mobilegl-dev/mobilegl/trace-fixture-authoring-on-android-fcl

MobileGL Android trace capture

Overview

Use FCL's Android egltrace.so wrapper, not Perfetto. When enabled before launch, it records the complete EGL/GL call stream to full.trace. The game's MobileGL Trace → Capture control marks the next swap frame in capture-result.json; it does not start or stop recording and does not produce a one-frame trace by itself.

Run commands from the FoldCraftLauncher repository root:

export REPO="$PWD"
export CAPTURE="$REPO/MobileGL/tools/trace_replay/skills/trace-fixture-authoring-on-android-fcl/scripts"
export SERIAL=<adb-device-serial> # omit --serial only if exactly one device is attached

The capture scripts are bundled inside this skill under scripts/; they auto-detect the FoldCraftLauncher repository root from their own location, so --repo only needs to be passed for a non-standard checkout layout.

Prerequisites

• Use an FCL build containing MobileGLTraceCapture and the in-game Capture

menu entry.

• Select one of these renderers: MobileGL (DirectGLES), MobileGL Magma

(DirectVulkan), or SimpleFPEWrapper. MobileGlues is not supported by this capture wrapper.

• Install adb and make it available on PATH; authorize USB debugging.
• Build the wrapper with Android NDK, CMake, Ninja, Python 3, and the checked

out in-tree MobileGL/3rdparty/apitrace submodule.

Confirm the attached device and ABI before building. The wrapper ABI must match the device process ABI.

adb devices -l
adb -s "$SERIAL" shell getprop ro.product.cpu.abi

Use arm64-v8a for the usual arm64-v8a result; use the matching NDK ABI for other devices.

Build and install the wrapper

Build once per ABI or after changing apitrace/wrapper sources:

python3 "$CAPTURE/build_android_egltrace.py" --abi arm64-v8a

This generates egltrace.so under the skill's scripts/out/ directory. Push it and write FCL's enable sentinel before launching the game:

python3 "$CAPTURE/adb_capture.py" --serial "$SERIAL" install-wrapper
python3 "$CAPTURE/adb_capture.py" --serial "$SERIAL" enable

The device-side control directory is /sdcard/FCL/mobilegl-trace. FCL copies the shared egltrace.so into its private files directory at launch, replaces the renderer's EGL library with it, and forwards to the real MobileGL library.

Capture a reproduction

1. Start FCL after the wrapper and enable sentinel are in place. Select the

intended supported MobileGL renderer and launch the game.

1. Trace mode forces the game to 854x480; account for that when reproducing

and comparing output.

1. Reproduce the issue. Start close to the target scene because tracing starts

when the game launches and trace files can grow rapidly.

1. At the desired visual state, open FCL's right-side game menu and press

MobileGL Trace → Capture. Let at least one frame present afterward.

1. Exit the game cleanly, then pull the latest session:

python3 "$CAPTURE/adb_capture.py" --serial "$SERIAL" pull-latest

The default local result is:

.trace-work/pulled-mobilegl-captures/capture-YYYYMMDD-HHMMSS-<renderer>/
  full.trace
  capture-status.json
  capture-result.json

capture-result.json must show "status": "captured". Its targetFrame is the one-based swap count used by gltrim; zeroBasedFrame is included for tools that use zero-based indexing.

Diagnose setup failures

Inspect the active device session directly:

adb -s "$SERIAL" shell cat /sdcard/FCL/mobilegl-trace/latest-session.txt
adb -s "$SERIAL" shell ls -lh /sdcard/FCL/mobilegl-trace
adb -s "$SERIAL" shell cat /sdcard/FCL/mobilegl-trace/capture-*/capture-status.json
adb -s "$SERIAL" shell cat /sdcard/FCL/mobilegl-trace/capture-*/capture-result.json

If capture-status.json reports a missing egltrace.so, rebuild/push the correct ABI and relaunch. If capture-result.json is absent, Capture was pressed without an active trace session, or no subsequent eglSwapBuffers occurred. The menu button itself only writes capture-once.request.

Disable tracing when finished; otherwise the next supported MobileGL launch will trace again:

python3 "$CAPTURE/adb_capture.py" --serial "$SERIAL" disable

Create a replay fixture (optional)

Keep the raw full.trace until replay validation succeeds. To frame-trim and package the marked frame for MobileGL trace replay, use the existing helper:

python3 "$CAPTURE/package_capture_fixture.py" \
  --serial "$SERIAL" \
  --case <case-name> \
  --apitrace <path-to-in-tree-apitrace>

It pulls the latest capture if necessary, uses capture-result.json to select the frame, runs apitrace gltrim, creates a golden image, and enforces the fixture archive-size limit. Follow ../trace-fixture-authoring/SKILL.md for deterministic scene setup, verification, and registry changes.