As a follow-up to static binary translation of arcade games to JavaScript, this talk is about the interesting ways to implement simple AI for oponent cars in the classic racing game "Sprint" and how this led me to modern robotics research like the potential field method.

1. Sprint - Exciting Insights
from Translating an Old
Videogame to JavaScript
Norbert Kehrer
ViennaJS Meetup, March 30, 2016

2. „Sprint“ is a primitive car-racing game,
but it holds interesting aspects
 Atari 1976: Sprint 2
 Arcade machine
 Very limited hardware
 Black-and-white graphics
 Many sequels

3. This is what Sprint looks like

4. Fun with Sprint
 Make a browser game
 Make it 3D
 Understand the car AI
 Design new levels
 Use the methods in other projects

5. Fun with Sprint
 Make a browser game
 Make it 3D
 Understand the car AI
 Design new levels
 Use the methods in other projects

6. The Sprint arcade machine is based on the
6502 microprocessor
ROM:
Program and
12 race tracks
RAM
128 bytes
Screen RAM
32 x 286502
Special-purpose
video
hardware
Game logic Video hardware

7. Original 6502 code translated to JavaScript
makes up a browser game
ROM:
program
and 12 race tracks
RAM
128 bytes
Screen memory
32 x 286502
Special-purpose
video
hardware
Game logic Video hardware
JavaScript
program
JS simulator of the
video hardware
Browser game

8. Fun with Sprint
 Make a browser game
 Make it 3D
 Understand the car AI
 Design new levels
 Use the methods in other projects

9. Alternative interpretation of the game state
and screen memory makes it a 3D game
Little
Cubes
3D Objects
Camera

10. Fun with Sprint
 Make a browser game
 Make it 3D
 Understand the car AI
 Design new levels
 Use the methods in other projects

11. Atari‘s patented method from 1976 ...

12. ... uses direction vectors

13. Compare the car´s current direction with
the cell´s direction guidance vector...

14. ... and steer a little bit in that direction

15. Fun with Sprint
 Make a browser game
 Make it 3D
 Understand the car AI
 Design new levels
 Use the methods in other projects

16. Sprint contains twelve tediously
hand-crafted race tracks

17. Designing new Sprint levels is a lot of work
Design the race track itself
Define all those
direction vectors
Test it

18. Automation is a quite hard robotics problem
Design the race track itself
Define all those
direction vectors
Test it
Automatically
by using the
potential field
method

19. Concepts of the potential field method
 Potential field
 Vector field
 Gradient field

20. Functions
x
y = f(x)

21. Scalar fields (potential fields)
1
5
9
13
17
21
25
29
R1
R7
R13
R19
R25
R31
-450
-400
-350
-300
-250
-200
-150
-100
-50
0
z = f(x, y)

22. Vector fields
x
y z = f (x, y)

23. The gradient field indicates the direction of
the steepest slope
Source: „Kurs: Mathematik für Anwender (Osnabrück 2011-2012)“

24. Robot path planing by finding an adequate
potential field
Source: Diemke: „Pfadplanung mit harmonischen
Potentialfeldern“

25. Sprint levels are gradient fields of
„Bobsled tracks“

26. The lateral and downhill slope definies the
potential field

27. The potential field of level 1
1
6
11
16
21
26
31
R1
R6
R11
R16
R21
R26
-1
-0,5
0
0,5
1

28. Applying the potential field method to Sprint
 Obstacles are given (track boundaries)
 Calculate a harmonic potential field („bobsled track“)
 From that, calculate its gradient field
 The result is the vector field for the Sprint level

29. Level 1 by the Atari Engineers

30. Level 1, automatically generated

31. New level, automatically generated

32. The calculation is not fast, but slow
 Complex mathematics
 BUT: Unbelievably simple algorithm (Gauss 1823 und
Seidel 1874)
 64-bit floating-point numbers are not exact enough 
BigNumber library needed
 Slow also because of iteration (30 seconds per level)

33. Fun with Sprint
 Make a browser game
 Make it 3D
 Understand the car AI
 Design new levels
 Use the methods in other projects

34. You can use the potential field method
 Path planning for robots
Lawn mowers
Vacuum cleaners
Robo soccer
Autonomous cars
 Games with moving computer oponents
Car racing
Mario-Kart-like games
Etc.

35. Summary
 Browser Sprint by code translation
 3D Sprint by alternative interpretation
 Patented vector fields for the car AI
 Automatic level generation with the Potential Field Method

36. Thank you !
http://members.aon.at/nkehrer/