result.end(), 0);

            /* All index combinations */
            std::vector<Math::Vector<sizeof...(indexedArrays), UnsignedInt> > indexCombinations(_indexCount);
            writeCombinedIndices(indexCombinations, std::get<0>(indexedArrays)...);

            /* Make the combinations unique */
            MeshTools::clean(result, indexCombinations);

            /* Write combined arrays */
            writeCombinedArrays(indexCombinations, std::get<1>(indexedArrays)...);

            return result;
        }

    private:
        template<class ...T> inline static std::size_t indexCount(const std::vector<UnsignedInt>& first, const std::vector<T>&... next) {
            CORRADE_ASSERT(sizeof...(next) == 0 || indexCount(next...) == first.size(), "MeshTools::combineIndexedArrays(): index arrays don't have the same length, nothing done.", 0);

            return first.size();
        }

        template<std::size_t size, class ...T> static void writeCombinedIndices(std::vector<Math::Vector<size, UnsignedInt>>& output, const std::vector<UnsignedInt>& first, const std::vector<T>&... next) {
            /* Copy the data to output */
            for(std::size_t i = 0; i != output.size(); ++i)
                output[i][size-sizeof...(next)-1] = first[i];

            writeCombinedIndices(output, next...);
        }

        template<std::size_t size, class T, class ...U> static void writeCombinedArrays(const std::vector<Math::Vector<size, UnsignedInt>>& combinedIndices, std::vector<T>& first, std::vector<U>&... next) {
            /* Rewrite output array */
            std::vector<T> output;
            for(std::size_t i = 0; i != combinedIndices.size(); ++i)
                output.push_back(first[combinedIndices[i][size-sizeof...(next)-1]]);
            std::swap(output, first);

            writeCombinedArrays(combinedIndices, next...);
        }

        /* Terminator functions for recursive calls */
        inline static std::size_t indexCount() { return 0; }
        template<std::size_t size> inline static void writeCombinedIndices(std::vector<Math::Vector<size, UnsignedInt>>&) {}
        template<std::size_t size> inline static void writeCombinedArrays(const std::vector<Math::Vector<size, UnsignedInt>>&) {}
};

}
#endif

/**
@brief Combine indexed arrays
@param[in,out] indexedArrays Index and attribute arrays
@return %Array with resulting indices

When you have e.g. vertex, normal and texture array, each indexed with
different indices, you can use this function to combine them to use the same
indices. The function returns array with resulting indices and replaces
original attribute arrays with combined ones.

The index array must be passed as const reference (to avoid copying) and
attribute array as reference, so it can be replaced with combined data. To
avoid explicit verbose specification of tuple type, you can write it with help
of some STL functions like shown below. Also if one index array is shader by
more than one attribute array, just pass the index array more times. Example:
@code
std::vector<UnsignedInt> vertexIndices;
std::vector<Vector3> positions;
std::vector<UnsignedInt> normalTextureIndices;
std::vector<Vector3> normals;
std::vector<Vector2> textureCoordinates;

std::vector<UnsignedInt> indices = MeshTools::combineIndexedArrays(
    std::make_tuple(std::cref(vertexIndices), std::ref(positions)),
    std::make_tuple(std::cref(normalTextureIndices), std::ref(normals)),
    std::make_tuple(std::cref(normalTextureIndices), std::ref(textureCoordinates))
);
@endcode
`positions`, `normals` and `textureCoordinates` will then contain combined
attributes indexed with `indices`.

@attention The function expects that all arrays have the same size.
*/
/* Implementation note: It's done using tuples because it is more clear which
   parameter is index array and which is attribute array, mainly when both are
   of the same type. */
template<class ...T> std::vector<UnsignedInt> combineIndexedArrays(const std::tuple<const std::vector<UnsignedInt>&, std::vector<T>&>&... indexedArrays) {
    return Implementation::CombineIndexedArrays()(indexedArrays...);
}

}}

#endif