Method aStarPath

src/Battlescape/Pathfinding.cpp:184–236

* Calculates the shortest path using a simple A-Star algorithm. * The unit information and movement type must have already been set. * The path information is set only if a valid path is found. * @param startPosition The position to start from. * @param endPosition The position we want to reach. * @param target Target of the path. * @param sneak Is the unit sneaking? * @param maxTUCost Maxi

 * @return True if a path exists, false otherwise.
 */
bool Pathfinding::aStarPath(const Position &startPosition, const Position &endPosition, BattleUnit *target, bool sneak, int maxTUCost)
{
	// reset every node, so we have to check them all
	for (std::vector<PathfindingNode>::iterator it = _nodes.begin(); it != _nodes.end(); ++it)
		it->reset();

	// start position is the first one in our "open" list
	PathfindingNode *start = getNode(startPosition);
	start->connect(0, 0, 0, endPosition);
	PathfindingOpenSet openList;
	openList.push(start);
	bool missile = (target && maxTUCost == -1);
	// if the open list is empty, we've reached the end
	while(!openList.empty())
	{
		PathfindingNode *currentNode = openList.pop();
		Position const &currentPos = currentNode->getPosition();
		currentNode->setChecked();
		if (currentPos == endPosition) // We found our target.
		{
			_path.clear();
			PathfindingNode *pf = currentNode;
			while (pf->getPrevNode())
			{
				_path.push_back(pf->getPrevDir());
				pf = pf->getPrevNode();
			}
			return true;
		}

		// Try all reachable neighbours.
		for (int direction = 0; direction < 10; direction++)
		{
			Position nextPos;
			int tuCost = getTUCost(currentPos, direction, &nextPos, _unit, target, missile);
			if (tuCost >= 255) // Skip unreachable / blocked
				continue;
			if (sneak && _save->getTile(nextPos)->getVisible()) tuCost *= 2; // avoid being seen
			PathfindingNode *nextNode = getNode(nextPos);
			if (nextNode->isChecked()) // Our algorithm means this node is already at minimum cost.
				continue;
			_totalTUCost = currentNode->getTUCost(missile) + tuCost;
			// If this node is unvisited or has only been visited from inferior paths...
			if ((!nextNode->inOpenSet() || nextNode->getTUCost(missile) > _totalTUCost) && _totalTUCost <= maxTUCost)
			{
				nextNode->connect(_totalTUCost, currentNode, direction, endPosition);
				openList.push(nextNode);
			}
		}
	}
	// Unble to reach the target
	return false;
}

/**
 * Gets the TU cost to move from 1 tile to the other (ONE STEP ONLY).