WebGL2 is needed to draw the board
The whole game runs on your own machine; nothing is sent anywhere. Try a current desktop browser with hardware acceleration enabled.
The whole game runs on your own machine; nothing is sent anywhere. Try a current desktop browser with hardware acceleration enabled.
Carrom is a traditional board game of the Indian subcontinent. It has no documented inventor — the earliest sources disagree about where it came from, and the ICF's own account says only that it is "thought to have originated from pool billiard about 150 years ago in Indian sub-continent". Serious tournaments may have begun in Sri Lanka in 1935; India and Sri Lanka both had federations by 1958. The International Carrom Federation was formed in October 1988 in Madras (now Chennai), India, at the first World Carrom Congress, where the Laws of Carrom were codified; the edition this game follows is stamped 1993.
This is an independent reimplementation. It is not affiliated with the
International Carrom Federation or with any commercial carrom app, uses none of their artwork,
branding or code, and reproduces only the published rules and dimensions, which are facts
about the game rather than anyone's creative work. The board you see is drawn from those
dimensions by code in js/boardtex.js, not copied from a photograph.
| Playing surface | 73.75 cm square (the Laws allow 73.50–74.00) |
|---|---|
| Frame | breadth 6.98 cm, standing 2.22 cm above the surface |
| Pockets | 4.45 cm across, rounded inwardly at each corner |
| Base lines | two per side, 10.15 cm from the frame and 3.18 cm apart, 47.09 cm tip to tip |
| Base circles | 3.18 cm across, with a 2.54 cm red centre |
| Centre Circle | 3.18 cm, red |
| Outer Circle | 17.00 cm — not decoration: every returned man is placed inside it |
| Arrows | 45°, at most 0.15 cm thick, stopping 5.00 cm clear of the pocket |
| Carrom men | 3.10 cm across, 0.80 cm thick, 5.25 g — nine white, nine black, one red queen |
| Striker | 4.13 cm, 15.00 g. The Laws give a ceiling and no minimum for either. |
The winner of a board scores the number of the opponent's men still on it, one point each, plus 3 for the queen if the winner covered it and is still under 22 points. A board is capped at 12 points (Rule 55) — the widely quoted "25 maximum" is the game target, not a board cap. A game is 25 points or 8 boards, whichever comes first, and a match is the best of three games.
Many disc-and-friction games decay a piece's sliding and its spinning as two separate processes. That is not how a disc on a flat dry surface behaves. Integrating Coulomb friction over the whole contact area gives a force and a torque that depend on the state only through the single ratio ε = v/(Rω), so the two motions are locked together. The ratio is pulled onto a universal attractor — for a uniform disc 0.653002 — and translation and rotation then run down linearly and reach zero at the same instant.
Two consequences you can feel while playing. A coin with a lot of spin is braked far less hard: at the attractor the retarding force is 0.616 of μmg rather than all of it, and a heavily spun coin travels several times as far as a dead one struck at the same speed. And a spinning coin still runs dead straight — the lateral force on an axisymmetric disc vanishes identically, so there is no curve to hunt for.
The result is not new. Ishlinskii, Sokolov and Chernousko had it in 1981; Voyenli and Eriksen corrected the constant to 0.65 in On the motion of an ice hockey puck (1985); Goyal, Ruina and Papadopoulos gave 0.653 and the general classification in 1991; Farkas, Bartels, Unger and Wolf published the closed form and a measurement in Phys. Rev. Lett. 90, 248302 (2003). This game uses that closed form with the erratum applied — the printed torque formula is wrong by a factor ε² on one branch, as Weidman and Malhotra point out in print — and checks it against an independent numerical integration of the original area integral.
From the Laws (documented): every board and piece dimension above; the opening arrangement; Rule 130's placement clauses; the queen-and-cover rules; the due and foul scheme; the scoring, the 12-point board cap, the 25-point game and the best-of-three match.
Reconstructed, because no source states them: the friction coefficient and the restitutions. The Laws give exactly one physical observable — a board must allow "at least three and a half runs" of a 15 g striker struck at maximum force — and that single equation constrains the combination of friction, cushion restitution and maximum striker speed rather than any one of them. The values here sit on that locus. Also reconstructed: the striker's thickness (the Laws never state one), the exact shape of the pocket cut, and the criterion for a man to fall in.
Deliberately not modelled, and sourced as such: a carrom man is a short cylinder, not an infinitely thin disc, and Farkas et al. note that a cylinder of finite height shifts its contact pressure forward under braking and therefore curves slightly in the direction v×ω. No formula for that is given anywhere we could find, and nobody has measured it for carrom, so the game models the axisymmetric case, in which the path is provably exactly straight.
Also simplified. There is no umpire, no clock (the Laws allow 15 seconds a stroke), no doubles, no trial boards, and returned men are placed automatically rather than by the opponent's hand. Men do not stand on their rims or rest on one another, as Rules 67 and 68 allow.
Carrom is a traditional game in the public domain with no known author. The rules and
dimensions follow the Laws of Carrom adopted by the International Carrom Federation
(formed Madras, October 1988; this edition 1993), read from the verbatim transcription published
by the UK Carrom Federation and cross-checked against two archived copies of carrom.org that are
byte-identical to each other. This reimplementation is not endorsed by, affiliated with or
connected to the ICF or any national federation. Full provenance, including everything that could
not be sourced, is in CREDITS.txt and facts.md.