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#cat #ebitengine #go #golang #neko #retro

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README

Neko

Neko) is a cat that chases the mouse cursor across the screen, an app written in the late 1980s and ported for many platforms.

Neco

This code is a re-implementation using Golang and has no relationship to the original software. Furthermore, this version does not use any part of the original source code except sprites and sounds.

The goal is to demonstrate the Go language with a fun and very nostalgic example, without necessarily being tied to the behavior of the original version.

In this example, we used the Ebitengine, an incredibly easy-to-use gaming library with a vibrant community.

Download (no Go required)

If you just want to use Neko, download a prebuilt binary from the latest release. You do not need Go or any developer tools.

Pick the file for your system:

| System | File to download | | --- | --- | | macOS (Intel or Apple Silicon) | neko-darwin-universal.zip | | Windows (64-bit, most common) | neko-windows-amd64.exe | | Windows (older 32-bit) | neko-windows-386.exe | | Windows (ARM) | neko-windows-arm64.exe | | Linux (Intel/AMD 64-bit) | neko-linux-amd64.gz | | Linux (ARM 64-bit) | neko-linux-arm64.gz |

macOS

Download neko-darwin-universal.zip and double-click it to unzip. You will get neko.app.
Move neko.app to your Applications folder (recommended).
Double-click neko.app to run it.

The app is signed and notarized by Apple, so it should open normally. The single "universal" build works on both Intel and Apple Silicon Macs, so there is no need to choose an architecture.

If macOS shows "neko.app is damaged and can't be opened" or warns about an unidentified developer:

Make sure the download finished completely, and unzip the file before opening

it (do not run the app from inside the .zip). Re-download if in doubt.

Right-click (or Control-click) neko.app, choose Open, then confirm with

Open in the dialog.

If it still will not open, open the Terminal app and run (adjust the path

if you did not move it to Applications):

xattr -dr com.apple.quarantine /Applications/neko.app

Check System Settings → Privacy & Security → Security and make sure

"Allow applications downloaded from" is set to App Store & Known Developers, not App Store only.

Windows

Download the .exe for your system and double-click it. Windows SmartScreen may warn you because the app is not from the Microsoft Store: click More info → Run anyway to start it.

Linux

Download the matching .gz, then decompress and run it:

gunzip neko-linux-amd64.gz
chmod +x neko-linux-amd64
./neko-linux-amd64

Run from source

If you have Go installed and want to run Neko from source:

go run main.go

Or build the binary and run it:

go build -o neko main.go

On macOS and Windows no extra dependencies are needed. On Linux, Ebitengine requires Cgo and the system development libraries, so build with CGO_ENABLED=1 after installing the packages listed in the Ebitengine install guide (for example, on Debian/Ubuntu: libgl1-mesa-dev, libasound2-dev, libxcursor-dev, libxi-dev, libxinerama-dev, libxrandr-dev, libxxf86vm-dev, and pkg-config).

Configuration

Neko is configured with a Filo script. On startup it looks for the config file in this order:

./neko_init.filo in the current directory.
$XDGCONFIGHOME/neko/init.filo (defaults to ~/.config/neko/init.filo).

If no file is found, the built-in defaults are used. Any setting omitted from the file keeps its default. See neko_init-sample.filo for a starting point:

(do
  (set Speed 2.0)             ;; movement speed of the cat
  (set Scale 2.0)             ;; on-screen scale of the cat
  (set Quiet #f)              ;; #t disables sound
  (set MousePassthrough #f)   ;; #t lets clicks pass through the window
  (set SpriteSheet ""))       ;; path to a custom sprite sheet; empty uses the built-in cat

Settings:

Speed The speed of the cat (default 2.0).
Scale The scale of the cat on the screen (default 2.0).
Quiet Disable sound (default #f).
MousePassthrough Enable mouse passthrough (default #f).
SpriteSheet Path to a custom sprite sheet (default empty; see Sprite sheets and skins).

Command-line flags

Flags override the config file (precedence: defaults < config file < flags):

-speed The speed of the cat (default 2.0).
-scale The scale of the cat on the screen (default 2.0).
-quiet Disable sound.
-mousepassthrough Enable mouse passthrough.
-spritesheet Path to a custom oneko-layout sprite sheet (PNG).
-h Show help.

Sprite sheets and skins

Neko draws its frames from a single sprite sheet: an 8x4 grid of 32x32 tiles (256x128). The tile layout follows adryd325/oneko.js, so sprite sheets from the oneko ecosystem can be loaded as skins.

Pass your own sheet with -spritesheet path/to/sheet.png (or the SpriteSheet config setting). When no sheet is given, the built-in cat is used.

The built-in sheet (assets/neko.png) is generated from the individual sprite files in sprites/. To regenerate it after editing those sprites:

GENSHEET=1 go test -run TestGenerateSpriteSheet

How to install

Before installing Neko, make sure you have Go installed on your system, as we will be using go install.

Install dependencies, build, and install the project into your Go bin directory:

cd neko
go mod tidy
go install

To use Neko globally across your system, check if your Go bin directory is in your $PATH by running:

echo $PATH

If you don't see a Go bin directory, you'll need to add the following line to your ~/.bashrc, ~/.zshrc, or the equivalent shell configuration file:

export PATH=$PATH:$(go env GOPATH)/bin

After that, you can simply run neko in your terminal. If you want it to start with your system, you can add it to your .xinitrc or a similar startup script.