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| #define GRID_SIZE 61
#define TS 10
int grid[GRID_SIZE][GRID_SIZE];
// Function Prototypes
void renderGrid();
void setSE();
void makeGrid();
void resetGrid();
enum
{
wallTile,
openTile,
startTile,
endTile,
pathTile,
};
//-------------------------------------- Class Declaration and Instantiation
class Astar
{
public:
// Public Member Variables
enum
{
SEARCHING,
SUCCEEDED,
FAILED,
};
// Node class (class that has x, y, heuristic and parent pointer values
class Node
{
public:
Node()
{
parent = NULL;
g = 0.0;
h = 0.0;
f = 0.0;
}
/*****getDistanceEstimate()*****
*TAKES: int endx: x value of the endNode
* int endy: y value of the endNode
*RETURNS: float: the value of the distance equation squared
*PURPOSE: to calculate and return the distance from this
*node to the endNode
********************************/
float getDistanceEstimate( int endx, int endy )
{
float dx = (float)( (float)x - (float)endx );
float dy = (float)( (float)y - (float)endy );
return ((dx*dx) + (dy*dy));
}
/*****isSameState()*****
*TAKES: Node *rhs: node to check x,y values
*RETURNS: bool: is this the same state?
*PURPOSE: true if the passed node has the same
*x and y values as this node
************************/
bool isSameState( Node *rhs )
{
if( x == rhs -> x && y == rhs -> y )
return true;
else
return false;
}
Node *parent;
float g; // cost of this node + its parents
float h; // heuristic estimate
float f; // g + h
int x, y;
int type;
};
class HeapComparison
{
public:
/*****operator()*****
*TAKES: Node *x: first node for comparison
* Node *y: second node for comparison
*RETURNS: bool: does x have higher f than y?
*PURPOSE: this function is passed to the list sorting
*functions, pop_heap, push_heap, and sort_heap
*this function dictates the order of the list
*the heap functions are an A* optimization
*********************/
bool operator() ( const Node *x, const Node *y ) const
{
return x->f > y->f;
}
};
//---------------------------------------------------------- Member Functions
Astar() { // Constructor
}
~Astar() { // Destructor
clearLists();
}
//Reset function
void clearLists()
{
OPEN.clear();
CLOSED.clear();
SUCCESSORS.clear();
}
/*****getCoords()*****
*TAKES: int xCoord: x coordinate for the desired grid value
* int yCoord: y coordinate for the desired grid value
*RETURNS: int: the tile value of grid[x][y]
*PURPOSE: to return the tile value at coordinates xCoord, yCoord
*Values that are out of bounds (bigger than size of grid)
************************/
int getCoords( int xCoord, int yCoord )
{
if( xCoord < 0 || xCoord >= GRID_SIZE ||
yCoord < 0 || yCoord >= GRID_SIZE )
return wallTile;
return grid[xCoord][yCoord];
}
/*****setStartEnd()*****
*TAKES: int x: x value of startNode
* int y: y value of startNode
* int q: x value of endNode
* int r: y value of endNode
*RETURNS: nothing
*PURPOSE: initializes the startNode and endNode
************************/
void setStartEnd( int x, int y, int q, int r)
{
startNode = new Node;
endNode = new Node;
//Initialize the start and ending nodes
startNode -> x = x;
startNode -> y = y;
startNode -> type = startTile;
endNode -> x = q;
endNode -> y = r;
endNode -> type = endTile;
//Set state of the search algorithm
currentState = SEARCHING;
//Initialize the heuristic variables for the start state
startNode->g = 0;
startNode->h =
startNode->getDistanceEstimate( endNode -> x, endNode ->y );
startNode->f =
startNode->g + startNode->h;
//Starting node has no parents
startNode->parent = NULL;
//Push starting node onto OPEN list
OPEN.push_back( startNode );
// Sort elements in heap
push_heap( OPEN.begin(), OPEN.end(), HeapComparison() );
// Initialise counter for search steps
stepCounter = 0;
}
/*****Search()*****
*TAKES: nothing
*RETURNS: unsigned int: corresponds to a particular state
* SUCCEEDED: found the endNode
* FAILED: didn't find the endNode
* SEARCHING: still searching, keep calling trying
*PURPOSE: A* algorithm. Starts at the lowest f valued node on
*the OPEN list (first iteration is always the startNode) and
*stores it as thisNode. The OPEN list contains every node that
*hasn't been expanded, ie. has not had successors generated for
*it The CLOSED list contains every node that has been expanded,
*Search() then generates all the 0 to 8 successors of thisNode
*and iterates through them. Any successor that is found to meet
*both of the following conditions is placed in the OPEN list
*and it's parent node is stored.
* 1) If this successor is already a node on the OPEN list, and
* the 'f' value of the node on the OPEN list is higher
* than that of the successor. Consequentially, this
* successor was reached faster (from a different direction)
* than it was when it was first put on the OPEN list.
* This successor must be updated on the OPEN list with
* the lower 'f' value.
