I am making a 2d top-down tile based game, which is randomly generated each new world.

What I want to do is create a Polygon (or other more appropriate shape I don't know of) for each landmass not disrupted by land, basically each unseparated landmass/island, I want to do this for where my player is to spawn in the world, I want to have it so it has a higher chance of spawning on the biggest landmass in the world, rather than spawning on a tiny several tile island. So, all I need to know is how would I create some sort of shape system to recognise different islands.

The reason I suggest a Polygon is because the player would randomly spawn in that area so it has to be accurate to the land, it can't start of by spawning in water nearby.

If a Polygon is obsolete for this idea, and another system would be better let me know.

  • \$\begingroup\$ This sounds like a simple connected component search problem, which we've answered here before. Where have you run into difficulty implementing it? \$\endgroup\$
    – DMGregory
    Sep 17, 2019 at 19:13
  • \$\begingroup\$ @DMGregory I haven't tried anything yet, but I don't actually know where to start, my quesion was asking for ideas to my problem \$\endgroup\$
    – tygzy
    Sep 18, 2019 at 15:42

1 Answer 1


For the main island I would do something like this. I would choose how many sides the polygon has to have. Then, I would choose a value, how far the farthest point of the island can be. Then I would create an array of coordinates of my polygon like this:

public class Island{

    public static void main(String[] args){

        int numberOfPoints = 10;
        float [][] islandCoordinates = float[numberOfPoints][2];//array of coordinates
        float maxDistance = 1000;

        float stepAngle = 2 * Math.PI / numberOfPoints;

        for(int i = 0;  i < numberOfPoints; i++){
            float dist = maxDistance * Math.random();
            float xcoordinate = Math.cos(stepAngle * i) * dist;
            float ycoordinate = Math.sin(stepAngle * i) * dist;

            islandCoordinates[i][0] = xcoordinate;
            islandCoordinates[i][1] = ycoordinate;



This would make the island look very simple, but I think with playing with the values you could make it a lot nicer.

Good luck!


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