i'm making a simple iPhone game using cocos2d-iphone. I have an array of fiends, the "fiendSet" which has to navigate around a field full of obstacles. I spent the last three nights trying to get my A* pathfinding to work. I found the actual A* implementation here on stackoverflow and it works brilliantly. However, once i try to move my fiends around i run into trouble.
Each of my fiends has a CGPoint called motionTarget which contains the x and y values for where the fiend has to go. If only set the positions x and y to absolute values once a second, it works, like so:
-(void) updateFiendPositions:(ccTime)dt {
for (MSWFiend *currFiend in fiendSet) {
currFiend.position = ccp(currFiend.motionTarget.x,currFiend.motionTarget.y);
}
}
However, this doesn't look very nice, the fiends just "jump" 20px each second instead of animating nicely. I only implemented this as a placeholder method to verify the pathfinding. Now i want smooth animation. This is what i did:
-(void) updatePositions:(ccTime) dt {
for (MSWFiend *currFiend in fiendSet) {
if (currFiend.motionTarget.x != -1 && currFiend.motionTarget.y != -1) {
float x,y;
if ((int)floor(currFiend.position.x) < (int)floor(currFiend.motionTarget.x)) {
x = currFiend.position.x+(currFiend.speed*dt);
}
if ((int)floor(currFiend.position.x) > (int)floor(currFiend.motionTarget.x)) {
x = currFiend.position.x-(currFiend.speed*dt);
}
if (abs((int)floor(currFiend.position.x)-(int)floor(currFiend.motionTarget.x)) < 2) {
x = currFiend.motionTarget.x;
}
if ((int)floor(currFiend.position.y) < (int)floor(currFiend.motionTarget.y)) {
y = currFiend.position.y+(currFiend.speed*dt);
}
if ((int)floor(currFiend.position.y) > (int)floor(currFiend.motionTarget.y)) {
y = currFiend.position.y-(currFiend.speed*dt);
}
if (abs((int)floor(currFiend.position.y)-(int)floor(currFiend.motionTarget.y)) < 2) {
y = currFiend.motionTarget.y;
}
currFiend.position = ccp(x,y);
}
}
}
This works great for fiends moving in one direction. As soon as a fiend is supposed to go around a bend, trouble starts. Instead of for example first going up, then right, then down; my fiends will combine the up/right motion into one, they are "cutting corners". I only want my fiends to move either north/south OR east/west for each position update, not both. In other words, i don't want to animate changes to x and y simultaneously. I hope this explanation is clear enough..
I'm pretty sure i have a logic error somewhere.. i just havn't been able to figure it out for the last three sleepless nights after work.. Help!
@Aleph thanks for your suggestion. I found that it was the code which determines when to assign a new motionTarget, that was faulty, not the code i posted to begin with. When you mentioned keeping track of each nodes position, i thought of my motionTarget determination code and found the error after 2-3 hours. I ended up doing it like this:
-(void) updatePositions:(ccTime) dt {
for (MSWFiend *currFiend in fiendSet) {
int fiendGX,fiendGY,targetGX,targetGY,dGX,dGY;
float x,y,snappedX,snappedY;
BOOL snappedIntoPosition = FALSE;
fiendGX = (int)round(100.0f*(currFiend.position.x/20));
fiendGY = (int)round(100.0f*(currFiend.position.y/20));
targetGX = (int)round(100.0f*(currFiend.motionTarget.x/20));
targetGY = (int)round(100.0f*(currFiend.motionTarget.y/20));
snappedX = currFiend.position.x;
snappedY = currFiend.position.y;
dGX = abs(fiendGX-targetGX);
dGY = abs(fiendGY-targetGY);
float snappingThreshold; //1 = snap when 0.1 from motionTarget.
snappingThreshold = currFiend.speed/10;
if (dGX < snappingThreshold && dGY < snappingThreshold) {
snappingThreshold = currFiend.motionTarget.x;
snappingThreshold = currFiend.motionTarget.y;
int newPathStep;
newPathStep = currFiend.pathStep + 1;
currFiend.pathStep = newPathStep;
}
int gX,gY;
gX = [[currFiend.path objectAtIndex:currFiend.pathStep] nodeX];
gY = (tileMap.mapSize.height-[[currFiend.path objectAtIndex:currFiend.pathStep] nodeY])-1;
currFiend.motionTarget = ccp(gX*20,gY*20); //Assign motion target to the next A* node. This is later used by the position updater.
if (currFiend.motionTarget.x != -1 && currFiend.motionTarget.y != -1) {
x = currFiend.motionTarget.x;
y = currFiend.motionTarget.y;
if ((int)floor(currFiend.position.x) < (int)floor(currFiend.motionTarget.x)) {
//Move right
x = snappedX+(currFiend.speed*dt);
if (x > currFiend.motionTarget.x) {
x = currFiend.motionTarget.x;
}
y = snappedY;
}
if ((int)floor(currFiend.position.x) > (int)floor(currFiend.motionTarget.x)) {
//Move left
x = snappedX-(currFiend.speed*dt);
if (x < currFiend.motionTarget.x) {
x = currFiend.motionTarget.x;
}
y = snappedY;
}
if ((int)floor(currFiend.position.y) < (int)floor(currFiend.motionTarget.y)) {
//Move up
y = snappedY+(currFiend.speed*dt);
if (y > currFiend.motionTarget.y) {
y = currFiend.motionTarget.y;
}
x = snappedX;
}
if ((int)floor(currFiend.position.y) > (int)floor(currFiend.motionTarget.y)) {
//Move down
y = snappedY-(currFiend.speed*dt);
if (y < currFiend.motionTarget.y) {
y = currFiend.motionTarget.y;
}
x = snappedX;
}
}
currFiend.position = ccp(x,y);
}
}