Split Deck

Definable split-screen for Android "AI boxes" that project into a car's CarPlay window — built for, and tested on, a Carlinkit Ultra AI Box behind an XPeng G6.

The stock split feature on these boxes is a stub: it can only pin a shortcut, offers five fixed ratios, and silently does nothing unless the vendor's own launcher is the home screen. Split Deck replaces it with named splits, any pair of apps, a free ratio slider, and a pinned shortcut per split.

Install

Grab split-deck.apk from Releases, then:

adb install -r split-deck.apk
adb shell pm grant com.stevelea.splitdeck android.permission.WRITE_SECURE_SETTINGS   # lets it toggle freeform support

Open Split Deck, press + New split, pick the left and right app, drag the ratio, save. Launch runs it, Shortcut pins it to the home screen.

Two engines

	Stock split (default)	Freeform
what happens	writes persist.splitscreen.percent, then broadcasts com.android.intent.ext.main.split.two.screen	launches both apps as freeform windows at exact pixel bounds
needs	stock launcher as HOME, SELinux permissive	enable_freeform_support=1 (app toggles it)
looks	real system split, no title bars	freeform windows; title bars can appear if SystemUI starts with freeform enabled
survives app close	yes	yes (windows persist)

Uncheck "Use the box's stock split" per split to use the freeform path.

Ratio maths (this trips everyone up)

persist.splitscreen.percent is a ratio of the whole display panel, while the app can only measure its own window. On the tested box the panel is 2374 px and the app area 2270 px, so the same visible edge is:

	base	value
Stock split	2374 px panel	63:37 → divider at 1495 px
Freeform	2270 px app area	66% → 1498 px

Split Deck does that conversion for you: give it a percentage and it writes targetPx:(panelW − targetPx) to the property.

Launcher restrictions ⚠️

This is the part that makes the stock split look "broken" on these boxes.

1. The stock split only works when com.android.launcher3 is the default home. The broadcast com.android.intent.ext.main.split.two.screen has exactly one receiver — com.android.launcher3/.uioverrides.QuickstepLauncher, via SplitScreenManager.launchExistingSplitPair. If another launcher (Smart Launcher, Nova, …) is HOME, that activity never runs, the receiver is never registered, and the broadcast is dropped without an error.

   adb shell cmd package set-home-activity com.android.launcher3/.uioverrides.QuickstepLauncher
   adb shell setprop persist.vendor.launcher.select com.android.launcher3/.uioverrides.QuickstepLauncher

2. The launcher must be foreground when the broadcast lands. Split Deck therefore sends itself to the home screen and broadcasts ~1.9 s later.
3. Both apps need running tasks. The vendor manager resolves each package among running tasks; a force-stopped app makes the split silently not form. Split Deck launches both apps first, then goes home, then broadcasts.
4. The freeform engine has no launcher requirement — it positions windows itself — but needs enable_freeform_support=1. If SystemUI starts with that flag on it draws window title bars, so the app enables it for a launch and restores 0 afterwards.

Verified on

Device	Carlinkit Ultra AI Box ("lito for arm64", product sc162)
SoC	Qualcomm lito / SM6350
Android	15, build SC162-V06.000.002, vendor stack suding / speedplay
Display	2374×1016 @30 Hz, 238 dpi — app area 2270×1016 (vendor status strip ~104 px)
Car	XPeng G6 (model F30), XOS CarPlay card, projection area 2400×1016
SELinux	Permissive — required for the property write from an app
Root	adb shell is uid 0; no su for apps, and none needed

Verified by observation on the device (2026-11-02):

• stock split launched from Split Deck — both apps in one split root task, mode=multi, divider at exactly 1498 px;
• freeform split at 1498×981 with 10 px overscan, no clipping;
• pinned shortcut (dumpsys shortcut → Pinned: split-<uuid>) launches the split cold, after both apps were force-stopped;
• name editing saves on the keyboard's Enter/Done.

Not verified: any other box, firmware or car. Treat those rows as "designed for", not "tested on".

Requirements

• Android 8.0+ (minSdk 26), targetSdk 33; no root.
• WRITE_SECURE_SETTINGS via adb shell pm grant — only used to flip enable_freeform_support.
• For the stock engine: the vendor launcher as HOME and SELinux permissive (a system-signed build would not need that).

Known limitations

• A firmware update that sets SELinux to enforcing stops the app writing the property → stock engine breaks; switch splits to freeform.
• No boot-time auto-relaunch: splits are restored by tapping a shortcut.
• The stock engine depends on vendor internals (private broadcast, private property); they can change silently.
• Only one device is tested (see above).
• The editor is a dialog; on very short screens the keyboard can crowd it (Save & pin is left of Save).

Build

No Gradle. The app is four Java files and a manifest, built with the SDK command-line tools:

./build.sh          # needs ANDROID_SDK_ROOT (default ~/Library/Android/sdk) and a JDK 17+

Output: build/split-deck.apk. Signing uses a debug keystore generated on first build.

Layout

AndroidManifest.xml
src/com/stevelea/splitdeck/
  MainActivity.java   UI: list of splits, editor dialog, shortcuts
  Launcher.java       both engines: stock (property + broadcast) and freeform (bundle keys)
  Split.java          one saved split
  Store.java          JSON in SharedPreferences
  CalView.java        full-screen ruler used to measure the car's window
build.sh
docs/technical-notes.md

License

MIT — see LICENSE. Not affiliated with Carlinkit or XPeng. Use at your own risk: it writes a vendor system property and drives vendor internals.