# Wall following problems.

Monkey Forums/Monkey Beginners/Wall following problems.
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I spend hours trying to get a feature from a platformer game that I saw on a stream working. It had ai that moved around platforms. I looked up how to do this wall following and did not find a lot of explanations. One psuedo code I found was this. if nothing on the left side turn to the left 90 degrees elseif nothing in fron move forward else turn to the right 90 degrees end if I modified the code multiple times and got it to do some kinds of movement around the map but it never really worked like it should. I hope someone knows this wall following technique and can help me out with it. This is the wall following code. Method update() Local y1:Int=y/tileheight Local x1:Int=x/tilewidth ' these variables are used to see if a tile is left of the ai ' and if a tile is in front of the ai Local wallleft:Bool=True Local infront:Bool = True Local angle2:Int=angle-90 If angle2<0 Then angle=270 Local x2:Float=Cos(angle2)*tilewidth Local y2:Float=Sin(angle2)*tileheight x2/=tilewidth y2/=tileheight ' see if a tile is left of the ai If map[y1+y2][x1+x2] = 0 Then wallleft = False x2=Cos(angle)*tilewidth y2=Sin(angle)*tileheight x2/=tilewidth y2/=tileheight ' see if a tile is infront of te ai If map[y1+y2][x1+x2] = 0 Then infront = False ' this handles the wall following. If wallleft = False' if nothing on the left then turn to the left angle-=90 Elseif infront = False 'if nothing in front then move ahead x+=Cos(angle)*1 y+=Sin(angle)*1 Else ' if nothing is right then turn right angle+=90 End If ' keep the angle inside the 0-360 position If angle<0 Then angle=270 If angle>360 Then angle=90 End Method Here is the complete code that runs. Here's hoping that someone knows what is wrong :) |

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The pseudo-code is misleading/over-simplified. If you take the case where you move forward into a space where you can turn left in a square grid environment and then turn on the spot you will always end up with a gap on your left again (the space you previously moved from). As stands you're just running those checks every frame so you'll end up with the AI making double turns or spinning on the spot. In order for the algorithm to work you need to turn left, then move into the space and then run the decision test again. There are a number of other issues with the code and the way you're converting between pixel space and your level grid but that's the main problem with the wall-following itself. |

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I hoped it was a simple thing I did wrong. I wil need to try to expand the code then. Anyways, it was not really that important for me at this time. I saw it and thought it would be nice if I could make it myself. There was not much I could find with google on the technique. I found no working code yet. One example code on a forum did not work after converting it twice. Maybe I wil get it working in the future. With the pixel space and the map coordinates. If you have a way that works better then I would gladly learn about that if it is not to difficult or involves vectors or so. I also tried doing this with for loops and going in to the direction one pixel at a time until I would of reached another map coordinate. Anyways, Thanks for the help so far. |

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I finally figured out how to get those wall crawling baddies in the game. I went through the steps again and now finally saw how it could work. It did not take long to get working. It goes like this. A crawler has 4 possible directions it can go into. We remember the direction we are going into.(1=up-2=right-3=down-4=left) going to the right means increasing the counter to 2+1 = 3(down) We do this: See if the right side is a free and move there;return of if the forward pos is free and move there;return of if the left pos is free and move there This is the crawler class: Class wallcrawler 'x and y tilepositions(cells) Field x:Float,y:Float 'nx and ny is next tileposition Field nx:Int,ny:Int 'offset for drawing (smooth movement) Field offx:Int,offy:Int ' direction wallcrawler is goint to ' 1 = up, 2 = right, 3 = down, 4 = left Field direction:Int Method New(x:Float,y:Float) Self.x = x Self.y = y Self.nx = x Self.ny = y 'start going right Self.direction = 2 End Method Method update() If x = nx And y = ny Else ' if not on next position then slowly move there If x<nx Then offx+=1 If x>nx Then offx-=1 If y<ny Then offy+=1 If y>ny Then offy-=1 If offx>tilewidth Then x+=1;offx=0 If offx<-tilewidth Then x-=1;offx=0 If offy>tileheight Then y+=1;offy=0 If offy<-tileheight Then y-=1;offy=0 Return End If ' get the next directions Local rightd:Int=direction+1 Local forwardd:Int=direction Local leftd:Int=direction-1 ' b sure to stay in legal movement If rightd > 4 Then rightd = 1 If leftd < 1 Then leftd = 4 ' first see if we can go right If postaken(rightd) = True direction = rightd movepos(rightd) Return End If ' then see if we can go forward If postaken(forwardd) = True direction = forwardd movepos(forwardd) Return End If 'then see if we can go left If postaken(leftd) = True direction = leftd movepos(leftd) Return End If End Method ' get next cell position Method movepos(d:Int) nx = x ny = y Select d Case 1;ny-=1 Case 2;nx+=1 Case 3;ny+=1 Case 4;nx-=1 End Select End Method 'see if the next possible position if a wall Method postaken(d:Int) Select d Case 1;If map[y-1][x] = 0 Then Return True Case 2;If map[y][x+1] = 0 Then Return True Case 3;If map[y+1][x] = 0 Then Return True Case 4;If map[y][x-1] = 0 Then Return True End Select Return False End Method Method draw() SetColor 255,0,0 DrawRect x*tilewidth+offx,y*tileheight+offy,tilewidth,tileheight End Method End Class |