* 2) If this successor is already a node on the CLOSED list, and
* the 'f' value of the node on the CLOSED list is higher
* than that of the successor. Consequentially, this
* successor was reached faster (from a different direction)
* than it was when it was first put on the CLOSED list.
* Because this successor has already been expanded (it
* is on the CLOSED list) and has a lower 'f' value
* than its similar state on the CLOSED list, this
* successor must be removed from the CLOSED list.
* If this successor meets both criteria, it will be
* placed on the OPEN list and expanded again.
*If this successor is neither on the OPEN nor on the CLOSED lists, it
*will be put on the OPEN list and have it's parent node stored. After
*Search() has stored every worthwhile successor (those that have met
*the two criteria), it will move the successors' parent onto the CLOSED
*list. Search should then be called again, where it will expand the Node
*on the OPEN list with the lowest 'f' value. If a node taken off the OPEN
*list is the endNode, Search() will set the currentState flag to SUCCEEDED
*and terminate the subroutine. If the OPEN list is empty, there are no
*more states to expand, and therefore no way to get to the endNode.
*******************/
unsigned int Search()
{
//Check to see if the search succeeded or failed
if( ( currentState == SUCCEEDED) || ( currentState == FAILED ) )
return currentState;
//The search fails if the OPEN list is empty (no more states to search)
if( OPEN.empty() )
{
currentState = FAILED;
return currentState;
}
// Incremement stepCounter
stepCounter ++;
//Get the node with the lowest f value (list is always sorted in order
//of f values)
Node *thisNode = OPEN.front();
pop_heap( OPEN.begin(), OPEN.end(), HeapComparison() );
OPEN.pop_back();
// Check for the end state
if( thisNode -> type == endTile )
{
//Store the parent of end node so we can move back up the tree
endNode->parent = thisNode->parent;
//Make sure startNode isn't equal to endNode
if( thisNode != startNode )
{
//delete thisNode;
delete thisNode;
}
currentState = SUCCEEDED;
return currentState;
}
//End state not found
else
{
//Generate successors for the node in question
//Start by clearing the successor list of the last "thisNode"
SUCCESSORS.clear();
//Push successors of thisNode into SUCCESSORS list.
Node * newNode;
//Store x and y coords of thisNode's parent so it doesn't go backwards
//Make a case for the startNode (it has no parent)
int parentX = -1;
int parentY = -1;
//Check to see that thisNode has a parent (ie, its not the start node)
if( thisNode -> parent )
{
parentX = thisNode -> parent -> x;
parentY = thisNode -> parent -> y;
}
//Create successor by scanning around thisNode's x,y coords
//Case: Left of thisNode
if( (getCoords( (thisNode -> x)-1, (thisNode -> y) ) != wallTile)
&& !((parentX == (thisNode -> x)-1) && (parentY == (thisNode -> y)))
)
{
newNode = new Node;
newNode -> x = (thisNode -> x)-1;
newNode -> y = thisNode -> y;
newNode -> type = getCoords( (thisNode -> x)-1, (thisNode -> y) );
SUCCESSORS.push_back( newNode );
}
//Case: Right of thisNode
if( (getCoords( (thisNode -> x)+1, (thisNode -> y) ) != wallTile)
&& !((parentX == (thisNode -> x)+1) && (parentY == (thisNode -> y)))
)
{
newNode = new Node;
newNode -> x = (thisNode -> x)+1;
newNode -> y = thisNode -> y;
newNode -> type = getCoords( (thisNode -> x)+1, (thisNode -> y) );
SUCCESSORS.push_back( newNode );
}
//Case: Upper Left of thisNode
if( (getCoords( (thisNode -> x)-1, (thisNode -> y)-1 ) != wallTile)
&& !((parentX == (thisNode -> x)-1) && (parentY == (thisNode -> y)-1))
)
{
newNode = new Node;
newNode -> x = (thisNode -> x)-1;
newNode -> y = (thisNode -> y)-1;
newNode -> type = getCoords( (thisNode -> x)-1, (thisNode -> y)-1 );
SUCCESSORS.push_back( newNode );
}
//Case: Above thisNode
if( (getCoords( (thisNode -> x), (thisNode -> y)-1 ) != wallTile)
&& !((parentX == (thisNode -> x)) && (parentY == (thisNode -> y)-1))
)
{
newNode = new Node;
newNode -> x = thisNode -> x;
newNode -> y = (thisNode -> y)-1;
newNode -> type = getCoords( (thisNode -> x), (thisNode -> y)-1 );
SUCCESSORS.push_back( newNode );
}
//Case: Upper Right of thisNode
if( (getCoords( (thisNode -> x)+1, (thisNode -> y)-1 ) != wallTile)
&& !((parentX == (thisNode -> x)+1)
&& (parentY == (thisNode -> y)-1))
)
{
newNode = new Node;
newNode -> x = (thisNode -> x)+1;
newNode -> y = (thisNode -> y)-1;
newNode -> type =
getCoords( (thisNode -> x)+1, (thisNode -> y)-1 );
SUCCESSORS.push_back( newNode );
}
//Case: Lower Left of thisNode
