It's not a trade secret, once I've got the basics of the roguelike working I'll be posting it up here :^)
Short answer: in the screenshots above the red is the floor, the white is the walls and the blue is the solid rock the dungeon is carved out of. The thin white lines are what your @ can walk along.
Long answer: Most roguelikes take place on a grid with either 8-way or 4-way movement. There's also some 6-way hexgrid based ones and even a
crazy hyperbolic plane roguelike.
I thought it would be cool to be able to do n-way movement, though I've limited it to a max of 8-way so that the usual roguelike movement controls work (hjklyubn and numpad keys). The easiest solution I could think of was a 2D graph where the points are 'tiles' and the edges between them are routes you can travel. The test data in the metalines demo, the lines in the screenshots above, are a generated level from the very early stages of coding the roguelike.
While playing around with level generation it became obvious that just looking at points and lines is a bit boring. A little green circle isn't as good as a grass tile, a bunch of blue lines doesn't look like a lake, even ASCII based roguelikes look prettier. So I needed to draw walls and floors somehow.
I had two choices either do something mesh based like
Voronoi diagrams or something pixel based like metaballs/metalines. The voronoi based solution requires creating lots of extra points around the level to make the walls of the dungeon work correctly which is a pain to do well. So I started playing around with efficiently rendering metalines instead and wrote the demo in the above post.