src/pathfinder/aystar.cpp

   1 /*
   2  * This file is part of OpenTTD.
   3  * OpenTTD 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, version 2.
   4  * OpenTTD 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.
   5  * See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with OpenTTD. If not, see <http://www.gnu.org/licenses/>.
   6  */
   7
   8 /** @file aystar.cpp Implementation of A*.
   9  *
  10  * This file has the core function for %AyStar.
  11  * %AyStar is a fast path finding routine and is used for things like AI path finding and Train path finding.
  12  * For more information about %AyStar (A* Algorithm), you can look at
  13  * <A HREF='http://en.wikipedia.org/wiki/A-star_search_algorithm'>http://en.wikipedia.org/wiki/A-star_search_algorithm</A>.
  14  */
  15
  16 #include "../../stdafx.h"
  17 #include "aystar.h"
  18
  19 #include "../../safeguards.h"
  20
  21 /**
  22  * Adds a node to the open list.
  23  * It makes a copy of node, and puts the pointer of parent in the struct.
  24  */
  25 void AyStar::OpenListAdd(PathNode *parent, const AyStarNode *node, int f, int g)
  26 {
  27         /* Add a new Node to the OpenList */
  28         PathNode *new_node = this->nodes.CreateNewNode();
  29         new_node->Set(parent, node->m_tile, node->m_td, true);
  30         new_node->m_estimate = f;
  31         new_node->m_cost = g;
  32         this->nodes.InsertOpenNode(*new_node);
  33 }
  34
  35 /**
  36  * Checks one tile and calculate its f-value
  37  */
  38 void AyStar::CheckTile(AyStarNode *current, PathNode *parent)
  39 {
  40         /* Check the new node against the ClosedList */
  41         if (this->nodes.FindClosedNode(*current) != nullptr) return;
  42
  43         /* Calculate the G-value for this node */
  44         int new_g = this->CalculateG(this, current, parent);
  45         /* If the value was INVALID_NODE, we don't do anything with this node */
  46         if (new_g == AYSTAR_INVALID_NODE) return;
  47
  48         /* There should not be given any other error-code.. */
  49         assert(new_g >= 0);
  50         /* Add the parent g-value to the new g-value */
  51         new_g += parent->m_cost;
  52         if (this->max_path_cost != 0 && new_g > this->max_path_cost) return;
  53
  54         /* Calculate the h-value */
  55         int new_h = this->CalculateH(this, current, parent);
  56         /* There should not be given any error-code.. */
  57         assert(new_h >= 0);
  58
  59         /* The f-value if g + h */
  60         int new_f = new_g + new_h;
  61
  62         /* Get the pointer to the parent in the ClosedList (the current one is to a copy of the one in the OpenList) */
  63         PathNode *closedlist_parent = this->nodes.FindClosedNode(parent->m_key);
  64
  65         /* Check if this item is already in the OpenList */
  66         PathNode *check = this->nodes.FindOpenNode(*current);
  67         if (check != nullptr) {
  68                 /* Yes, check if this g value is lower.. */
  69                 if (new_g > check->m_cost) return;
  70                 this->nodes.PopOpenNode(check->m_key);
  71                 /* It is lower, so change it to this item */
  72                 check->m_estimate = new_f;
  73                 check->m_cost = new_g;
  74                 check->m_parent = closedlist_parent;
  75                 /* Re-add it in the openlist_queue. */
  76                 this->nodes.InsertOpenNode(*check);
  77         } else {
  78                 /* A new node, add it to the OpenList */
  79                 this->OpenListAdd(closedlist_parent, current, new_f, new_g);
  80         }
  81 }
  82
  83 /**
  84  * This function is the core of %AyStar. It handles one item and checks
  85  * its neighbour items. If they are valid, they are added to be checked too.
  86  * @return Possible values:
  87  *  - #AYSTAR_EMPTY_OPENLIST : indicates all items are tested, and no path has been found.
  88  *  - #AYSTAR_LIMIT_REACHED : Indicates that the max_search_nodes limit has been reached.
  89  *  - #AYSTAR_FOUND_END_NODE : indicates we found the end. Path_found now is true, and in path is the path found.
  90  *  - #AYSTAR_STILL_BUSY : indicates we have done this tile, did not found the path yet, and have items left to try.
