Fast AI

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Summary:

Fast random AI

Fast AI

Myles_Zadok 04 Sep 2017 23:31

So I was thinking about improving the Pong game I made, and I noticed that the game mode that uses AI is a little slower than the endless score mode. I was wondering if anyone had ideas on how to make an AI that isn't unbeatable, but also isn't super dumb. Here is the code of the AI in my Pong game:

randInt(1,100)→M
If M≤55
Then
If H=5
Then
If (D+5)>J and J≠140
Then
Line(240,I,240,J,0)
I+3H→I
J+3H→J
Line(240,I,240,J,RED)
Else
Line(240,I,240,J,RED)
End
End
If H=­5
Then
If (D-5)<I and I≠20
Then
Line(240,I,240,J,0)
I+3H→I
J+3H→J
Line(240,I,240,J,RED)
Else
Line(240,I,240,J,RED)
End
End
Else
Line(240,I,240,J,RED)
End

I think the biggest thing that slows the game down is the random integer command, but I haven't thought of an alternative to my method.

Re: Fast AI

Timothy Foster 04 Sep 2017 23:57

What does the random number do? The simplest AI will simply try to match the vertical position of the ball, and it's surprisingly effective while still beatable.

---

Timothy Foster - @tfAuroratide
Auroratide.com - Go here if you're nerdy like me

Re: Fast AI

Myles_Zadok 05 Sep 2017 01:21

The AI paddle moves only when the random number is less than 55. Since the game loop is a Repeat loop, this is repeated every "frame" (for lack of better word), so the paddle moves only on 55% of the frames. This prevents the AI from being unbeatable, but also from being too easy. H is the previous y-velocity of the ball. The code takes that, compares it with the current y-position of the ball, and determines whether the future position of the ball will be above or below it, then (if M=55 or less) moves accordingly.

Last edited on 05 Sep 2017 01:22 by Myles_Zadok Show more

Re: Fast AI

Battlesquid 05 Sep 2017 01:40

I also think that the AI that follows the ball's y-position is efficient, yet beatable. However, if you want to use your method, you might want to increase that percentage (I think 65-75% is pretty good).

What does H represent?

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Re: Fast AI

Myles_Zadok 05 Sep 2017 02:22

H is the y-velocity of the ball. H has a value of either 5 or -5, which is the velocity of the ball. That value is stored to the y-position of the ball once per frame, making the ball move up or down. It has been awhile since I wrote my code, so I only remember so much of how it worked right off the top of my head, hence why I thought there was a previous velocity (there probably isn't). The AI I have essentially follows the ball's y-position, but since it moves after the ball does within a frame, it has to project where the ball will be on the next frame, and move there.

When I played around with the percentages, I found anything over 65% to essentially be unbeatable. The paddle only moves on 55% of the frames, so it returns the ball about 90% of the time (my off-the-top-of-my-head approximation). The range from 50% to 65% is the only time the difficulty really changes, as anything less than 50 is way too easy, but anything above 65 is unbeatable.

My initial AI tried to match the position of the ball, but that would almost never return the ball, since it would move after the ball within a frame, so the ball would go just above or below the paddle nearly every time. That may have been the result of poor coding on my part, however. I would be interested to see a AI with different code than mine in a pong game.

Re: Fast AI

Timothy Foster 05 Sep 2017 03:19

It sounds like what you are really wanting is the paddle to move about half as fast as normal speed. You're currently accomplishing this with random numbers, but you could also change the velocity scaling factor for the paddle's movement.

I assume the following lines of code move the paddle:

I+3H→I
J+3H→J

Instead of moving the paddle by 3H, you could move it by 1.5H and achieve the speed scaling I think you want. Then, you wouldn't need to use random numbers. I don't know the full context of your program, though, so my methodology here might not fit your precise needs.

I don't have a TI-Basic pong game, but I wrote one in Haxe a long time ago. The basic AI just follows the ball.

---

Timothy Foster - @tfAuroratide
Auroratide.com - Go here if you're nerdy like me

Last edited on 05 Sep 2017 03:27 by Timothy Foster Show more

Re: Fast AI

Trenly 05 Sep 2017 03:17

You had said "I think the biggest thing that slows the game down is the random integer command, but I haven't thought of an alternative to my method." I am wondering if anyone has ever run a speed comparison between RandInt( and rand. The reason for this is the following: $RandInt(1,100)=int(100rand$. Since you are only checking if the number is greater than or equal to 55, you can drop the $int($ leaving just $100rand≤55$. This can be simplified even more, by dividing both sides by 100 such that you only need to check $rand≤.55$. Doing that you don't need to store the variable, so your code could be:

If rand≤.55
Then
If H=5
Then
If (D+5)>J and J≠140
Then
Line(240,I,240,J,0)
I+3H→I
J+3H→J
Line(240,I,240,J,RED)
Else
Line(240,I,240,J,RED)
End
End
If H=­5
Then
If (D-5)<I and I≠20
Then
Line(240,I,240,J,0)
I+3H→I
J+3H→J
Line(240,I,240,J,RED)
Else
Line(240,I,240,J,RED)
End
End
Else
Line(240,I,240,J,RED)
End

Edit:
These are the timings I got.

Iterations	RandInt	rand
100	.198	.198
200	.199	.199
500	.219	.199
1000	.229	.189

Last edited on 05 Sep 2017 03:51 by Trenly Show more

Re: Fast AI

lirtosiast 05 Sep 2017 08:48

Yep, rand in any form takes about 15 ms per call, and the internal multiplication and addition of a + rand*(b-a) of randInt(a,b takes a few more ms. Better would be Timothy Foster's solution or something that moves the paddle periodically, like a "If fPart(X)<.55" where X is incremented by .55 each generation.

Re: Fast AI

Myles_Zadok 05 Sep 2017 16:04

I may look into doing what Timothy Foster suggested, since that would appear to make a better AI than the one I made, but I think Trenly gave me a good solution. The Pong game I made has two modes: one versus an AI, and another where the player tries to return the ball against a wall as many times as possible. The second mode runs a little faster than the first, and the only difference between the two is the AI in the first mode. The only thing in the AI that I thought would slow down the first mode was randInt, so if I use rand instead, that may speed up the program enough so that it will run at the same speed as the other game mode.

Re: Fast AI

Myles_Zadok 08 Oct 2017 22:04

UPDATE: I finally got around to updating Pong CE, and the solution Trenly provided works very well. There is no longer a frame rate difference between the two game modes.

Re: Fast AI

Trenly 08 Oct 2017 23:42

Sometimes the simplest solutions are the best