• Create Account

Pathfinding algorithm

Old topic!

Guest, the last post of this topic is over 60 days old and at this point you may not reply in this topic. If you wish to continue this conversation start a new topic.

7 replies to this topic

#1Matthewj234  Members

1069
Like
0Likes
Like

Posted 08 July 2012 - 11:24 AM

So, I have been trying to sort out pathfinding for my game, but it isnt working too well. I have tried A* and it didnt work, so I found this algorithm:

1: Origin is now the current square.
2: select an adjacent square who's still set to 0.
if there's none, goto 5.
3: give the selected square a value of the current square +1.
if the selected square is the target, goto 7
4: push selected square onto a list of unfinished squares. goto 2.
5: shift the first value from the unfinished list, make it the current square.
6: goto 2.
7: Target is now the current square.
9: if selected square's value is current square -1, set it to the current square.
if it's not, goto 8.
10:store the position of the current square relative to the selected square
(Nort, East, South, West etc.)
if it's the origin, goto 12 after that.
11:goto 8.
12:return list of directions

And this is my implementation:

public void findPath(Vec2D startPos, Vec2D endPos) {
Vec2D start = startPos;
Vec2D end = endPos;

boolean finished = false;
boolean step2 = true, step5 = false, step7 = false;

while (!finished) {
Vec2D c = start;

// Step 2
while (step2) {
for (int i = 0; i < 4; i++) {
Vec2D dta = dirs[i];
int nx = c.x + dta.x;
int ny = c.y + dta.y;

if (costs[nx][ny] == 0) {
if (costs[nx][ny] != -1) costs[nx][ny] = costs[c.x][c.y] + 1;
}

runs++;

if (runs >= w * h) return;
if (nx == end.x && ny == end.y) {
// Step 7, result found.
step2 = false;
step7 = true;
break;
}

unfinished.push(new Vec2D(nx, ny));
}

if (step2) {
step5 = true;
}

// Step5
if (step5) {
Vec2D us = unfinished.firstElement();
unfinished.remove(0);
c.x = us.x;
c.y = us.y;
}
}

// Step 7 (End case)
c.x = end.x;
c.y = end.y;
if (step7) {

for (int i = 0; i < 4; i++) {
Vec2D dta = dirs[i];
int nx = c.x + dta.x;
int ny = c.y + dta.y;

if (costs[nx][ny] < costs[c.x][c.y]) {
c.x = nx;
c.y = ny;
break;
}
}

if (c.x == start.x && c.y == start.y) finished = true;
}
}
}
Sadly, it keeps running in a circle, can anyone offer some guidance as to what I have done wrong in the implementation of it, and possibly show me a correct implementation?

#2arkane7  Members

213
Like
1Likes
Like

Posted 09 July 2012 - 02:49 PM

do you want to create a visual path or just want to find a path? I'm not sure on how you could draw the best path but i do know how to solve a maze with a queue (which is a list, but like a line, where who ever got in line first gets out of the line first, i.e. First-In First-Out). Queues (and stacks) have push (add to the end of queue) and pop (remove the front of the queue) operations

here is psuedocode to seeing a maze is solvable

push the start position onto the queue

while (queue is not empty)
{
pop off the front of the queue, this is the current location
if (current location is the end location) '
done

if (NORTH is not marked)
push to the back of the queue and mark the location in some way
repeat for SOUTH, WEST, EAST
}
Always improve, never quit.

#3Matthewj234  Members

1069
Like
0Likes
Like

Posted 09 July 2012 - 03:40 PM

do you want to create a visual path or just want to find a path? I'm not sure on how you could draw the best path but i do know how to solve a maze with a queue (which is a list, but like a line, where who ever got in line first gets out of the line first, i.e. First-In First-Out). Queues (and stacks) have push (add to the end of queue) and pop (remove the front of the queue) operations

here is psuedocode to seeing a maze is solvable

push the start position onto the queue

while (queue is not empty)
{
pop off the front of the queue, this is the current location
if (current location is the end location) '
done

if (NORTH is not marked)
push to the back of the queue and mark the location in some way
repeat for SOUTH, WEST, EAST
}

#4Waterlimon  Members

4373
Like
-1Likes
Like

Posted 09 July 2012 - 04:53 PM

Your algorithm looks like it IS A* to me...

o3o

#5BeerNutts  Members

4288
Like
1Likes
Like

Posted 09 July 2012 - 09:38 PM

So, I have been trying to sort out pathfinding for my game, but it isnt working too well. I have tried A* and it didnt work, so I found this algorithm:

