HierarchicalPathfinder.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/>.
 */

#ifndef INCLUDED_HIERPATHFINDER
#define INCLUDED_HIERPATHFINDER

#include "Pathfinding.h"

#include "ps/CLogger.h"
#include "renderer/TerrainOverlay.h"
#include "Render.h"
#include "graphics/SColor.h"

#include <map>
#include <set>

/**
 * Hierarchical pathfinder.
 *
 * Deals with connectivity (can point A reach point B?).
 *
 * The navcell-grid representation of the map is split into fixed-size chunks.
 * Within a chunk, each maximal set of adjacently-connected passable navcells
 * is defined as a region.
 * Each region is a vertex in the hierarchical pathfinder's graph.
 * When two regions in adjacent chunks are connected by passable navcells,
 * the graph contains an edge between the corresponding two vertexes.
 * By design, there can never be an edge between two regions in the same chunk.
 *
 * Those fixed-size chunks are used to efficiently compute "global regions" by effectively flood-filling.
 * Those can then be used to immediately determine if two reachables points are connected.
 *
 * The main use of this class is to convert an arbitrary PathGoal to a reachable navcell.
 * This happens in MakeGoalReachable.
 *
 */

#ifdef TEST
class TestCmpPathfinder;
class TestHierarchicalPathfinder;
#endif

class HierarchicalOverlay;
class SceneCollector;

class HierarchicalPathfinder
{
#ifdef TEST
    friend class TestCmpPathfinder;
    friend class TestHierarchicalPathfinder;
#endif
public:
    typedef u32 GlobalRegionID;

    struct RegionID
    {
        u8 ci, cj; // chunk ID
        u16 r; // unique-per-chunk local region ID

        RegionID(u8 ci, u8 cj, u16 r) : ci(ci), cj(cj), r(r) { }

        bool operator<(const RegionID& b) const
        {
            // Sort by chunk ID, then by per-chunk region ID
            if (ci < b.ci)
                return true;
            if (b.ci < ci)
                return false;
            if (cj < b.cj)
                return true;
            if (b.cj < cj)
                return false;
            return r < b.r;
        }

        bool operator==(const RegionID& b) const
        {
            return ((ci == b.ci) && (cj == b.cj) && (r == b.r));
        }

        // Returns the distance from the center to the point (i, j)
        inline u32 DistanceTo(u16 i, u16 j) const
        {
            return (ci * CHUNK_SIZE + CHUNK_SIZE/2 - i) * (ci * CHUNK_SIZE + CHUNK_SIZE/2 - i) +
                   (cj * CHUNK_SIZE + CHUNK_SIZE/2 - j) * (cj * CHUNK_SIZE + CHUNK_SIZE/2 - j);
        }

    };

    HierarchicalPathfinder();
    ~HierarchicalPathfinder();

    void SetDebugOverlay(bool enabled, const CSimContext* simContext);

    // Non-pathfinding grids will never be recomputed on calling HierarchicalPathfinder::Update
    void Recompute(Grid<NavcellData>* passabilityGrid,
        const std::map<std::string, pass_class_t>& nonPathfindingPassClassMasks,
        const std::map<std::string, pass_class_t>& pathfindingPassClassMasks);

    void Update(Grid<NavcellData>* grid, const Grid<u8>& dirtinessGrid);

    RegionID Get(u16 i, u16 j, pass_class_t passClass) const;

    GlobalRegionID GetGlobalRegion(u16 i, u16 j, pass_class_t passClass) const;
    GlobalRegionID GetGlobalRegion(RegionID region, pass_class_t passClass) const;

    /**
     * Updates @p goal so that it's guaranteed to be reachable from the navcell
     * @p i0, @p j0 (which is assumed to be on a passable navcell).
     *
     * If the goal is not reachable, it is replaced with a point goal nearest to
     * the goal center.
     *
     * In the case of a non-point reachable goal, it is replaced with a point goal
     * at the reachable navcell of the goal which is nearest to the starting navcell.
     *
     * @returns true if the goal was reachable, false otherwise.
     */
    bool MakeGoalReachable(u16 i0, u16 j0, PathGoal& goal, pass_class_t passClass) const;

