Games

Map geometry

Build maps and test positions with plain-data shapes from disko:geometry.

The physics world handles collisions for you, but games still need geometry of their own: placing walls in a circle, putting posts at the corners of a hexagon, checking whether a player is standing inside the center circle. disko:geometry gives you the math for that.

Shapes are just data

The shapes in disko:geometry are plain objects, not things in the world:

a point is { x, y };
a segment is { start, end };
a circle is { center, radius };
an arc is { start, end, curve }.

Creating a shape doesn't add anything to the match. You use shapes to compute positions, then pass the results to world.create… functions. And because these functions don't depend on the world, you can call them anywhere, including top-level code, and they give the same answer on every computer.

Curved walls with arcs

A wall in the world can be straight or curved. A curved wall is described by its two ends and a single number, curve, that says how much it bends:

curve: 0 bends the wall into a half circle;
a positive curve is a gentler bend (less than half a circle);
a negative curve bends past half a circle.

Working that number out by hand is fiddly. arcFromCenter does it for you: give it a center, a radius, a start angle and how far around to sweep, and it returns start, end and curve, exactly the values world.createSegment takes. This builds a round arena out of eight arcs, and six posts in a hexagon:

src/arena.ts

game.on("start", () => {
  // A circular arena wall out of 8 world arcs.
  for (let i = 0; i < 8; i++) {
    const arc = arcFromCenter({
      center: vec(0, 0),
      radius: 300,
      startAngle: (i * TAU) / 8,
      sweep: TAU / 8,
    });

    world.createSegment({
      start: world.createVertex(arc.start),
      end: world.createVertex(arc.end),
      curve: arc.curve,
    });
  }

  // Six static corner posts.
  for (const post of regularPolygon({
    center: vec(0, 0),
    radius: 120,
    sides: 6,
  })) {
    world.createVertex(post);
  }
});

Asking questions about positions

The other half of the module answers questions: where do two lines cross, how far is a point from a wall, is a point inside a shape. This checks every tick whether a player is inside the center circle:

src/rules.ts

const centerCircle = circle(vec(0, 0), 60);

game.on("tick", () => {
  for (const player of game.players) {
    const position = player.controlledObject?.state().position;

    if (position !== undefined && circleContainsPoint(centerCircle, position)) {
      // The player is inside the center circle.
    }
  }
});

The module covers:

Intersections: segmentIntersection, lineCircleIntersections, rayArcIntersection and more.
Distances and closest points: to lines, segments, circles and arcs.
Bounds: the box around a shape, and whether two boxes overlap.
Containment: whether a point is inside a circle, a box or a polygon.

How answers are returned

A question with at most one answer returns it, or null if there's none.
A question with up to two answers, such as where a line meets a circle, returns an array, ordered along the first shape.
Points exactly on a boundary count as inside.
Comparisons are exact. Add a last argument { epsilon } to allow a small margin of error.
A polygon is an array of three or more points.

See the disko:geometry reference for every function.