Well, it isn't A* that doesn't work, it was your algorithm. What was your problem with A*? I assume you saw this link?
My Gamedev Journal: 2D Game Making, the Easy Way

---(Old Blog, still has good info): 2dGameMaking
-----
"No one ever posts on that message board; it's too crowded." - Yoga Berra (sorta)

#6Matthewj234  Members

1069
Like
1Likes
Like

Posted 10 July 2012 - 12:14 AM

So, I have been trying to sort out pathfinding for my game, but it isnt working too well. I have tried A* and it didnt work, so I found this algorithm:

Well, it isn't A* that doesn't work, it was your algorithm. What was your problem with A*? I assume you saw this link?

Indeed I have thank you. And yes, it was my implementation that didnt work.

#7Nickie  Members

322
Like
1Likes
Like

Posted 10 July 2012 - 02:33 AM

Hello,
My teacher( we're studing programming in the engineering school ) said its really hard to find a way without recursion so I wrote this in C when I was 9th grade; I hope it will help you, its console app:
1. You enter your starting and ending position; X >= 0, X <= 24, Y >=0, Y < 25. Yeah I know its fixed but I was too lazy that day xD
2. FIll in the closed boxes; Places where you can't use to reach the final destination
3. It will print you a 25x25 grid where 5 is your start position, 6 is your destination, 1 is the generated way, 2 are the "locked" boxes, and 0 is the free space where you could walk but u actually didn't

Please don't jungle me for not using const and references ;/

[source lang="cpp"]#include <stdio.h>#include <math.h>typedef struct _COORD{ int x, y;}COORD;typedef struct _BOX{int info, list;float g, h;COORD parent;}BOX;COORD bestNode();void CheckNeighbours(COORD cp);float magnitute(COORD a, COORD b);//global varsBOX grid[25][25]; // main mazeCOORD ep; // end postion. ( where u must reach )void printmaze(int clear){ //clear flag -> if 1 then it will clear the grid and set it to 0 //else -> jsut print its current state int i, z; for(i = 0; i < 25; i++) { for(z = 0; z < 25; z++) { if(clear == 1) { grid[i][z].info = 0; } printf("%i", grid[i][z].info); } printf("\n"); } printf("\n");}int main(){ COORD cp, sp; int e; COORD ctemp; e = 0; printf("Start point. X: / 0-24 / "); scanf("%i", &sp.y); printf("Start point. Y: / 0-24 / "); scanf("%i", &sp.x); printf("End point. X: / 0-24 / "); scanf("%i", &ep.y); printf("End point. Y: / 0-24 / "); scanf("%i", &ep.x); printmaze(1); //add closed printf("Add a closed block? Yes = 1, No = everything else: "); scanf("%i", &e); while(e == 1) { printf("Closed Block. X: / 0-24 / "); scanf("%i", &cp.y); printf("Closed Block. Y: / 0-24 / "); scanf("%i", &cp.x); grid[cp.x][cp.y].list = 2; grid[cp.x][cp.y].info = 2; // with 2 I've marked the closed postions where u can't go printf("Add a closed block? Yes = 1, No = everything else: "); scanf("%i", &e); } grid[sp.x][sp.y].info = 5; // start point on the grid grid[ep.x][ep.y].info = 6; // end point on the grid printf("\n"); // find best way cp.x = sp.x; cp.y = sp.y; //add to open list; grid[cp.x][cp.y].list = 1; grid[cp.x][cp.y].g = 0; grid[cp.x][cp.y].h = magnitute(cp, ep); while(!