Example CoordinatesArray subclass

RouteCoordinatesArray.js

class RouteCoordinatesArray extends Animated.CoordinatesArray {
  newCoordAnimator(config, origCoords) {
    const {along} = config;

    return {
      dist: along[0],
      distconf: along[1],

      calculate(progress, coords) {
        const currentDist = progress * this.dist;

        let prevsum = 0;
        let actsum = 0;
        let i = origCoords.length - 1;
        while (actsum < currentDist && i > 0) {
          prevsum = actsum;
          actsum += distance(
            point(coords[i]),
            point(coords[i - 1]),
            this.distconf,
          );
          i -= 1;
        }
        if (actsum <= currentDist) {
          return [coords[0]];
        }
        const r = (currentDist - prevsum) / (actsum - prevsum);
        const or = 1.0 - r;

        return [
          ...coords.slice(0, i + 1),
          [
            coords[i][0] * r + coords[i + 1][0] * or,
            coords[i][1] * r + coords[i + 1][1] * or,
          ],
        ];
      },
    };
  }
}