bangfireball--Phonecast_VR/docs/development.md

Development

Receiver prerequisites

• Git
• CMake 3.24 or newer
• Ninja
• A C++17 compiler
• SteamVR for receiver runtime testing

CMake fetches the OpenVR 2.15.6 source pinned at commit 0924064316de3effbcd1acf1e309182a2deb1c05.

Windows x64 receiver

cmake --preset windows-x64
cmake --build --preset windows-x64
ctest --test-dir out/build/windows-x64 --output-on-failure

Run SteamVR, then:

.\out\build\windows-x64\bin\phonecast-receiver.exe --duration-seconds 10

The build places openvr_api.dll and phonecast-receiver.vrmanifest beside the executable.

Sprint 3 desktop streaming receiver:

.\out\build\windows-x64\bin\phonecast-stream-receiver.exe --pair-code 123456

Sprint 4 OpenVR streaming receiver (start SteamVR first):

.\out\build\windows-x64\bin\phonecast-vr-stream-receiver.exe --pair-code 123456

The VR receiver uses global controls while Ctrl+Alt is held: P toggles visibility, +/- changes scale, arrows move, Page Up/Down changes distance, ]/[ changes opacity, H/W selects head/world lock, L/R selects left/right-controller lock, Home resets, and End quits. Point a SteamVR controller laser at the overlay and hold trigger to grab it directly; releasing creates a world-locked anchor at that pose.

Overlay appearance and placement are saved by default to %LOCALAPPDATA%\PhoneCastVR\overlay-settings.ini. Use --settings PATH to select a different file. Selecting world lock snapshots the panel's current position into standing space. Selecting a controller requires that role to be available; an unavailable controller leaves the previous placement active. Sprint 5's placement behavior was physically approved over a PC SteamVR game on 2026-10-02. Controller ergonomics remain Sprint 5.1 polish.

The Windows receiver's overlay disappears when the user switches to a headset-native standalone game. That game is rendered by the headset's native compositor rather than the PC SteamVR compositor hosting this process, so this is expected for the current backend and does not block the PC-hosted Sprint 5 milestone. Native coexistence with a standalone VR scene still requires the Steam Frame ARM64 backend and validation tracked for Sprint 11.

The Android sender connects to the PC's LAN IPv4 address on TCP port 49321. Windows Firewall must permit inbound private-network TCP traffic for the receiver. The pairing code must contain exactly six digits. The current protocol is not encrypted; use only a trusted development LAN.

Important: do not start SteamVR through Windows RDP

A physical Steam Frame/VRLink test on 2026-10-02 showed that starting or restarting SteamVR from an active Remote Desktop session can break all streamed PC content, not only PhoneCast. Symptoms included a gray headset view, invisible raw and D3D11 overlays, games failing to appear, repeated VRLink Failed to create d3d11textures messages, and compositor WaitForAcquire timed out warnings.

Closing the RDP window is insufficient if Steam or SteamVR remains in the disconnected RDP session. Before testing:

1. run Steam and SteamVR in the physical Windows console session;
2. verify query session reports the development user on console rather than rdp-tcp;
3. reconnect or sleep/wake the Frame after correcting the Windows session;
4. confirm an ordinary PC game streams before diagnosing PhoneCast.

If the failure recurs, stop SteamVR, transfer/log into the physical console session, relaunch SteamVR there, reconnect or sleep/wake the Frame, and confirm ordinary game streaming first. Do not interpret overlay results obtained during the broken RDP/VRLink state as application results.

The 2026-10-02 physical Sprint 4 test subsequently confirmed a visible Android screen in the headset. On the multi-GPU host, OpenVR D3D11 overlays were invisible until the renderer used the adapter returned by GetDXGIOutputInfo; updates advanced only about once per five seconds until the D3D11 context was explicitly flushed. The corrected generated animation was visually smooth before the phone stream was retested successfully.