(cp.x == ep.x && cp.y == ep.y)) // while we have not reached the target {// current postion.x == end postion.x ... //check best node from open list; cp = bestNode(); printf("checking %i-%i \n", cp.x, cp.y); //check out neighbours; if(cp.x == -25000 || cp.y == -25000) // my grid is fix sized from 0-24 so I use -25000 as a flag { printf("There is no way."); cp.x = ep.x; cp.y = ep.y; }else{ CheckNeighbours(cp); grid[cp.x][cp.y].list = 2; // closed list } } while(!(cp.x == sp.x && cp.y == sp.y)) { cp = grid[cp.x][cp.y].parent; grid[cp.x][cp.y].info = 1; if(cp.x == sp.x && cp.y == sp.y) grid[cp.x][cp.y].info = 5; } printf("\n"); printmaze(2); printf("End. \n"); scanf("%i", &e); return 0;}void CheckNeighbours(COORD cp){ int i, z; COORD ctemp; for(i = -1; i < 2; i++) { for(z = -1; z < 2; z++) { //check if alive; if(cp.x + i >= 0 && cp.x + i < 25 && cp.y + z >= 0 && cp.y + z < 25) { if(!(i == 0 && z == 0)) { if(grid[cp.x + i][cp.y + z].list != 1 && grid[cp.x + i][cp.y + z].list != 2) { //if open list or closed grid[cp.x + i][cp.y + z].list = 1; grid[cp.x + i][cp.y + z].parent.x = cp.x; grid[cp.x + i][cp.y + z].parent.y = cp.y; //record h value ctemp.x = cp.x + i; ctemp.y = cp.y + z; grid[cp.x + i][cp.y + z].h = magnitute(ctemp, ep); grid[cp.x + i][cp.y + z].g = magnitute(ctemp, cp) + grid[cp.x][cp.y].g; printf("new neighbour: %i - %i \n", cp.x + i, cp.y + z); }else if(grid[cp.x + i][cp.y + z].list == 1) { ctemp.x = cp.x + i; ctemp.y = cp.y + z; if( grid[cp.x + i][cp.y + z].g > grid[cp.x][cp.y].g + magnitute(cp, ctemp)) { grid[cp.x + i][cp.y + z].parent = cp; grid[cp.x + i][cp.y + z].g = magnitute(ctemp, cp) + grid[cp.x][cp.y].g; } } } // end if mid } // end if alive } // end for z } return;}COORD bestNode(){ int i, z; int bestf = -25000; int a = 0; COORD bestNode; for(i = 0; i < 25; i++) { for(z = 0; z < 25; z++) { if(grid[i][z].list == 1) { if(a == 0) { a = 1; bestf = grid[i][z].g + grid[i][z].h; bestNode.x = i; bestNode.y = z; } else { if(bestf > grid[i][z].g + grid[i][z].h) { bestf = grid[i][z].g + grid[i][z].h; bestNode.x = i; bestNode.y = z; } } } } } if(a == 0) { bestNode.x = -25000; bestNode.y = -25000; } return bestNode;}float magnitute(COORD a, COORD b){ COORD toret; float ab; if(a.x > b.x) { toret.x = a.x - b.x; }else { toret.x = b.x - a.x; } if(a.y > b.y) { toret.y = a.y - b.y; }else { toret.y = b.y - a.y; } ab = toret.x * toret.x + toret.y * toret.y; ab = sqrt(ab); return ab;}[/source]

