Generation and Render of 2D Map with Terrain in Dart + Flutter. Adding Forest Spots. Part 2


In Part 1 we created all needed methods to generate map with Grass and River. In this part we will add Forest spots to the map. A lot of code is reused from Part 1 but it is gradually enhanced step-by-step.

Final Result

The forest is added in different points and different shapes: Screenshot_1599894575.png


Refactor previous methods

Before we start jumping into Forest, we need to enhance code written in previous part.

One of the things I did not like about it was that we directly accessed tiles list via indexes. We had to play with rows/columns/x/y variables and place them into correct spots.

With refactoring all manipulations with tiles is now done via special methods:

  MapTile tileAtPoint(Point point) {
    return tiles[point.y][point.x];

  void setTileAtPoint(Point point, MapTile tile) {
    tiles[point.y][point.x] = tile;

  void setTile(MapTile tile) {
    tiles[tile.y][tile.x] = tile;

We no longer operate with pure x/y/row/col variables. All coordinates are instances of class Point (from dart:math).

For example, getting random point on map returns Point:

  Point _getRandomPoint() {
    var col = Random().nextInt(width - 1);
    var row = Random().nextInt(height - 1);
    return Point(col, row);

With these enhancements the code looks less mathy and more OOPish.

Forest specifications

  • Forest can occupy empty tiles (that are currently grass)
  • It cannot occupy or cross the river
  • Forest can grow in other not yet occupied tiles.

addForest method

Implementing these requirements is pretty straightforward given that you also already wrote some useful utility functions :)

  void addForest() {
    ForestMapTile forest;

    // amount of tries to pick the spot for forest
    var tries = 10;
    while (tries-- > 0) {
      var point = _getRandomPoint();
      var tile = tileAtPoint(point);
      if (tile.type != MAP_TILE_TYPES.GRASS) {
      // first tile of the new forest spot
      forest = ForestMapTile(x: point.x, y: point.y);

      // with 75% change grow the forest in random direction
      while (willGrow(75)) {
        var nextPoint = _nextPoint(Point(forest.x, forest.y));
        var nextTile = tileAtPoint(nextPoint);
        if (nextTile.type == MAP_TILE_TYPES.GRASS) {
          forest = ForestMapTile(x: nextPoint.x, y: nextPoint.y);
          setTileAtPoint(nextPoint, forest);
      // forest growing is done

willGrow method is enhanced and allows to provide % for success as input argument

  bool willGrow(int chance) {
    var next = Random().nextInt(100);
    return next <= chance;

Another useful method is _nextPoint. It returns a nearby point to the given input point:

Point _nextPoint(Point point) {
    var decision = leftDownRight();
    var nextX = point.x;
    var nextY = point.y;
    if (decision == 0) {
      nextY = nextY + 1;
    if (decision == -1) {
      nextX = nextX - 1;
    if (decision == 1) {
      nextX = nextX + 1;
    // truncate out of bounds values back to point inside the map
    if (nextX >= width) {
      nextX = width - 1;

    if (nextY >= height) {
      nextY = height - 1;

    if (nextX < 0) {
      nextX = 0;

    if (nextY < 0) {
      nextY = 0;

    return Point(nextX, nextY);

Adding forest to the map

Another method addForests is used to generate multiple forest spots:

  void addForests() {

timesRepeat is an Extension for int type:

extension TimesRepeat on int {
  void timesRepeat(Function f) {
    for (var i = 0; i < this; i++) {

Create map with river and forest

Now you can call addRiver and addForests methods to initialize map:

final WorldMap map = WorldMap(width: 20, height: 20)

The map generated map looks something like this: Screenshot_1599896050.png


In Part 3 we will generate lakes and further refactor existing functions. Stay tuned!

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