  91  */
  92 int AyStar::Loop()
  93 {
  94         /* Get the best node from OpenList */
  95         PathNode *current = this->nodes.PopBestOpenNode();
  96         /* If empty, drop an error */
  97         if (current == nullptr) return AYSTAR_EMPTY_OPENLIST;
  98
  99         /* Check for end node and if found, return that code */
 100         if (this->EndNodeCheck(this, current) == AYSTAR_FOUND_END_NODE && current->m_parent != nullptr) {
 101                 if (this->FoundEndNode != nullptr) {
 102                         this->FoundEndNode(this, current);
 103                 }
 104                 return AYSTAR_FOUND_END_NODE;
 105         }
 106
 107         /* Add the node to the ClosedList */
 108         this->nodes.InsertClosedNode(*current);
 109
 110         /* Load the neighbours */
 111         this->GetNeighbours(this, current);
 112
 113         /* Go through all neighbours */
 114         for (auto &neighbour : this->neighbours) {
 115                 /* Check and add them to the OpenList if needed */
 116                 this->CheckTile(&neighbour, current);
 117         }
 118
 119         if (this->max_search_nodes != 0 && this->nodes.ClosedCount() >= this->max_search_nodes) {
 120                 /* We've expanded enough nodes */
 121                 return AYSTAR_LIMIT_REACHED;
 122         } else {
 123                 /* Return that we are still busy */
 124                 return AYSTAR_STILL_BUSY;
 125         }
 126 }
 127
 128 /**
 129  * This is the function you call to run AyStar.
 130  * @return Possible values:
 131  *  - #AYSTAR_FOUND_END_NODE : indicates we found an end node.
 132  *  - #AYSTAR_NO_PATH : indicates that there was no path found.
 133  *  - #AYSTAR_STILL_BUSY : indicates we have done some checked, that we did not found the path yet, and that we still have items left to try.
 134  * @note When the algorithm is done (when the return value is not #AYSTAR_STILL_BUSY) #Clear() is called automatically.
 135  *       When you stop the algorithm halfway, you should call #Clear() yourself!
 136  */
 137 int AyStar::Main()
 138 {
 139         int r, i = 0;
 140         /* Loop through the OpenList
 141          *  Quit if result is no AYSTAR_STILL_BUSY or is more than loops_per_tick */
 142         while ((r = this->Loop()) == AYSTAR_STILL_BUSY && (this->loops_per_tick == 0 || ++i < this->loops_per_tick)) { }
 143 #ifdef AYSTAR_DEBUG
 144         switch (r) {
 145                 case AYSTAR_FOUND_END_NODE: Debug(misc, 0, "[AyStar] Found path!"); break;
 146                 case AYSTAR_EMPTY_OPENLIST: Debug(misc, 0, "[AyStar] OpenList run dry, no path found"); break;
 147                 case AYSTAR_LIMIT_REACHED:  Debug(misc, 0, "[AyStar] Exceeded search_nodes, no path found"); break;
 148                 default: break;
 149         }
 150 #endif
 151
 152         switch (r) {
 153                 case AYSTAR_FOUND_END_NODE: return AYSTAR_FOUND_END_NODE;
 154                 case AYSTAR_EMPTY_OPENLIST:
 155                 case AYSTAR_LIMIT_REACHED:  return AYSTAR_NO_PATH;
 156                 default:                    return AYSTAR_STILL_BUSY;
 157         }
 158 }
 159
 160 /**
 161  * Adds a node from where to start an algorithm. Multiple nodes can be added
 162  * if wanted. You should make sure that #Clear() is called before adding nodes
 163  * if the #AyStar has been used before (though the normal main loop calls
 164  * #Clear() automatically when the algorithm finishes.
 165  * @param start_node Node to start with.
 166  * @param g the cost for starting with this node.
 167  */
 168 void AyStar::AddStartNode(AyStarNode *start_node, int g)
 169 {
 170 #ifdef AYSTAR_DEBUG
 171         Debug(misc, 0, "[AyStar] Starting A* Algorithm from node ({}, {}, {})\n",
 172                 TileX(start_node->tile), TileY(start_node->tile), start_node->direction);
 173 #endif
 174         this->OpenListAdd(nullptr, start_node, 0, g);
 175 }