Brush.h

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/* Copyright (C) 2021 Wildfire Games.
 * This file is part of 0 A.D.
 *
 * 0 A.D. 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.
 *
 * 0 A.D. 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 0 A.D.  If not, see <http://www.gnu.org/licenses/>.
 */

/*
 * CBrush, a class representing a convex object
 */

#ifndef INCLUDED_BRUSH
#define INCLUDED_BRUSH

#include "maths/Vector3D.h"

#include <vector>

class CBoundingBoxAligned;
class CFrustum;
class CPlane;


/**
 * Class CBrush: Represents a convex object, supports some CSG operations.
 */
class CBrush
{
public:
    CBrush();

    /**
     * CBrush: Construct a brush from a bounds object.
     *
     * @param bounds the CBoundingBoxAligned object to construct the brush from.
     */
    CBrush(const CBoundingBoxAligned& bounds);

    /**
     * IsEmpty: Returns whether the brush is empty.
     *
     * @return @c true if the brush is empty, @c false otherwise
     */
    bool IsEmpty() const { return m_Vertices.size() == 0; }

    /**
     * Bounds: Calculate the axis-aligned bounding box for this brush.
     *
     * @param result the resulting bounding box is stored here
     */
    void Bounds(CBoundingBoxAligned& result) const;

    /**
     * Slice: Cut the object along the given plane, resulting in a smaller (or even empty) brush representing
     * the part of the object that lies in front of the plane (as defined by the positive direction of its
     * normal vector).
     *
     * @param plane the slicing plane
     * @param result the resulting brush is stored here
     */
    void Slice(const CPlane& plane, CBrush& result) const;

    /**
     * Intersect: Intersect the brush with the given frustum.
     *
     * @param frustum the frustum to intersect with
     * @param result the resulting brush is stored here
     */
    void Intersect(const CFrustum& frustum, CBrush& result) const;

    /**
     * Returns vertices in the brush. Intended for testing purposes; you should not need to use
     * this method directly.
     */
    const std::vector<CVector3D>& GetVertices() const;

    /**
     * Writes a vector of the faces in this brush to @p out. Each face is itself a vector, listing the vertex indices
     * that make up the face, starting and ending with the same index. Intended for testing purposes; you should not
     * need to use this method directly.
     */
    void GetFaces(std::vector<std::vector<size_t>>& out) const;

private:
    static const size_t NO_VERTEX = ~0u;

    typedef std::vector<CVector3D> Vertices;
    typedef std::vector<size_t> FaceIndices;

    /// Collection of unique vertices that make up this shape.
    Vertices m_Vertices;

    /**
     * Holds the face definitions of this brush. Each face is a sequence of indices into m_Vertices that starts and ends with
     * the same vertex index, completing a loop through all the vertices that make up the face. This vector holds all the face
     * sequences back-to-back, thus looking something like 'x---xy--------yz--z' in the general case.
     */
    FaceIndices m_Faces;

    struct Helper;
};

#endif // INCLUDED_BRUSH