excalidraw/src/gesture.ts

import { PointerCoords } from "./types";
import { normalizeScroll } from "./scene";

export function getCenter(pointers: Map<number, PointerCoords>) {
  const allCoords = Array.from(pointers.values());
  return {
    x: normalizeScroll(sum(allCoords, coords => coords.x) / allCoords.length),
    y: normalizeScroll(sum(allCoords, coords => coords.y) / allCoords.length),
  };
}

export function getDistance([a, b]: readonly PointerCoords[]) {
  return Math.hypot(a.x - b.x, a.y - b.y);
}

function sum<T>(array: readonly T[], mapper: (item: T) => number): number {
  return array.reduce((acc, item) => acc + mapper(item), 0);
}