[Test] (CTS): run VK-GL-CTS KHR-GL33 against MobileGL on Android via a standalone glcts binary

tools/cts/README.md

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+# Running the OpenGL CTS (VK-GL-CTS / KHR-GL33) against MobileGL on Android
+
+Goal: measure how much of the OpenGL 3.3 core-profile conformance suite MobileGL
+passes, separately for each backend (`DirectGLES`, `DirectVulkan`).
+
+## How MobileGL is reached from a test binary
+
+MobileGL ships its own EGL implementation alongside its desktop-GL implementation
+in a single `libMobileGL.so`. A plain arm64 ELF in `/data/local/tmp` can therefore
+drive it with no APK and no Activity:
+
+1. `setenv("MOBILEGL_BACKEND_TYPE", "DirectGLES"|"DirectVulkan")` **before** the
+   library is mapped — MobileGL parses its configuration from an ELF constructor.
+2. `dlopen("libMobileGL.so")`, then `dlsym` the `egl*` and `gl*` entry points.
+   MobileGL exports 45 EGL symbols and the desktop GL functions directly;
+   `eglGetProcAddress` resolves the same set.
+3. `eglBindAPI(EGL_OPENGL_API)`, choose a config with `EGL_RENDERABLE_TYPE =
+   EGL_OPENGL_BIT`, then `eglCreateContext` with
+   `EGL_CONTEXT_OPENGL_PROFILE_MASK = EGL_CONTEXT_OPENGL_CORE_PROFILE_BIT` and
+   major/minor `3`/`3`.
+
+This yields a genuine GL 3.3 core context (`GL_CONTEXT_PROFILE_MASK == 0x1`).
+
+## Surface type, per backend
+
+| backend | pbuffer (headless) | window |
+|---|---|---|
+| `DirectGLES` | works | works |
+| `DirectVulkan` | **unusable** | works |
+
+`DirectVulkan`'s pbuffer path builds a headless `VkSurfaceKHR` and so requires the
+`VK_EXT_headless_surface` instance extension, which Adreno's Android driver does
+not expose. It fails inside `eglMakeCurrent`, not at surface creation.
+
+The workaround that keeps everything in a shell process: obtain a real
+`ANativeWindow` from **`AImageReader`** (`AImageReader_newWithUsage` +
+`AImageReader_getWindow`). It is an ordinary BufferQueue producer, so
+`vkCreateAndroidSurfaceKHR` accepts it, and no Activity is involved. Register an
+`onImageAvailable` listener that acquires and deletes each image — otherwise the
+producer blocks once `maxImages` buffers are in flight and the next swap hangs.
+
+## Why the suite must render into an FBO
+
+On a window surface, `DirectVulkan`'s `glReadPixels` from the **default
+framebuffer** returns all zeros, with no GL error, both before and after
+`eglSwapBuffers`. `DirectGLES` on the identical window is correct, and readback
+from a **user FBO is correct on both backends**.
+
+Verified on two SoCs and two drivers, so this is MobileGL's behaviour rather than
+a driver quirk:
+
+| device | GPU | driver | default-FB | user FBO |
+|---|---|---|---|---|
+| Xiaomi 24129PN74C | Adreno 830 | Vulkan 1.3.284 / 512.800.46 | zeros | ok |
+| Lenovo TB321FU | Adreno 750 | Vulkan 1.3.128 / 512.762.28 | zeros | ok |
+
+dEQP verifies nearly every case through `glReadPixels`, so running it against the
+default framebuffer would score `DirectVulkan` near zero for a reason unrelated to
+conformance. The runs therefore use `--deqp-surface-type=fbo`, uniformly for both
+backends so the two numbers stay comparable.
+
+## Other constraints the harness must respect
+
+- `eglMakeCurrent` requires **draw == read** and rejects `EGL_NO_SURFACE` with
+  `EGL_BAD_MATCH`. dEQP's `surfaceless` platform is therefore unusable, which is
+  why this port supplies its own `tcu::Platform`.
+- MobileGL aborts during static teardown (`FORTIFY: pthread_mutex_lock called on a
+  destroyed mutex`) *after* all work completes. Flush and `_exit()` so the exit
+  code and the `.qpa` log survive.
+
+## Contents
+
+    probe/mgprobe.c        preflight gate: one backend x one surface type, checks
+                           context version/profile and both readback paths
+    scripts/qpa_report.py  .qpa -> pass rate, status histogram, worst groups
+
+### Preflight
+
+    aarch64-linux-android26-clang -O1 -o mgprobe mgprobe.c -ldl -llog -landroid -lmediandk
+    adb push mgprobe libMobileGL.so /data/local/tmp/mgcts/
+    adb shell 'cd /data/local/tmp/mgcts && LD_LIBRARY_PATH=. ./mgprobe \
+        --backend DirectVulkan --surface imagereader --lib ./libMobileGL.so'
+
+Exit status is 0 when a 3.3 core context came up and FBO readback is correct.
+Default-framebuffer readback is reported but deliberately does not gate.