Pipe masks and water rules

Masks and positions

A pipe mask uses four bits: north 1, east 2, south 4, west 8. turn rotates those bits; opposite instead accepts a side index from 0 to 3. Cells are zero-based in row-major order. A native code includes dimensions, masks, sources, drains and twists, so a code is more than an image of pipes.

import {NORTH,EAST,turn,opposite,shapeOf} from "@johnmorrisdotca/suido";
const elbow = NORTH | EAST;
console.log(elbow,turn(elbow),shapeOf(elbow),opposite(0));

3 6 elbow 2

The board's kind decides completion

A network must wet every pipe with no leak. A drains board must reach every drain with no leak from its wet pipes; spare dry pipes need not be used. An inlet-outlet board asks for one unbranched path between its endpoints. flowOf exposes wet cells, traversal depths and spills, and isSolved uses these native rules. Matching two adjacent openings alone is insufficient.

A big piece occupies a 2×2 square. A block turn moves all four cells around the square and turns their masks together; it is not four independent rotations. Locked cells and walls constrain legal answers. The shipped classic ladder stays fixed; the separate big-piece set supplies its own boards. See the pieces, twists and architecture.