The rules of Triangles

In brief

Players take turns drawing a line between two stars. A line must not cross another line or pass over a star. Closing a triangle that contains no star scores one point. The game ends when no more triangles can be closed; whoever has the most triangles wins.

The goal

Close more triangles than your opponent. The board is a cloud of stars: 24, 60 and 120 stars on phone, 80, 120 and 180 on tablet, depending on the board chosen. There is no grid: a line can connect two distant stars, as long as it follows the rules below.

Drawing a line

Tap one star, then another, or drag from one star to the other. The line takes the player's color: with the Nebula theme, the default one, orange-red for Player 1 and blue for Player 2. The app rejects a line in three cases:

it already exists;
it passes over another star (by a hair: the app allows a margin of a few screen points at most);
it crosses a line that has already been drawn. Two lines can start from the same star, but they can never cross.

Line B–D (dotted) is rejected: it would cross line A–C.

Line A–C (dotted) is rejected: it would pass over star B.

When a triangle counts

When your line closes a triangle, meaning the other two sides are already drawn (by you or by your opponent), the triangle fills with your color and you score a point. A triangle counts only if it contains no star, neither inside it nor exactly on a side. Its three sides can be drawn, but it scores nothing.

The large triangle ABC is closed, but star D is inside it: no point.

The small triangles around D, however, do count.

One line, two triangles

A line has two sides: it can close a triangle on each side and score 2 points at once. On the square below, the diagonal A–C closes both ABC and ACD.

The diagonal A–C closes two triangles at once.

The "Play again after a triangle" option

By default, each player draws one line per turn, whether or not it closes a triangle. In the New game window, the "Play again after a triangle" option changes this: a player who closes at least one triangle immediately draws another line. In the example, Player 1 closes a triangle on move 3 and plays again on the next move.

The end of the game

The app ends the game as soon as no triangle can be closed and counted any more: any line that would still be possible would score nothing. The player who has closed the most triangles wins. Against the computer, the end screen shows "You won!" or "You lost!"; in two-player mode, it names the winner.

A tie

With an equal number of triangles, the end screen shows "Tie!". Against the computer, a tie counts as neither a win nor a loss in the statistics. See the example that ends in a tie.