Smoothing randomly generated terrain in Java for a realistic effect

Question

I would like help in smoothing my random terrain out to make it look more realistic. At the moment I'm just assigning random values to an array and setting tiles to the values stored in the array.

This gives this effect:

protected void generateLevel() {
    for (int y = 0; y < height; y++) {
        for (int x = 0; x < width; x++) {
            int rand = random.nextInt(1000); //height
            if(rand <= 300){ //water level
                tiles[x + y * width] = 6;//set water
            }else{
                tiles[x + y * width] = 1; //set grass
            }
        }   
   }   
}

Please help me in making my terrain look more realistic, I would like someones opinion on how they might implement this into their game or mine. How do I smooth my terrain for a realistic effect?

Answer 1

Instead of using random-for-each-point terrain, you may consider using perlin or simplex noise instead. This has the benefit of being smooth, replicable no matter in what order you read your map, and replicable with a given starting "shuffled array". A very good description and implementation is available at this post.

Answer 2

Use OpenSimplex noise: https://gist.github.com/KdotJPG/b1270127455a94ac5d19

Do sommething like:

protected void generateLevel() {
    OpenSimplexNoise noise = new OpenSimplexNoise(); //optionally pass in a seed.
    for (int y = 0 y < height; y++) {
        for (int x = 0; x < width; x++) {
            double value = noise.eval(x / 24.0, y / 24.0, 0.5);
            if (value < 0) {
                tiles[x + y * width] = 6; //set water
            } else {
                tiles[x + y * width] = 1; //set grass
            }
        }
    }
}

There are also alternatives such as Perlin noise and Simplex noise. I'd skip Perlin noise entirely because it tends to exhibit visually significant grid artifacts (it lines all of its features up with its underlying square grid). Simplex noise in 2D is okay, though most implementations of 2D Simplex noise on the internet use a weird gradient set that results in artifacts down the negative diagonal. And 3D simplex noise is patent-saddled.

Perlin noise vs OpenSimplex noise, 2D slices of 3D:

• Left is noise(x, y, 0) grayscale
• Next is noise(x, y, 0) > 0 ? white : black
• Next is |noise(x, y, 0)| > 0.1 ? white : black
• Next is noise(x, y, 0.5) grayscale

EDIT: Here's the code from the comment

Fractal noise:

OpenSimplexNoise n1 = new OpenSimplexNoise(seed1);
OpenSimplexNoise n2 = new OpenSimplexNoise(seed2);
OpenSimplexNoise n3 = new OpenSimplexNoise(seed3);

for each x,y {
    double value = (n1.eval(x / 48.0, y / 48.0, 0.5) + n2.eval(x / 24.0, y / 24.0, 0.5) * .5 + n3.eval(x / 12.0, y / 12.0, 0.5) * .25) / (1 + .5 + .25);
    //Do whatever you need to with that value
}

Rivers:

if (value > -0.1 || value < 0.1)
    water
else
    land

Biomes:

OpenSimplexNoise n1 = new OpenSimplexNoise(seed1);
OpenSimplexNoise n2 = new OpenSimplexNoise(seed2);
OpenSimplexNoise n3 = new OpenSimplexNoise(seed3);

for each x,y {
    double elevation = n1.eval(x / 24.0, y / 24.0, 0.5);
    double temperature = n2.eval(x / 24.0, y / 24.0, 0.5);
    double precipitation = n3.eval(x / 24.0, y / 24.0, 0.5);

    if (elevation < 0)
        water
    else {
        //decide biome based on temperature, precipitation, and elevation
    }
}