    /**
     * @return true if the goal is reachable from navcell i0, j0.
     * (similar to MakeGoalReachable but only checking for reachability).
     */
    bool IsGoalReachable(u16 i0, u16 j0, const PathGoal& goal, pass_class_t passClass) const;

    /**
     * Updates @p i, @p j (which is assumed to be an impassable navcell)
     * to the nearest passable navcell.
     */
    void FindNearestPassableNavcell(u16& i, u16& j, pass_class_t passClass) const;

    /**
     * Generates the connectivity grid associated with the given pass_class
     */
    Grid<u16> GetConnectivityGrid(pass_class_t passClass) const;

    pass_class_t GetPassabilityClass(const std::string& name) const
    {
        auto it = m_PassClassMasks.find(name);
        if (it != m_PassClassMasks.end())
            return it->second;

        LOGERROR("Invalid passability class name '%s'", name.c_str());
        return 0;
    }

    void RenderSubmit(SceneCollector& collector);

private:
    static const u8 CHUNK_SIZE = 96; // number of navcells per side
                                     // TODO: figure out best number. Probably 64 < n < 128

    struct Chunk
    {
        u8 m_ChunkI, m_ChunkJ; // chunk ID
        std::vector<u16> m_RegionsID; // IDs of local regions, 0 (impassable) excluded
        u16 m_Regions[CHUNK_SIZE][CHUNK_SIZE]; // local region ID per navcell

        cassert(CHUNK_SIZE*CHUNK_SIZE/2 < 65536); // otherwise we could overflow m_RegionsID with a checkerboard pattern

        void InitRegions(int ci, int cj, Grid<NavcellData>* grid, pass_class_t passClass);

        RegionID Get(int i, int j) const;

        void RegionCenter(u16 r, int& i, int& j) const;

        void RegionNavcellNearest(u16 r, int iGoal, int jGoal, int& iBest, int& jBest, u32& dist2Best) const;

        bool RegionNearestNavcellInGoal(u16 r, u16 i0, u16 j0, const PathGoal& goal, u16& iOut, u16& jOut, u32& dist2Best) const;

#ifdef TEST
        bool operator==(const Chunk& b) const
        {
            return (m_ChunkI == b.m_ChunkI && m_ChunkJ == b.m_ChunkJ && m_RegionsID.size() == b.m_RegionsID.size() && memcmp(&m_Regions, &b.m_Regions, sizeof(u16) * CHUNK_SIZE * CHUNK_SIZE) == 0);
        }
#endif
    };

    const Chunk& GetChunk(u8 ci, u8 cj, pass_class_t passClass) const
    {
        return m_Chunks.at(passClass).at(cj * m_ChunksW + ci);
    }

    typedef std::map<RegionID, std::set<RegionID> > EdgesMap;

    void ComputeNeighbors(EdgesMap& edges, Chunk& a, Chunk& b, bool transpose, bool opposite) const;
    void RecomputeAllEdges(pass_class_t passClass, EdgesMap& edges);
    void UpdateEdges(u8 ci, u8 cj, pass_class_t passClass, EdgesMap& edges);

    void UpdateGlobalRegions(const std::map<pass_class_t, std::vector<RegionID> >& needNewGlobalRegionMap);

    /**
     * Returns all reachable regions, optionally ordered in a specific manner.
     */
    template<typename Ordering>
    void FindReachableRegions(RegionID from, std::set<RegionID, Ordering>& reachable, pass_class_t passClass) const
    {
        // Flood-fill the region graph, starting at 'from',
        // collecting all the regions that are reachable via edges
        reachable.insert(from);

        const EdgesMap& edgeMap = m_Edges.at(passClass);
        if (edgeMap.find(from) == edgeMap.end())
            return;

        std::vector<RegionID> open;
        open.reserve(64);
        open.push_back(from);

        while (!open.empty())
        {
            RegionID curr = open.back();
            open.pop_back();

            for (const RegionID& region : edgeMap.at(curr))
                // Add to the reachable set; if this is the first time we added
                // it then also add it to the open list
                if (reachable.insert(region).second)
                    open.push_back(region);
        }
    }

