Get the SoR Robotics Android App on Android Market for FREE. See this forum post for details.

0 Members and 2 Guests are viewing this topic.

do you used a linked list or what?I'm actually writing a paper on this topic right now for my Algorithm Design class.

I talked to someone here at work that knows a little python, he said what you do is create a list of lists and that acts as your 2d array

/*;===================================================================;A* Pathfinder (Version 1.71a) by Patrick Lester. Used by permission.;===================================================================;Last updated 06/16/03 -- Visual C++ version */ //Declare constants const mapWidth = 80, mapHeight = 60, tileSize = 10, numberPeople = 3; int onClosedList = 10; const notfinished = 0, notStarted = 0;// path-related constants const found = 1, nonexistent = 2; const walkable = 0, unwalkable = 1;// walkability array constants //Create needed arrays char walkability [mapWidth][mapHeight]; int openList[mapWidth*mapHeight+2]; //1 dimensional array holding ID# of open list items int whichList[mapWidth+1][mapHeight+1]; //2 dimensional array used to record // whether a cell is on the open list or on the closed list. int openX[mapWidth*mapHeight+2]; //1d array stores the x location of an item on the open list int openY[mapWidth*mapHeight+2]; //1d array stores the y location of an item on the open list int parentX[mapWidth+1][mapHeight+1]; //2d array to store parent of each cell (x) int parentY[mapWidth+1][mapHeight+1]; //2d array to store parent of each cell (y) int Fcost[mapWidth*mapHeight+2]; //1d array to store F cost of a cell on the open list int Gcost[mapWidth+1][mapHeight+1]; //2d array to store G cost for each cell. int Hcost[mapWidth*mapHeight+2]; //1d array to store H cost of a cell on the open list int pathLength[numberPeople+1]; //stores length of the found path for critter int pathLocation[numberPeople+1]; //stores current position along the chosen path for critter int* pathBank [numberPeople+1]; //Path reading variables int pathStatus[numberPeople+1]; int xPath[numberPeople+1]; int yPath[numberPeople+1];//-----------------------------------------------------------------------------// Function Prototypes: where needed//-----------------------------------------------------------------------------void ReadPath(int pathfinderID,int currentX,int currentY, int pixelsPerFrame);int ReadPathX(int pathfinderID,int pathLocation);int ReadPathY(int pathfinderID,int pathLocation);//-----------------------------------------------------------------------------// Name: InitializePathfinder// Desc: Allocates memory for the pathfinder.//-----------------------------------------------------------------------------void InitializePathfinder (void){ for (int x = 0; x < numberPeople+1; x++) pathBank [x] = (int*) malloc(4);}//-----------------------------------------------------------------------------// Name: EndPathfinder// Desc: Frees memory used by the pathfinder.//-----------------------------------------------------------------------------void EndPathfinder (void){ for (int x = 0; x < numberPeople+1; x++) { free (pathBank [x]); }}//-----------------------------------------------------------------------------// Name: FindPath// Desc: Finds a path using A*//-----------------------------------------------------------------------------int FindPath (int pathfinderID,int startingX, int startingY, int targetX, int targetY){ int onOpenList=0, parentXval=0, parentYval=0, a=0, b=0, m=0, u=0, v=0, temp=0, corner=0, numberOfOpenListItems=0, addedGCost=0, tempGcost = 0, path = 0, tempx, pathX, pathY, cellPosition, newOpenListItemID=0;//1. Convert location data (in pixels) to coordinates in the walkability array. int startX = startingX/tileSize; int startY = startingY/tileSize; targetX = targetX/tileSize; targetY = targetY/tileSize;//2.Quick Path Checks: Under the some circumstances no path needs to// be generated ...