heightfieldtile.h

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/*
* Copyright 2015 Autodesk, Inc. All rights reserved.
* Use of this software is subject to the terms of the Autodesk license agreement and any attachments or Appendices thereto provided at the time of installation or download,
* or which otherwise accompanies this software in either electronic or hard copy form, or which is signed by you and accepted by Autodesk.
*/

#ifndef Navigation_HeightFieldTile_H
#define Navigation_HeightFieldTile_H

#include "gwnavruntime/math/vec3f.h"
#include "gwnavruntime/math/cardinaldir.h"
#include "gwnavruntime/math/triangle3f.h"
#include "gwnavruntime/navmesh/navmeshtypes.h"

namespace Kaim
{

struct HeightFieldTile
{
    enum TwoDSide
    {
        LeftOfPoint  = 0,
        RightOfPoint = 1,
    };

    HeightFieldTile() : m_entrantDirection(CardinalDir_INVALID) {}

    KY_INLINE KyUInt32 GetSide(const Vec2f& a, const Vec2f& b, const Vec3f& c) const
    {
        return (b.x - a.x)*(c.y - a.y) - (b.y - a.y)*(c.x - a.x) <= 0.f ? RightOfPoint : LeftOfPoint;
    }

    KY_INLINE Triangle3f GetFirstTriangle() const
    {
        Triangle3f tri;
        tri.Set(m_vertices[0], m_vertices[2], m_vertices[3]);
        return tri;
    }
    
    KY_INLINE Triangle3f GetSecondTriangle() const
    {
        Triangle3f tri;
        tri.Set(m_vertices[0], m_vertices[1], m_vertices[2]);
        return tri;
    }

    // This function assumes that m_entrantDirection == CardinalDir_INVALID
    // In other words, we began from within this tile and need to determine the direction in which we exit.
    CardinalDir GetFirstExitDirection(const Vec2f& a, const Vec2f& b) const;

    // This function assumes that m_entrantDirection != CardinalDir_INVALID
    // In other words, we entered the tile from a given direction and know that we cannot "go backwards".
    
    /*
        B       A
        v2--e1--v1  // CCW order in Navigation.
        |       |   // This means that each vertex is numbered such that vN will be the "right" vertex of eN
        e2      e0
        |  /|\  |
        v3--|--v0
            |
            r
    */
    KY_INLINE CardinalDir GetExitDirectionFromEntryDirection(const Vec2f& a, const Vec2f& b) const
    {
        const CardinalDir facingDir = GetOppositeCardinalDir(m_entrantDirection);
        const KyUInt32 rightVertexSide = GetSide(a, b, m_vertices[facingDir]);  // rightVertexSide == 0 if A is to the left of the segment
        const KyUInt32 leftVertexSide = GetSide(a, b, m_vertices[ClampVertexIndex(facingDir + 1)]); // leftVertexSide  == 1 if A to to the right of the segment
        const KyUInt32 exitDirOffset = (rightVertexSide + leftVertexSide * 2 - (rightVertexSide & leftVertexSide)) + 1;

        return ClampVertexIndex(m_entrantDirection + exitDirOffset);
    }

    // Some functions require vertex indices to "wrap" (e.g. 4 => 0 as there is no index '4').
    KY_INLINE KyUInt32 ClampVertexIndex(const KyUInt32 index) const { return index & 3 /* equivalent to % 4 */; }

    CellPos      m_cellPos;
    Vec3f        m_vertices[4];
    CardinalDir  m_entrantDirection;
};

}

#endif //Navigation_HeightField_H