King under the Mountain was developed by Rocket Jump Technology, and has now been released as open-source under the very permissive MIT license.
This game is written in Java (currently version 17) using LibGDX
LibGDX uses Gradle as a build tool, so you'll need to run gradlew build at least once (though not for general development).
The core module contains the main game code and assets, the desktop module is the desktop launcher and platform-specific binaries.
The source contains two classes with runnable main methods, DesktopLauncher and RunTexturePacker.
Both of these classes expect to be run where the assets directory exists, i.e. they need to be run with ./core as the working directory.
RunTexturePacker reads the source asset files in (from current working directory) ./mods/base and packages them into ./assets.
This process has already been run and this repository contains the output files, it only needs to be re-run when there is a change to asset files.
DesktopLauncher is the game launcher. Run this with ./core as the working directory.
To package for release, you need to download AdoptOpen JDK releases from https://adoptopenjdk.net/releases.html for the packing process (packr.jar) to use. You will likely need to change the packr config files from OpenJDK17U-jdk_x64_windows_hotspot_17.0.2_8 to whatever version you have downloaded.