// If starting location and target are in the same location... if (startX == targetX && startY == targetY && pathLocation[pathfinderID] > 0) return found; if (startX == targetX && startY == targetY && pathLocation[pathfinderID] == 0) return nonexistent;// If target square is unwalkable, return that it's a nonexistent path. if (walkability[targetX][targetY] == unwalkable) goto noPath;//3.Reset some variables that need to be cleared if (onClosedList > 1000000) //reset whichList occasionally { for (int x = 0; x < mapWidth;x++) { for (int y = 0; y < mapHeight;y++) whichList [x][y] = 0; } onClosedList = 10; } onClosedList = onClosedList+2; //changing the values of onOpenList and onClosed list is faster than redimming whichList() array onOpenList = onClosedList-1; pathLength [pathfinderID] = notStarted;//i.e, = 0 pathLocation [pathfinderID] = notStarted;//i.e, = 0 Gcost[startX][startY] = 0; //reset starting square's G value to 0//4.Add the starting location to the open list of squares to be checked. numberOfOpenListItems = 1; openList[1] = 1;//assign it as the top (and currently only) item in the open list, which is maintained as a binary heap (explained below) openX[1] = startX ; openY[1] = startY;//5.Do the following until a path is found or deemed nonexistent. do {//6.If the open list is not empty, take the first cell off of the list.// This is the lowest F cost cell on the open list. if (numberOfOpenListItems != 0) {//7. Pop the first item off the open list. parentXval = openX[openList[1]]; parentYval = openY[openList[1]]; //record cell coordinates of the item whichList[parentXval][parentYval] = onClosedList;//add the item to the closed list// Open List = Binary Heap: Delete this item from the open list, which// is maintained as a binary heap. For more information on binary heaps, see:// http://www.policyalmanac.org/games/binaryHeaps.htm numberOfOpenListItems = numberOfOpenListItems - 1;//reduce number of open list items by 1 // Delete the top item in binary heap and reorder the heap, with the lowest F cost item rising to the top. openList[1] = openList[numberOfOpenListItems+1];//move the last item in the heap up to slot #1 v = 1;// Repeat the following until the new item in slot #1 sinks to its proper spot in the heap. do { u = v; if (2*u+1 <= numberOfOpenListItems) //if both children exist { //Check if the F cost of the parent is greater than each child. //Select the lowest of the two children. if (Fcost[openList[u]] >= Fcost[openList[2*u]]) v = 2*u; if (Fcost[openList[v]] >= Fcost[openList[2*u+1]]) v = 2*u+1; } else { if (2*u <= numberOfOpenListItems) //if only child #1 exists { //Check if the F cost of the parent is greater than child #1 if (Fcost[openList[u]] >= Fcost[openList[2*u]]) v = 2*u; } } if (u != v) //if parent's F is > one of its children, swap them { temp = openList[u]; openList[u] = openList[v]; openList[v] = temp; } else break; //otherwise, exit loop } while (!KeyDown(27));//reorder the binary heap//7.Check the adjacent squares. (Its "children" -- these path children// are similar, conceptually, to the binary heap children mentioned// above, but don't confuse them. They are different. Path children// are portrayed in Demo 1 with grey pointers pointing toward// their parents.) Add these adjacent child squares to the open list// for later consideration if appropriate (see various if statements// below). for (b = parentYval-1; b <= parentYval+1; b++){ for (a = parentXval-1; a <= parentXval+1; a++){// If not off the map (do this first to avoid array out-of-bounds errors) if (a != -1 && b != -1 && a != mapWidth && b != mapHeight){// If not already on the closed list (items on the closed list have// already been considered and can now be ignored). if (whichList[a][b] != onClosedList) { // If not a wall/obstacle square. if (walkability [a][b] != unwalkable) { // Don't cut across corners corner = walkable; if (a == parentXval-1) { if (b == parentYval-1) { if (walkability[parentXval-1][parentYval] == unwalkable || walkability[parentXval][parentYval-1] == unwalkable) \ corner = unwalkable; } else if (b == parentYval+1) { if (walkability[parentXval][parentYval+1] == unwalkable || walkability[parentXval-1][parentYval] == unwalkable) corner = unwalkable; } } else if (a == parentXval+1) { if (b == parentYval-1) { if (walkability[parentXval][parentYval-1] == unwalkable || walkability[parentXval+1][parentYval] == unwalkable) corner = unwalkable; } else if (b == parentYval+1) { if (walkability[parentXval+1][parentYval] == unwalkable || walkability[parentXval][parentYval+1] == unwalkable) corner = unwalkable; } } if (corner == walkable) { // If not already on the open list, add it to the open list. if (whichList[a][b] != onOpenList) { //Create a new open list item in the binary heap. newOpenListItemID = newOpenListItemID + 1; //each new item has a unique ID # m = numberOfOpenListItems+1; openList[m] = newOpenListItemID;//place the new open list item (actually, its ID#) at the bottom of the heap openX[newOpenListItemID] = a; openY[newOpenListItemID] = b;//record the x and y coordinates of the new item //Figure out its G cost if (abs(a-parentXval) == 1 && abs(b-parentYval) == 1) addedGCost = 14;//cost of going to diagonal squares else