See the demo

npm install block-fractal

Create a block fractal:

const BlockFractal = require('block-fractal');

const path = BlockFractal.makeBlockFractal({
    iterations: 7
});

Convert the path into a set of raster lines (makes cell tests faster):

const mask = path.rasterize();

Test if a tile is in the shape:

const inside = mask.get(x, y);

...

BlockFractal starts with a "seed" shape, which by default is a 2x2 square:

The shape is doubled, and then each edge is either left in place or moved to one side or the other:

The result is a new, bigger shape, similar to the previous shape but with a more varied border:

That process is then repeated as many times as requested.

For more information, see the Algorithm Overview