Pacman Ghost Random Moving Pattern...WTF?

[Aziz]

Why does this guy go through walls? (btw, EMPTY is a constant with value 1, the empty spaces in the map

code:

var rChange, cChange : int             loop                 rChange := Rand.Int (-1, 1)                 cChange := Rand.Int (-1, 1)                 exit when (rChange ~= 0 and cChange = 0) or (rChange = 0 and cChange ~= 0)             end loop             if Rand.Real > 0.9 and map (g.r + rChange, g.c + cChange) = EMPTY then                 g.rChange := rChange                 g.cChange := cChange             end if             if map (g.r + rChange, g.c + cChange) = EMPTY then                 g.r += g.rChange                 g.c += g.cChange             end if

[Jorbalax]

It's really hard to determine what the problem is with just that small line of coding. Perhaps you should post a bit more.

Also...

code:

loop                 rChange := Rand.Int (-1, 1)                 cChange := Rand.Int (-1, 1)                 exit when (rChange ~= 0 and cChange = 0) or (rChange = 0 and cChange ~= 0)             end loop

While this is an easy way of returning a random value within a certain set of numbers, I'm not sure if it's the safest way to do so. Making an exit when statement dependent on a random number means there is a possibility of your program staying in that loop for quite some time, especially if you choose to later increase those values. It also means that the time spent in the loop isn't always going to be relatively constant, which could be a problem.

My suggestion would be to first randomly select which variable is going to be 0 and then to randomly select an element from a predefined list of values in an arrayand the assign that value to your variable. Here's a comparison of the two methods.

code:

var iNum1, iNum2, iPlaceHolder, TimeSince : int := 0 var iaSelectableValues : array 1..200 of int %array will hold selectable values %initiates values between -100 and 100 iPlaceHolder := -100 for i:1..200 iaSelectableValues (i) := iPlaceHolder iPlaceHolder +=1 end for View.Set ("text") loop %method 1 TimeSince := Time.Elapsed loop iNum1 := Rand.Int (-100, 100) iNum2 := Rand.Int (-100, 100) exit when iNum1~=0 and iNum2 = 0 exit when iNum1=0 and iNum2 ~= 0 end loop put "Time Elapsed (Method 1): ", (Time.Elapsed - TimeSince) / 1000 put iNum1, ", ", iNum2 Input.Pause %method 2 TimeSince := Time.Elapsed if Rand.Int (1 , 2) = 2 then %determine which value is going to be 0, and which is going to be a value from the array iNum1 := 0 iNum2 := iaSelectableValues (Rand.Int (1, upper (iaSelectableValues))) %randomly select an element from the array and assign it else iNum2 := 0 iNum1 := iaSelectableValues (Rand.Int (1, upper (iaSelectableValues))) end if put "Time Elapsed (Method 2): ", (Time.Elapsed - TimeSince) / 1000 put iNum1, ", ", iNum2 Input.Pause end loop

Run it through a couple times, and watch the time for method 1. Occasionally, it will be an odd number like 0.007 or something. Compare this to method 2, which stays relatively constant to two different times (0 and 0.001 for me).

[Tony]

Jorbalax wrote:

It's really hard to determine what the problem is with just that small line of coding.

Oh no, it's all there - look closer

code:

loop                 rChange := Rand.Int (-1, 1)                 cChange := Rand.Int (-1, 1)                 exit when (rChange ~= 0 and cChange = 0) or (rChange = 0 and cChange ~= 0)             end loop

rChange and cChange are our random directions, pretty simple

code:

if Rand.Real > 0.9 and map (g.r + rChange, g.c + cChange) = EMPTY then                 g.rChange := rChange                 g.cChange := cChange             end if

I don't quite understand this, but there's a 10% chance to assign g.rChange and g.cChange the random values we picked a step above, if we're allowed to move in that direction

code:

if map (g.r + rChange, g.c + cChange) = EMPTY then                 g.r += g.rChange                 g.c += g.cChange             end if

We check once again if we can move in rChange/cChange direction, and is so, proceed to go in... g.rChange / g.cChange direction instead. Though there's only a 10% chance to actually have those values the same, so 90% of the time, if a random direction is valid, the ghost will continue to proceed straight through the wall

you need

code:

if map (g.r + g.rChange, g.c + g.cChange) = EMPTY

basically look and go in the same direction.