if( (getCoords( (thisNode -> x)-1, (thisNode -> y)+1 ) != wallTile)
&& !((parentX == (thisNode -> x)-1) && (parentY == (thisNode -> y)+1))
)
{
newNode = new Node;
newNode -> x = (thisNode -> x)-1;
newNode -> y = (thisNode -> y)+1;
newNode -> type = getCoords
( (thisNode -> x)-1, (thisNode -> y)+1 );
SUCCESSORS.push_back( newNode );
}
//Case: Below thisNode
if( (getCoords( (thisNode -> x), (thisNode -> y)+1 ) != wallTile)
&& !((parentX == (thisNode -> x)) && (parentY == (thisNode -> y)+1))
)
{
newNode = new Node;
newNode -> x = thisNode -> x;
newNode -> y = (thisNode -> y)+1;
newNode -> type = getCoords( (thisNode -> x), (thisNode -> y)+1 );
SUCCESSORS.push_back( newNode );
}
//Case: Lower Right of thisNode
if( (getCoords( (thisNode -> x)+1, (thisNode -> y)+1 ) != wallTile)
&& !((parentX == (thisNode -> x)+1)
&& (parentY == (thisNode -> y)+1))
)
{
newNode = new Node;
newNode -> x = (thisNode -> x)+1;
newNode -> y = (thisNode -> y)+1;
newNode -> type = getCoords( (thisNode -> x)+1, (thisNode -> y)+1 );
SUCCESSORS.push_back( newNode );
}
//Iterate through all the successors of thisNode
for( vector< Node * >::iterator successor = SUCCESSORS.begin();
successor != SUCCESSORS.end(); successor ++ )
{
//Store the g value for this successor in a temporary variable
float newg = thisNode->g + 1.0;
//Check to see if this successor is on the open or closed lists
vector< Node * >::iterator openlist;
for( openlist = OPEN.begin(); openlist != OPEN.end(); openlist ++ )
{
if( (*openlist)->isSameState( (*successor) ) )
{
break;
}
}
if( openlist != OPEN.end() )
{
//This successor state is on the OPEN list
//Now check to see which has the lower g value
if( (*openlist) -> g <= newg )
{
delete (*successor);
//the one on OPEN is cheaper than this one
//so trash this successor and continue
continue;
}
}
vector< Node * >::iterator closedlist;
for( closedlist = CLOSED.begin();
closedlist != CLOSED.end(); closedlist ++ )
{
if( (*closedlist) -> isSameState( (*successor) ) )
{
break;
}
}
if( closedlist != CLOSED.end() )
{
//This successor state is on the OPEN list
//Now check to see which has the lower g value
if( (*closedlist) -> g <= newg )
{
//the one on CLOSED is cheaper than this one
//so trash this successor and continue
delete (*successor);
continue;
}
}
//This successor is fewer steps (g's value) away from the start
//Than any occurance on the open or closed list
//save parent so we can back track once (if?) we reach the end
(*successor) -> parent = thisNode;
//Store our temporary g value
(*successor)->g = newg;
//find the distance (squared) from this point to the endnode
(*successor)->h = (*successor) ->
getDistanceEstimate( endNode -> x, endNode -> y );
//Get the final heuristic value f
(*successor)->f = (*successor) -> g + (*successor) -> h;
//Remove successor from CLOSED if it was on it and had lower g
if( closedlist != CLOSED.end() )
{
//remove this successor from CLOSED so we don't
//try to compare it again the next time around
delete (*closedlist);
CLOSED.erase( closedlist );
}
//Update old version of this successor node on OPEN list
if( openlist != OPEN.end() )
{
delete (*openlist);
OPEN.erase( openlist );
//resort the heap
sort_heap( OPEN.begin(), OPEN.end(), HeapComparison() );
}
//Put this successor (with newest values) into the OPEN list
OPEN.push_back( (*successor) );
//Sort the OPEN list
push_heap( OPEN.begin(), OPEN.end(), HeapComparison() );
}
//Push thisNode onto CLOSED, it has been expanded
CLOSED.push_back( thisNode );
}
//End of the else,
//the currentState should only be unsuccessful at this point
return currentState;
}
//Function that moves from the endNode to the startNode
//and changes the path From '.' to 'X'
void writePathToGrid()
{
if( currentState == SUCCEEDED )
{
//Iterate back to the startNode from the endNode
Node *nodeChild = endNode;
Node *nodeParent = endNode->parent;
do
{
if( nodeParent != startNode )
{
nodeParent -> type = pathTile;
grid[nodeParent->x][nodeParent->y] = pathTile;
}
nodeChild = nodeParent;
nodeParent = nodeParent->parent;
}
while( nodeChild != startNode );
}
return;
}
private:
//OPEN list explained in comments before Search()
vector<Node *> OPEN;
//CLOSED list explained in comments before Search()
vector<Node *> CLOSED;
//SUCCESSORS is a list of successive nodes branching out from
//any particular node. It is generated almost every iteration of SEARCH
vector<Node *> SUCCESSORS;
unsigned int currentState;
int stepCounter;
//Start and end state pointers
Node *startNode;
Node *endNode;
} aStarSearch; |
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