Sharing physics code between Desktop and Android — recommended / supported approach?

[bolotov]

Summary / Problem

When targeting both Desktop and Android, it is currently easy to accidentally structure a project in a way that causes desktop physics code or bytecode to be pulled into Android builds, leading to runtime failures on Android.

In particular, placing physics setup code (e.g. creating PhysicsWorld, Material, RigidDynamic, etc.) into a shared JVM or KMP module can result in the shared code being compiled against the desktop JVM variant of kool-physics. This embeds desktop-specific bytecode into the shared module, which then fails to load on Android at runtime.

From a user perspective, this is not obvious and can happen naturally when trying to reduce duplication and share scene/physics logic.

---

Observations

• Kool provides separate Desktop and Android physics artifacts with the same public API but different compiled bytecode.
• A shared JVM module must resolve one concrete variant at compile time, which defaults to the desktop one .
• As a result, shared physics code may unintentionally depend on desktop-only classes, even if Android dependencies are declared correctly.
• Kool examples seem to avoid this implicitly by keeping physics construction platform-specific or desktop-only, but this constraint is not explicitly documented.

---

Question / Request for guidance

What is the intended or recommended way to structure physics code when supporting both Desktop and Android?

In particular:

• What is the best way to share physics code, android / desktop sharing.
• Are there supported or preferred patterns for sharing physics-related logic safely (e.g. facades, backends, expect/actual, etc.)?
• Minimal docs...

Even brief guidance on how you envision this being handled would help avoid accidental misconfiguration and runtime issues.

---

Thanks for your work on Kool and for any advice you can provide.

[bolotov]

There is an android demo/example but it contains a teapot + hdri and has no physics in it

[fabmax]

That's a good point. Physics support on Android is quite new and so far I haven't tried it in multiplatform projects. Actually I was expecting that it would just work...

I did test physics in an Android only project and there it worked. To do so it should be enough to add kool-physics to the dependencies (I did use the kool-android-template project for that you are referring to).

For multiplatform I can't really give you much advice at the moment unfortunately...