flowfield/FlowField.js

This library provides a pathfinding mechanism based on vectors field.

/* @flow */
import filter from 'lodash.filter';
import map from 'lodash.map';
import minBy from 'lodash.minby';
import { Map, List, Range } from 'immutable';

import type { Cell, Grid, FlowField, UpdateFunction, Position } from './types';

import utils from './basicFunctions';

export function create(step: number, height: number, width: number): FlowField {
  const xRange: number = Math.ceil(width / step);
  const yRange: number = Math.ceil(height / step);
  const outOfBounds: Function = utils.generateOutOfBoundsFunction(
    xRange,
    yRange
  );

  let target: ?Position;

  let grid: Grid = List(Range(0, xRange)).map((): List<Cell> =>
    List(Range(0, yRange)).map((): Cell =>
      Map({
        distance: -1,
        updated: false,
        direction: [0, 0],
        obstacle: false
      })
    )
  );
  function updateDistance(): Grid {
    if (!target || target.length !== 2) {
      return grid;
    }
    grid = grid.map((row: List<Cell>): List<Cell> =>
      row.map((cell: Cell): Cell => {
        const isItTheTarget: boolean = cell.get('distance') === 0;
        const isItAnObstacle: boolean = cell.get('obstacle');
        return isItAnObstacle || isItTheTarget
          ? cell
          : cell.set('updated', false);
      })
    );
    let distance: number = 1;
    let tilesToUpdate: List<Position> = List();
    tilesToUpdate = tilesToUpdate.push(target);
    do {
      const neighbours: List<Position> = tilesToUpdate
        .map((position: Position): List<Position> => {
          return List(utils.getNeighbours(position, outOfBounds, grid));
        })
        .flatten();

      tilesToUpdate = tilesToUpdate.clear();
      neighbours.forEach((position: Position): void => {
        const cell = grid.getIn(position);
        if (cell && !cell.get('updated')) {
          grid = grid.setIn(
            position,
            cell.merge(Map({ distance, updated: true }))
          );
          tilesToUpdate = tilesToUpdate.push(position);
        }
      });
      distance = distance + 1;
    } while (tilesToUpdate.size > 0);
    return grid;
  }
  function updateVectorField(grid: Grid): Grid {
    if (!target || target.length !== 2) {
      return grid;
    }
    let newGrid: Grid = grid.map((row, i) => {
      return row.map((cell, j) => {
        if (cell.get('distance') === 0 || cell.get('obstacle')) {
          return cell;
        }
        //Vector from current cell to Target
        const toTarget: Array<number> = [target[0] - i, target[1] - j];

        //Get All neightbours for current cell
        let neighbours: Array<Cell> = utils
          .getNeighbours([i, j], outOfBounds, grid)
          .map((position: Position): Object => ({
            cell: grid.getIn(position),
            position
          }))
          .filter((props: Object): boolean => !props.cell.get('obstacle'));

        //Get minimum distance
        let minimumDistance: number = minBy(
          neighbours,
          (props: Object): number => props.cell.get('distance')
        ).cell.get('distance');

        //Get only cell with their distance equals to minimum
        const validNeighbours = neighbours
          .filter(
            (props: Object) => props.cell.get('distance') === minimumDistance
          )
          //Calculate heading to target from each possible cell
          .map(({ cell, position }) => {
            return [
              (target[1] - position[1]) * (target[1] - position[1]) +
                (target[0] - position[0]) * (target[0] - position[0]),
              position
            ];
          });
        const cellClosestToTarget: Position = minBy(
          validNeighbours,
          ([angle, position]) => angle
        )[1];
        return cell.set('direction', [
          cellClosestToTarget[0] - i,
          cellClosestToTarget[1] - j
        ]);
      });
    });
    grid = newGrid;
    return grid;
  }
  function updateGrid(): Grid {
    return updateVectorField(updateDistance());
  }
  return {
    getImmutableGrid(): Grid {
      return grid;
    },
    getGrid(): Array<Array<Object>> {
      return grid.toJS();
    },
    getCell(position: Position): ?Object {
      if (outOfBounds(position)) {
        return undefined;
      }
      const cell = grid.getIn(position);
      return cell ? cell.toJS() : undefined;
    },
    getCellFromRealWorldCoordinates(position: Position): ?Object {
      const positionInLocalWorld: Position = position.map(coord =>
        Math.floor(coord / step)
      );
      if (outOfBounds(positionInLocalWorld)) {
        return undefined;
      }
      const cell: ?Cell = grid.getIn(positionInLocalWorld);
      return cell ? cell.toJS() : undefined;
    },
    setObstacle(obstacle: Position): Grid {
      if (outOfBounds(obstacle)) {
        return grid;
      }
      const cell: ?Cell = grid.getIn(obstacle);
      if (cell) {
        const updatedCell: Cell = cell.merge(
          Map({
            obstacle: true,
            distance: -1,
            updated: true,
            direction: [0, 0]
          })
        );
        grid = grid.setIn(obstacle, updatedCell);
      }
      grid = updateGrid();
      return grid;
    },
    removeObstacle(obstacle: Position): Grid {
      if (outOfBounds(obstacle)) {
        return grid;
      }
      const cell: ?Cell = grid.getIn(obstacle);
      if (!cell) {
        return grid;
      }
      const updatedCell: Cell = cell.merge(
        Map({
          obstacle: false,
          distance: 0,
          updated: false,
          direction: [0, 0]
        })
      );
      grid = grid.setIn(obstacle, updatedCell);

      grid = updateGrid();
      return grid.toJS();
    },
    setTarget(newTarget: Position): Grid {
      if (outOfBounds(newTarget)) {
        return grid;
      }
      const newTargetCell: ?Cell = grid.getIn(newTarget);
      if (!newTargetCell) {
        return grid;
      }
      if (target) {
        const targetCell: ?Cell = grid.getIn(target);
        if (!targetCell) {
          return grid;
        }
        const cellReset: Cell = targetCell.merge(
          Map({
            updated: false,
            distance: -1,
            obstacle: false,
            direction: [0, 0]
          })
        );
        grid = grid.setIn(target, cellReset);
      }

      const targetSet: Cell = newTargetCell.merge(
        Map({
          distance: 0,
          updated: true,
          obstacle: false,
          direction: [0, 0]
        })
      );
      grid = grid.setIn(newTarget, targetSet);
      target = newTarget;
      grid = updateGrid();
      return grid.toJS();
    },
    getTarget(): ?Position {
      return target;
    },
    getPathFromCoordinates(startPosition: Position): Array<Position> {
      if (outOfBounds(startPosition) || !target) {
        return [];
      }
      const startingCell: Cell = grid.getIn(startPosition);
      const cellsToGoThrough = Range(1, startingCell.get('distance')).reduce(
        (acc: Array<Position>, distance: Number) => {
          const direction = grid.getIn(acc[acc.length - 1]).get('direction');
          return [
            ...acc,
            [
              acc[acc.length - 1][0] + direction[0],
              acc[acc.length - 1][1] + direction[1]
            ]
          ];
        },
        [startPosition]
      );
      return [...cellsToGoThrough, target];
    }
  };
}