    struct SortByCenterToPoint
    {
        SortByCenterToPoint(u16 i, u16 j): gi(i), gj(j) {};
        bool operator()(const HierarchicalPathfinder::RegionID& a, const HierarchicalPathfinder::RegionID& b) const
        {
            if (a.DistanceTo(gi, gj) < b.DistanceTo(gi, gj))
                return true;
            if (a.DistanceTo(gi, gj) > b.DistanceTo(gi, gj))
                return false;
            return a.r < b.r;
        }
        u16 gi, gj;
    };

    void FindNearestNavcellInRegions(const std::set<RegionID, SortByCenterToPoint>& regions,
                                     u16& iGoal, u16& jGoal, pass_class_t passClass) const;

    struct InterestingRegion {
        RegionID region;
        u16 bestI;
        u16 bestJ;
    };

    struct SortByBestToPoint
    {
        SortByBestToPoint(u16 i, u16 j): gi(i), gj(j) {};
        bool operator()(const InterestingRegion& a, const InterestingRegion& b) const
        {
            if ((a.bestI - gi) * (a.bestI - gi) + (a.bestJ - gj) * (a.bestJ - gj) < (b.bestI - gi) * (b.bestI - gi) + (b.bestJ - gj) * (b.bestJ - gj))
                return true;
            if ((a.bestI - gi) * (a.bestI - gi) + (a.bestJ - gj) * (a.bestJ - gj) > (b.bestI - gi) * (b.bestI - gi) + (b.bestJ - gj) * (b.bestJ - gj))
                return false;
            return a.region.r < b.region.r;
        }
        u16 gi, gj;
    };

    // Returns the region along with the best cell for optimisation.
    void FindGoalRegionsAndBestNavcells(u16 i0, u16 j0, u16 gi, u16 gj, const PathGoal& goal, std::set<InterestingRegion, SortByBestToPoint>& regions, pass_class_t passClass) const;

    void FillRegionOnGrid(const RegionID& region, pass_class_t passClass, u16 value, Grid<u16>& grid) const;

    u16 m_W, m_H;
    u8 m_ChunksW, m_ChunksH;
    std::map<pass_class_t, std::vector<Chunk> > m_Chunks;

    std::map<pass_class_t, EdgesMap> m_Edges;

    std::map<pass_class_t, std::map<RegionID, GlobalRegionID> > m_GlobalRegions;
    GlobalRegionID m_NextGlobalRegionID;

    // Passability classes for which grids will be updated when calling Update
    std::map<std::string, pass_class_t> m_PassClassMasks;

    void AddDebugEdges(pass_class_t passClass);
    HierarchicalOverlay* m_DebugOverlay;
    const CSimContext* m_SimContext; // Used for drawing the debug lines

public:
    std::vector<SOverlayLine> m_DebugOverlayLines;
};

class HierarchicalOverlay : public TerrainTextureOverlay
{
public:
    HierarchicalPathfinder& m_PathfinderHier;

    HierarchicalOverlay(HierarchicalPathfinder& pathfinderHier) :
        TerrainTextureOverlay(Pathfinding::NAVCELLS_PER_TERRAIN_TILE), m_PathfinderHier(pathfinderHier)
    {
    }

    virtual void BuildTextureRGBA(u8* data, size_t w, size_t h)
    {
        ENSURE(h <= std::numeric_limits<u16>::max() && w <= std::numeric_limits<u16>::max());
        u16 height = static_cast<u16>(h);
        u16 width = static_cast<u16>(w);
        pass_class_t passClass = m_PathfinderHier.GetPassabilityClass("default");

        for (u16 j = 0; j < height; ++j)
        {
            for (u16 i = 0; i < width; ++i)
            {
                SColor4ub color;

                HierarchicalPathfinder::RegionID rid = m_PathfinderHier.Get(i, j, passClass);
                if (rid.r == 0)
                    color = SColor4ub(0, 0, 0, 0);
                else if (rid.r == 0xFFFF)
                    color = SColor4ub(255, 0, 255, 255);
                else
                    color = GetColor(rid.r + rid.ci*5 + rid.cj*7, 127);

                *data++ = color.R;
                *data++ = color.G;
                *data++ = color.B;
                *data++ = color.A;
            }
        }
    }
};


#endif // INCLUDED_HIERPATHFINDER