#8Matthewj234  Members

1069
Like
0Likes
Like

Posted 11 July 2012 - 03:57 AM

Hello,
My teacher( we're studing programming in the engineering school ) said its really hard to find a way without recursion so I wrote this in C when I was 9th grade; I hope it will help you, its console app:
1. You enter your starting and ending position; X >= 0, X <= 24, Y >=0, Y < 25. Yeah I know its fixed but I was too lazy that day xD
2. FIll in the closed boxes; Places where you can't use to reach the final destination
3. It will print you a 25x25 grid where 5 is your start position, 6 is your destination, 1 is the generated way, 2 are the "locked" boxes, and 0 is the free space where you could walk but u actually didn't

Please don't jungle me for not using const and references ;/

[source lang="cpp"]#include <stdio.h>#include <math.h>typedef struct _COORD{ int x, y;}COORD;typedef struct _BOX{int info, list;float g, h;COORD parent;}BOX;COORD bestNode();void CheckNeighbours(COORD cp);float magnitute(COORD a, COORD b);//global varsBOX grid[25][25]; // main mazeCOORD ep; // end postion. ( where u must reach )void printmaze(int clear){ //clear flag -> if 1 then it will clear the grid and set it to 0 //else -> jsut print its current state int i, z; for(i = 0; i < 25; i++) { for(z = 0; z < 25; z++) { if(clear == 1) { grid[i][z].info = 0; } printf("%i", grid[i][z].info); } printf("\n"); } printf("\n");}int main(){ COORD cp, sp; int e; COORD ctemp; e = 0; printf("Start point. X: / 0-24 / "); scanf("%i", &sp.y); printf("Start point. Y: / 0-24 / "); scanf("%i", &sp.x); printf("End point. X: / 0-24 / "); scanf("%i", &ep.y); printf("End point. Y: / 0-24 / "); scanf("%i", &ep.x); printmaze(1); //add closed printf("Add a closed block? Yes = 1, No = everything else: "); scanf("%i", &e); while(e == 1) { printf("Closed Block. X: / 0-24 / "); scanf("%i", &cp.y); printf("Closed Block. Y: / 0-24 / "); scanf("%i", &cp.x); grid[cp.x][cp.y].list = 2; grid[cp.x][cp.y].info = 2; // with 2 I've marked the closed postions where u can't go printf("Add a closed block? Yes = 1, No = everything else: "); scanf("%i", &e); } grid[sp.x][sp.y].info = 5; // start point on the grid grid[ep.x][ep.y].info = 6; // end point on the grid printf("\n"); // find best way cp.x = sp.x; cp.y = sp.y; //add to open list; grid[cp.x][cp.y].list = 1; grid[cp.x][cp.y].g = 0; grid[cp.x][cp.y].h = magnitute(cp, ep); while(!(cp.x == ep.x && cp.y == ep.y)) // while we have not reached the target {// current postion.x == end postion.x ... //check best node from open list; cp = bestNode(); printf("checking %i-%i \n", cp.x, cp.y); //check out neighbours; if(cp.x == -25000 || cp.y == -25000) // my grid is fix sized from 0-24 so I use -25000 as a flag { printf("There is no way."); cp.x = ep.x; cp.y = ep.y; }else{ CheckNeighbours(cp); grid[cp.x][cp.y].list = 2; // closed list } } while(!(cp.x == sp.x && cp.y == sp.y)) { cp = grid[cp.x][cp.y].parent; grid[cp.x][cp.y].info = 1; if(cp.x == sp.x && cp.y == sp.y) grid[cp.x][cp.y].info = 5; } printf("\n"); printmaze(2); printf("End. \n"); scanf("%i", &e); return 0;}void CheckNeighbours(COORD cp){ int i, z; COORD ctemp; for(i = -1; i < 2; i++) { for(z = -1; z < 2; z++) { //check if alive; if(cp.x + i >= 0 && cp.x + i < 25 && cp.y + z >= 0 && cp.y + z < 25) { if(!(i == 0 && z == 0)) { if(grid[cp.x + i][cp.y + z].list != 1 && grid[cp.x + i][cp.y + z].list != 2) { //if open list or closed grid[cp.x + i][cp.y + z].list = 1; grid[cp.x + i][cp.y + z].parent.x = cp.x; grid[cp.x + i][cp.y + z].parent.y = cp.y; //record h value ctemp.x = cp.x + i; ctemp.y = cp.y + z; grid[cp.x + i][cp.y + z].h = magnitute(ctemp, ep); grid[cp.x + i][cp.y + z].g = magnitute(ctemp, cp) + grid[cp.x][cp.y].g; printf("new neighbour: %i - %i \n", cp.x + i, cp.y + z); }else if(grid[cp.x + i][cp.y + z].list == 1) { ctemp.x = cp.x + i; ctemp.y = cp.y + z; if( grid[cp.x + i][cp.y + z].g > grid[cp.x][cp.y].g + magnitute(cp, ctemp)) { grid[cp.x + i][cp.y + z].parent = cp; grid[cp.x + i][cp.y + z].g = magnitute(ctemp, cp) + grid[cp.x][cp.y].g; } } } // end if mid } // end if alive } // end for z } return;}COORD bestNode(){ int i, z; int bestf = -25000; int a = 0; COORD bestNode; for(i = 0; i < 25; i++) { for(z = 0; z < 25; z++) { if(grid[i][z].list == 1) { if(a == 0) { a = 1; bestf = grid[i][z].g + grid[i][z].h; bestNode.x = i; bestNode.y = z; } else { if(bestf > grid[i][z].g + grid[i][z].h) { bestf = grid[i][z].g + grid[i][z].h; bestNode.x = i; bestNode.y = z; } } } } } if(a == 0) { bestNode.x = -25000; bestNode.y = -25000; } return bestNode;}float magnitute(COORD a, COORD b){ COORD toret; float ab; if(a.x > b.x) { toret.x = a.x - b.x; }else { toret.x = b.x - a.x; } if(a.y > b.y) { toret.y = a.y - b.y; }else { toret.y = b.y - a.y; } ab = toret.x * toret.x + toret.y * toret.y; ab = sqrt(ab); return ab;}[/source]

Thanks, this was really helpful, showing different ways of achieving the same thing.

Old topic!

Guest, the last post of this topic is over 60 days old and at this point you may not reply in this topic. If you wish to continue this conversation start a new topic.