How to Generate Realistic Islands Using a Modified Diamond-Square Algorithm?

Perlin Noise Islands with No Circles

Instead of using gradient circles, consider utilizing Diamond & Square algorithm with some modifications to create natural-looking islands within your map generator.

Diamond & Square Algorithm with Modifications

• Configure generation properties: Establish parameters like maximum and minimum elevations, sea level, and vegetation ranges.

• Create terrain height map (zed[][]):

  • Modify the Diamond & Square algorithm to avoid "inland" terrains by initializing corners with the lowest elevation.
  • Ignore the first diamond step and initialize the midpoint with a random value.
  • After each square iteration, adjust border points to the minimum (underwater) elevation.

• Create surface map (typ[][]):

  • Assign surface features based on elevation, like water, sand, vegetation, and rock.
  • Add features based on terrain slope, such as rocks.
  • Include additional elements like rivers, streams, and buildings based on specific rules.

Example C Implementation

void map_random(int _xs, int _ys) {
  // Configuration and parameter initialization

  // Terrain generation
  ter=new int*[mys+1]; for (y=0;y<=mys;y++) ter[y]=new int[mxs+1];
  typ=new int*[mys+1]; for (y=0;y<=mys;y++) typ[y]=new int[mxs+1];
  ...

  // First pass
  t=-r2;
  ter[  0][  0]=t;
  ter[  0][mxs]=t;
  ter[mys][  0]=t;
  ter[mys][mxs]=t;
  ter[dy2][dx2]=r2;

  ...

  for (;dx2|dy2;dx=dx2,dx2>>=1,dy=dy2,dy2>>=1)    // subdivide step until full image is filled
  {
    ...
    // diamond (skip first one for islands)
    if ((!_island)||(dx!=mxs))
     for (y=dy2,yy=mys-dy2;y<=yy;y+=dy)
      for (x=dx2,xx=mxs-dx2;x<=xx;x+=dx)
       ter[y][x]=((ter[y-dy2][x-dx2]+ter[y-dy2][x+dx2]+ter[y+dy2][x-dx2]+ter[y+dy2][x+dx2])>>2)+Random(r)-r2;
    ...
    // adjust border
    if (_island)
        {
        for (y=0;y<=mys;y+=dy2) { ter[y][0]=t; ter[y][mxs]=t; }
        for (x=0;x<=mxs;x+=dx2) { ter[0][x]=t; ter[mys][x]=t; }
        }
  }

  // Additional steps and enhancements
  ...
}

Output

This approach produces more natural-looking islands with multiple hills and realistic coastlines.

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