Current physical-test result: after enabling Media Foundation low-latency mode, the user reported near-instant initial appearance and touch-to-display response under one second, including isolated changes on static content; YouTube playback was watchable and the result was explicitly approved. These timings are user estimates rather than instrumented measurements. Landscape still fails while portrait works. The prior right-edge green bar is fixed. Persistence over a running VR game and the PC keyboard overlay controls are confirmed. Sprint 4 keyboard shortcuts adjust only the overlay; headset-native placement and interaction with Android are not implemented. Phone audio remains on the phone because audio transport is outside the visual MVP.

OpenVR's VREvent_ProcessQuit may refer to an unrelated scene application. It must not terminate the receiver; only explicit runtime/driver quit events should do so. Treating it as a shutdown request caused the overlay process to exit during the first VR-game transition test.

Useful overlay receiver options:

--width N
--height N
--fps N
--overlay-width M
--distance M
--alpha A
--duration-seconds N

Use --help for ranges and defaults.

Sparse-update latency regression (2026-10-02)

The Windows decoder now enables low-latency mode before configuring its media types. Previously, its internal buffering could hold a screen update until more frames arrived, despite millisecond decode times and an empty TCP receive queue. See Microsoft's H.264 decoder attributes and low-latency property.

phonecast-mf-sparse-frame-latency tests an IDR and two P-frames with no future input or EOS drain allowed before each picture appears. It fails before the fix and passes afterward on the Windows development host. It needs Media Foundation, not SteamVR, a phone, or FFmpeg. Fixture generation is documented in tests/fixtures/README.md.

A full build and all nine tests passed in out/build/windows-x64-latency while the old VR receiver remained running. To physically retest, exit the old receiver (Ctrl+Alt+End), then run from the console session:

.\out\build\windows-x64-latency\bin\phonecast-vr-stream-receiver.exe --pair-code 123456

No sender reinstall is required. Compare an isolated phone tap followed by no motion, continuous scrolling, and startup; use the desktop receiver separately for comparison. After restarting the fixed receiver, the user physically retested and reported “this is perfect. very snappy.” A follow-up covered startup, isolated updates on static content, and sustained dynamic content: startup was described as near-instant, touch-to-display as under one second and near-instant, and YouTube as watchable. The user explicitly approved the result. End-to-end responsiveness is qualitatively confirmed; quantitative latency and startup timings remain unmeasured. Sparse rx-fps=0 on a static screen is not alone evidence of capture failure.

Linux ARM64 receiver cross-build

Install an AArch64 GNU compiler, then configure with the checked-in toolchain:

cmake -S . -B out/build/linux-arm64 \
  -G Ninja \
  -DCMAKE_BUILD_TYPE=Release \
  -DCMAKE_TOOLCHAIN_FILE=cmake/toolchains/linux-arm64-gcc.cmake
cmake --build out/build/linux-arm64
file out/build/linux-arm64/bin/phonecast-receiver

The result should identify as an AArch64 ELF. Deploy the executable and adjacent manifest with Steam Linux Runtime 3.0 ARM64 (Sniper). See docs/steam-frame.md for established Steam Frame deployment findings.

Android sender

Requirements:

• Android SDK 36
• JDK 17 or newer
• An Android 10+ device for runtime validation

The sender includes a Gradle wrapper. From the repository root:

cd android\sender
.\gradlew.bat testDebugUnitTest assembleDebug lintDebug

Install the debug APK on a connected device:

adb install -r app\build\outputs\apk\debug\app-debug.apk
adb logcat -s PhoneCastCapture

See android/sender/README.md and docs/android-capture.md for behavior and permission requirements.

CMake options

• PHONECAST_BUILD_RECEIVER — build the generated OpenVR receiver and, on Windows, the desktop and OpenVR stream receivers (default ON).
• PHONECAST_BUILD_HELLO_FRAME — retain the Sprint 0 experiment (default ON).
• BUILD_TESTING — build/register tests (default controlled by CTest, normally ON).

Tests

Receiver unit tests use fake logging and overlay implementations, so they do not require SteamVR. Android configuration tests also run without a device. Neither suite replaces visual compositor checks or physical-device capture/encoder tests.