Logic Island

Logic Island is my first homebrew game for the original Game Boy, yay!

• Download : https://tardigrade-nx.itch.io/logic-island

Logic Island a Picross-like logic puzzle game for the original Game Boy, inspired by Nikoli’s Nurikabe. Nurikabe is one of my favorite games of all times. This is my version of it, with graphics hopefully a little more elaborate than a simple grid.

The rules may not be as simple as Picross at first, but it’s worth it: once you know how to play, the game becomes very addictive, with a lot of depth and strategies to offer. I’ll try to explain as clearly as possible in this post, with a step-by-step tutorial below.

Rules

For example, here is an empty 5x5 grid, and the same grid, solved.

The objective is to draw a water stream, that fullfills all 4 conditions:

1. Each island has one numbered cell
2. This number is the number of cells in that island
3. There is only one stream in the perimeter (branches allowed)
4. There is no 2x2 squares of water

Additionally, you can mark cells with a stone when you’re sure it’s a ground cell. Stones are just an indication, they don’t count in the grid resolution.

Two cells touch if they’re adjacent, not diagonal.

Tutorial

As always with logic games, you should work by deduction, and not by guessing. Let’s take the example grid above.

• In accordance with rule #1, you can separate all the numbered cells.

• In accordance with rules #2, you can surround the [1] cells with water.

• In accordance with rules #3, each water cell must touch at least one other water cell in the perimeter. Thus, you can “extend” the isolated water cells when there’s only one path possible to do that. We could do this with the 4 cases here, but for the sake of the example, let’s do it only for the 2 upper cells.

• Now, following rule #2, there’s only one way that the [3] island in the upper-left corner can have 3 cells. We can mark those cells with stones (not mandatory), and “close” the island by surrounding it with water.

• Now if we look at the cell in the center: it cannot be water, otherwise that would create 2x2 squares of water, which is forbidden by rule #4. So we can be sure it’s a ground cell, and we can mark it with a stone. In general, as soon as there are 3 cells of water in a square formation, you can immediately mark the 4th with a stone.

• The only thing left to do is to connect the two isolated water cells to the rest of the water stream, according to rule #3, just like we did earlier.

And that’s it, the island is solved!

Techniques

There are many techniques you can use, resulting of the 4 rules above:

• Nurikabe techniques
• Nurikabe tutorial

RetroAchievements

I’ve made a set of RetroAchievements for the game. More info here.

Change log

v2.1

• The numbered tiles are greyed-out if the number of tiles is correct.

v2.0

• Added 10x10 grids.
• Display size and number when selecting grid.
• Updated to gbdk v4.2.0.

v1.1

• Fixed a glitch in Island #118, so that the correct answer is recognized properly.

v1.0

• Initial release

Credits

• Development: Tardigrade
• Original concept: Nurikabe, by Nikoli
• Title font: Grape Soda by jeti, licensed under CC BY 4.0
• Title graphics by GrafxKid, licensed under CC0 1.0
• Sound effects by Coffee ‘Valen’ Bat

The game was developed in C language, with gbdk.