aystar.cpp

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/*
 * This file is part of OpenTTD.
 * 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.
 * 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.
 * 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/>.
 */
 
#include "../../stdafx.h"
#include "aystar.h"
 
#include "../../safeguards.h"
 
void AyStar::OpenListAdd(PathNode *parent, const AyStarNode *node, int f, int g)
{
  /* Add a new Node to the OpenList */
  PathNode *new_node = this->nodes.CreateNewNode();
  new_node->Set(parent, node->m_tile, node->m_td, true);
  new_node->m_estimate = f;
  new_node->m_cost = g;
  this->nodes.InsertOpenNode(*new_node);
}
 
void AyStar::CheckTile(AyStarNode *current, PathNode *parent)
{
  /* Check the new node against the ClosedList */
  if (this->nodes.FindClosedNode(*current) != nullptr) return;
 
  /* Calculate the G-value for this node */
  int new_g = this->CalculateG(this, current, parent);
  /* If the value was INVALID_NODE, we don't do anything with this node */
  if (new_g == AYSTAR_INVALID_NODE) return;
 
  /* There should not be given any other error-code.. */
  assert(new_g >= 0);
  /* Add the parent g-value to the new g-value */
  new_g += parent->m_cost;
  if (this->max_path_cost != 0 && new_g > this->max_path_cost) return;
 
  /* Calculate the h-value */
  int new_h = this->CalculateH(this, current, parent);
  /* There should not be given any error-code.. */
  assert(new_h >= 0);
 
  /* The f-value if g + h */
  int new_f = new_g + new_h;
 
  /* Get the pointer to the parent in the ClosedList (the current one is to a copy of the one in the OpenList) */
  PathNode *closedlist_parent = this->nodes.FindClosedNode(parent->m_key);
 
  /* Check if this item is already in the OpenList */
  PathNode *check = this->nodes.FindOpenNode(*current);
  if (check != nullptr) {
    /* Yes, check if this g value is lower.. */
    if (new_g > check->m_cost) return;
    this->nodes.PopOpenNode(check->m_key);
    /* It is lower, so change it to this item */
    check->m_estimate = new_f;
    check->m_cost = new_g;
    check->m_parent = closedlist_parent;
    /* Re-add it in the openlist_queue. */
    this->nodes.InsertOpenNode(*check);
  } else {
    /* A new node, add it to the OpenList */
    this->OpenListAdd(closedlist_parent, current, new_f, new_g);
  }
}
 
int AyStar::Loop()
{
  /* Get the best node from OpenList */
  PathNode *current = this->nodes.PopBestOpenNode();
  /* If empty, drop an error */
  if (current == nullptr) return AYSTAR_EMPTY_OPENLIST;
 
  /* Check for end node and if found, return that code */
  if (this->EndNodeCheck(this, current) == AYSTAR_FOUND_END_NODE && current->m_parent != nullptr) {
    if (this->FoundEndNode != nullptr) {
      this->FoundEndNode(this, current);
    }
    return AYSTAR_FOUND_END_NODE;
  }
 
  /* Add the node to the ClosedList */
  this->nodes.InsertClosedNode(*current);
 
  /* Load the neighbours */
  this->GetNeighbours(this, current);
 
  /* Go through all neighbours */
  for (auto &neighbour : this->neighbours) {
    /* Check and add them to the OpenList if needed */
    this->CheckTile(&neighbour, current);
  }
 
  if (this->max_search_nodes != 0 && this->nodes.ClosedCount() >= this->max_search_nodes) {
    /* We've expanded enough nodes */
    return AYSTAR_LIMIT_REACHED;
  } else {
    /* Return that we are still busy */
    return AYSTAR_STILL_BUSY;
  }
}
 
int AyStar::Main()
{
  int r, i = 0;
  /* Loop through the OpenList
   *  Quit if result is no AYSTAR_STILL_BUSY or is more than loops_per_tick */
  while ((r = this->Loop()) == AYSTAR_STILL_BUSY && (this->loops_per_tick == 0 || ++i < this->loops_per_tick)) { }
#ifdef AYSTAR_DEBUG
  switch (r) {
    case AYSTAR_FOUND_END_NODE: Debug(misc, 0, "[AyStar] Found path!"); break;
    case AYSTAR_EMPTY_OPENLIST: Debug(misc, 0, "[AyStar] OpenList run dry, no path found"); break;
    case AYSTAR_LIMIT_REACHED:  Debug(misc, 0, "[AyStar] Exceeded search_nodes, no path found"); break;
    default: break;
  }
#endif
 
  switch (r) {
    case AYSTAR_FOUND_END_NODE: return AYSTAR_FOUND_END_NODE;
    case AYSTAR_EMPTY_OPENLIST:
    case AYSTAR_LIMIT_REACHED:  return AYSTAR_NO_PATH;
    default:                    return AYSTAR_STILL_BUSY;
  }
}
 
void AyStar::AddStartNode(AyStarNode *start_node, int g)
{
#ifdef AYSTAR_DEBUG
  Debug(misc, 0, "[AyStar] Starting A* Algorithm from node ({}, {}, {})\n",
    TileX(start_node->tile), TileY(start_node->tile), start_node->direction);
#endif
  this->OpenListAdd(nullptr, start_node, 0, g);
}