[Aziz]

Omg I knew I had worked on it straight for too long, yeah I seen the problem before the end of the post. Thank a bunch Tony!

[Aziz]

Jorbalax wrote:

It's really hard to determine what the problem is with just that small line of coding. Perhaps you should post a bit more.

Also...

code:

loop                 rChange := Rand.Int (-1, 1)                 cChange := Rand.Int (-1, 1)                 exit when (rChange ~= 0 and cChange = 0) or (rChange = 0 and cChange ~= 0)             end loop

While this is an easy way of returning a random value within a certain set of numbers, I'm not sure if it's the safest way to do so. Making an exit when statement dependent on a random number means there is a possibility of your program staying in that loop for quite some time, especially if you choose to later increase those values. It also means that the time spent in the loop isn't always going to be relatively constant, which could be a problem.

My suggestion would be to first randomly select which variable is going to be 0 and then to randomly select an element from a predefined list of values in an arrayand the assign that value to your variable. Here's a comparison of the two methods.

code:

var iNum1, iNum2, iPlaceHolder, TimeSince : int := 0 var iaSelectableValues : array 1..200 of int %array will hold selectable values %initiates values between -100 and 100 iPlaceHolder := -100 for i:1..200 iaSelectableValues (i) := iPlaceHolder iPlaceHolder +=1 end for View.Set ("text") loop %method 1 TimeSince := Time.Elapsed loop iNum1 := Rand.Int (-100, 100) iNum2 := Rand.Int (-100, 100) exit when iNum1~=0 and iNum2 = 0 exit when iNum1=0 and iNum2 ~= 0 end loop put "Time Elapsed (Method 1): ", (Time.Elapsed - TimeSince) / 1000 put iNum1, ", ", iNum2 Input.Pause %method 2 TimeSince := Time.Elapsed if Rand.Int (1 , 2) = 2 then %determine which value is going to be 0, and which is going to be a value from the array iNum1 := 0 iNum2 := iaSelectableValues (Rand.Int (1, upper (iaSelectableValues))) %randomly select an element from the array and assign it else iNum2 := 0 iNum1 := iaSelectableValues (Rand.Int (1, upper (iaSelectableValues))) end if put "Time Elapsed (Method 2): ", (Time.Elapsed - TimeSince) / 1000 put iNum1, ", ", iNum2 Input.Pause end loop

Run it through a couple times, and watch the time for method 1. Occasionally, it will be an odd number like 0.007 or something. Compare this to method 2, which stays relatively constant to two different times (0 and 0.001 for me).

You're absolutely right. That does make sense. But in that example, there was 200 different possibilities. I made it with only 2, and both methods were about the same. However, I am going to incorporate this into pacman and remember it for future use, as I have used this method (method #1 in the example) before and I think it is a lot better. Just pointing out that it didn't make much of i difference, but I do understand and you're wholly correct. (hahah....hole)

code:

var iNum1, iNum2, iPlaceHolder, TimeSince : int := 0 var iaSelectableValues : array 1 .. 2 of int %array will hold selectable values iaSelectableValues (1) := -1 iaSelectableValues (2) := 1 View.Set ("text") loop     %method 1     TimeSince := Time.Elapsed     loop         iNum1 := Rand.Int (-1, 1)         iNum2 := Rand.Int (-1, 1)         exit when iNum1 ~= 0 and iNum2 = 0 or iNum1 = 0 and iNum2 ~= 0     end loop     put "Time Elapsed (Method 1): ", (Time.Elapsed - TimeSince) / 1000     put iNum1, ", ", iNum2     Input.Pause     %method 2     TimeSince := Time.Elapsed     if Rand.Int (1, 2) = 2 then %determine which value is going to be 0, and which is going to be a value from the array         iNum1 := 0         iNum2 := iaSelectableValues (Rand.Int (1, upper (iaSelectableValues))) %randomly select an element from the array and assign it     else         iNum2 := 0         iNum1 := iaSelectableValues (Rand.Int (1, upper (iaSelectableValues)))     end if     put "Time Elapsed (Method 2): ", (Time.Elapsed - TimeSince) / 1000     put iNum1, ", ", iNum2     Input.Pause end loop