addedGCost = 10;//cost of going to non-diagonal squares Gcost[a][b] = Gcost[parentXval][parentYval] + addedGCost; //Figure out its H and F costs and parent Hcost[openList[m]] = 10*(abs(a - targetX) + abs(b - targetY)); Fcost[openList[m]] = Gcost[a][b] + Hcost[openList[m]]; parentX[a][b] = parentXval ; parentY[a][b] = parentYval; //Move the new open list item to the proper place in the binary heap. //Starting at the bottom, successively compare to parent items, //swapping as needed until the item finds its place in the heap //or bubbles all the way to the top (if it has the lowest F cost). while (m != 1) //While item hasn't bubbled to the top (m=1) { //Check if child's F cost is < parent's F cost. If so, swap them. if (Fcost[openList[m]] <= Fcost[openList[m/2]]) { temp = openList[m/2]; openList[m/2] = openList[m]; openList[m] = temp; m = m/2; } else break; } numberOfOpenListItems = numberOfOpenListItems+1;//add one to the number of items in the heap //Change whichList to show that the new item is on the open list. whichList[a][b] = onOpenList; }//8.If adjacent cell is already on the open list, check to see if this // path to that cell from the starting location is a better one. // If so, change the parent of the cell and its G and F costs. else //If whichList(a,b) = onOpenList { //Figure out the G cost of this possible new path if (abs(a-parentXval) == 1 && abs(b-parentYval) == 1) addedGCost = 14;//cost of going to diagonal tiles else addedGCost = 10;//cost of going to non-diagonal tiles tempGcost = Gcost[parentXval][parentYval] + addedGCost; //If this path is shorter (G cost is lower) then change //the parent cell, G cost and F cost. if (tempGcost < Gcost[a][b]) //if G cost is less, { parentX[a][b] = parentXval; //change the square's parent parentY[a][b] = parentYval; Gcost[a][b] = tempGcost;//change the G cost //Because changing the G cost also changes the F cost, if //the item is on the open list we need to change the item's //recorded F cost and its position on the open list to make //sure that we maintain a properly ordered open list. for (int x = 1; x <= numberOfOpenListItems; x++) //look for the item in the heap { if (openX[openList[x]] == a && openY[openList[x]] == b) //item found { Fcost[openList[x]] = Gcost[a][b] + Hcost[openList[x]];//change the F cost //See if changing the F score bubbles the item up from it's current location in the heap m = x; while (m != 1) //While item hasn't bubbled to the top (m=1) { //Check if child is < parent. If so, swap them. if (Fcost[openList[m]] < Fcost[openList[m/2]]) { temp = openList[m/2]; openList[m/2] = openList[m]; openList[m] = temp; m = m/2; } else break; } break; //exit for x = loop } //If openX(openList(x)) = a } //For x = 1 To numberOfOpenListItems }//If tempGcost < Gcost(a,b) }//else If whichList(a,b) = onOpenList }//If not cutting a corner }//If not a wall/obstacle square. }//If not already on the closed list }//If not off the map }//for (a = parentXval-1; a <= parentXval+1; a++){ }//for (b = parentYval-1; b <= parentYval+1; b++){ }//if (numberOfOpenListItems != 0)//9.If open list is empty then there is no path. else { path = nonexistent; break; } //If target is added to open list then path has been found. if (whichList[targetX][targetY] == onOpenList) { path = found; break; } } while (1);//Do until path is found or deemed nonexistent//10.Save the path if it exists. if (path == found) {//a.Working backwards from the target to the starting location by checking// each cell's parent, figure out the length of the path. pathX = targetX; pathY = targetY; do { //Look up the parent of the current cell. tempx = parentX[pathX][pathY]; pathY = parentY[pathX][pathY]; pathX = tempx; //Figure out the path length pathLength[pathfinderID] = pathLength[pathfinderID] + 1; } while (pathX != startX || pathY != startY);//b.Resize the data bank to the right size in bytes pathBank[pathfinderID] = (int*) realloc (pathBank[pathfinderID], pathLength[pathfinderID]*8);//c. Now copy the path information over to the databank. Since we are// working backwards from the target to the start location, we copy// the information to the data bank in reverse order. The result is// a properly ordered set of path data, from the first step to the// last. pathX = targetX ; pathY = targetY; cellPosition = pathLength[pathfinderID]*2;//start at the end do { cellPosition = cellPosition - 2;//work backwards 2 integers pathBank[pathfinderID] [cellPosition] = pathX; pathBank[pathfinderID] [cellPosition+1] = pathY;//d.Look up the parent of the current cell. tempx = parentX[pathX][pathY]; pathY = parentY[pathX][pathY]; pathX = tempx;//e.If we have reached the starting square, exit the loop. } while (pathX != startX || pathY != startY); //11.Read the first path step into xPath/yPath arrays ReadPath(pathfinderID,startingX,startingY,1); } return path;//13.If there is no path to the selected target, set the pathfinder's// xPath and yPath equal to its current location and return that the// path is nonexistent.noPath: xPath[pathfinderID] = startingX; yPath[pathfinderID] = startingY; return nonexistent;}//==========================================================//READ PATH DATA: These functions read the path data and convert//it to screen pixel coordinates.void ReadPath(int pathfinderID,int currentX,int currentY, int pixelsPerFrame){/*; Note on PixelsPerFrame: The need for this parameter probably isn't; that obvious, so a little explanation is in order. This; parameter is used to determine if the pathfinder has gotten close; enough to the center of a given path square to warrant looking up; the next step on the path.; ; This is needed because the speed of certain sprites can; make reaching the exact center of a path square impossible.; In Demo #2, the chaser has a velocity of 3 pixels per frame. Our; tile size is 50 pixels, so the center of a tile will be at location; 25, 75, 125, etc. Some of these are not evenly divisible by 3, so; our pathfinder has to know how close is close enough to the center.; It calculates this by seeing if the pathfinder is less than ; pixelsPerFrame # of pixels from the center of the square. ; This could conceivably cause problems if you have a *really* fast; sprite and/or really small tiles, in which case you may need to; adjust the formula a bit. But this should almost never be a problem; for games with standard sized tiles and normal speeds. Our smiley; in Demo #4 moves at a pretty fast clip and it isn't even close; to being a problem.*/ int ID = pathfinderID; //redundant, but makes the following easier to read //If a path has been found for the pathfinder ... if (pathStatus[ID] == found) { //If path finder is just starting a new path or has reached the //center of the current path square (and the end of the path //hasn't been reached), look up the next path square. if (pathLocation[ID] < pathLength[ID]) { //if just starting or if close enough to center of square if (pathLocation[ID] == 0 || (abs(currentX - xPath[ID]) < pixelsPerFrame && abs(currentY - yPath[ID]) < pixelsPerFrame)) pathLocation[ID] = pathLocation[ID] + 1; } //Read the path data. xPath[ID] = ReadPathX(ID,pathLocation[ID]); yPath[ID] = ReadPathY(ID,pathLocation[ID]); //If the center of the last path square on the path has been //reached then reset. if (pathLocation[ID] == pathLength[ID]) { if (abs(currentX - xPath[ID]) < pixelsPerFrame && abs(currentY - yPath[ID]) < pixelsPerFrame) //if close enough to center of square pathStatus[ID] = notStarted; } } //If there is no path for this pathfinder, simply stay in the current //location. else { xPath[ID] = currentX; yPath[ID] = currentY; }}//The following two functions read the raw path data from the pathBank.//You can call these functions directly and skip the readPath function//above if you want. Make sure you know what your current pathLocation//is.//-----------------------------------------------------------------------------// Name: ReadPathX// Desc: Reads the x coordinate of the next path step//-----------------------------------------------------------------------------int ReadPathX(int pathfinderID,int pathLocation){ int x; if (pathLocation <= pathLength[pathfinderID]) { //Read coordinate from bank x = pathBank[pathfinderID] [pathLocation*2-2]; //Adjust the coordinates so they align with the center //of the path square (optional). This assumes that you are using //sprites that are centered -- i.e., with the midHandle command. //Otherwise you will want to adjust this. x = tileSize*x + .5*tileSize; } return x;} //-----------------------------------------------------------------------------// Name: ReadPathY// Desc: Reads the y coordinate of the next path step//-----------------------------------------------------------------------------int ReadPathY(int pathfinderID,int pathLocation){ int y; if (pathLocation <= pathLength[pathfinderID]) { //Read coordinate from bank y = pathBank[pathfinderID] [pathLocation*2-1]; //Adjust the coordinates so they align with the center //of the path square (optional). This assumes that you are using //sprites that are centered -- i.e., with the midHandle command. //Otherwise you will want to adjust this. y = tileSize*y + .5*tileSize; } return y;}