# Debugging Tips

There are many ways to debug ANGLE using generic or platform-dependent tools. Here is a list of tips
on how to use them.

## Running ANGLE under apitrace on Linux

[Apitrace](http://apitrace.github.io/) captures traces of OpenGL commands for later analysis,
allowing us to see how ANGLE translates OpenGL ES commands. In order to capture the trace, it
inserts a driver shim using `LD_PRELOAD` that records the command and then forwards it to the OpenGL
driver.

The problem with ANGLE is that it exposes the same symbols as the OpenGL driver so apitrace captures
the entry point calls intended for ANGLE and reroutes them to the OpenGL driver. In order to avoid
this problem, use the following:

1. Link your application against the static ANGLE libraries (libGLESv2_static and libEGL_static) so
   they don't get shadowed by apitrace's shim.
2. Ask apitrace to explicitly load the driver instead of using a dlsym on the current module.
   Otherwise apitrace will use ANGLE's symbols as the OpenGL driver entrypoint (causing infinite
   recursion). To do this you must point an environment variable to your GL driver.  For example:
   `export TRACE_LIBGL=/usr/lib/libGL.so.1`. You can find your libGL with
   `ldconfig -p | grep libGL`.
3. Link ANGLE against libGL instead of dlsyming the symbols at runtime; otherwise ANGLE won't use
   the replaced driver entry points. This is done with the gn arg `angle_link_glx = true`.

If you follow these steps, apitrace will work correctly aside from a few minor bugs like not being
able to figure out what the default framebuffer size is if there is no glViewport command.

For example, to trace a run of `hello_triangle`, assuming the apitrace executables are in `$PATH`:

```
gn args out/Debug # add "angle_link_glx = true"
# edit samples/BUILD.gn and append "_static" to "angle_util", "libEGL", "libGLESv2"
ninja -C out/Debug
export TRACE_LIBGL="/usr/lib/libGL.so.1" # may require a different path
apitrace trace -o mytrace ./out/Debug/hello_triangle
qapitrace mytrace
```

## Running ANGLE under GAPID on Linux

[GAPID](https://github.com/google/gapid) can be used to capture trace of Vulkan commands on Linux.
For it to work, libvulkan has to be a shared library, instead of being statically linked into ANGLE,
which is the default behavior.  This is done with the gn arg:

```
angle_shared_libvulkan = true
```

When capturing traces of gtest based tests built inside Chromium checkout, make sure to run the
tests with `--single-process-tests` argument.

## Running ANGLE under GAPID on Android

[GAPID](https://github.com/google/gapid) can be used to capture a trace of the Vulkan or OpenGL ES
command stream on Android.  For it to work, ANGLE's libraries must have different names from the
system OpenGL libraries.  This is done with the gn arg:

```
angle_libs_suffix = "_ANGLE"
```

All
[NativeTest](https://chromium.googlesource.com/chromium/src/+/master/testing/android/native_test/java/src/org/chromium/native_test/NativeTest.java)
based tests share the same activity name, `org.chromium.native_test.NativeUnitTestNativeActivity`.
Thus, prior to capturing your test trace, the specific test APK must be installed on the device.
When you build the test, a test launcher is generated, for example,
`./out/Release/bin/run_angle_end2end_tests`. The best way to install the APK is to run this test
launcher once.

In GAPID's "Capture Trace" dialog, "Package / Action:" should be:

```
android.intent.action.MAIN:org.chromium.native_test/org.chromium.native_test.NativeUnitTestNativeActivity
```

The mandatory [extra intent
argument](https://developer.android.com/studio/command-line/adb.html#IntentSpec) for starting the
activity is `org.chromium.native_test.NativeTest.StdoutFile`. Without it the test APK crashes. Test
filters can be specified via either the `org.chromium.native_test.NativeTest.CommandLineFlags` or
the `org.chromium.native_test.NativeTest.Shard` argument.  Example "Intent Arguments:" values in
GAPID's "Capture Trace" dialog:

```
-e org.chromium.native_test.NativeTest.StdoutFile /sdcard/chromium_tests_root/out.txt -e org.chromium.native_test.NativeTest.CommandLineFlags "--gtest_filter=*ES2_VULKAN"
```

or

```
-e org.chromium.native_test.NativeTest.StdoutFile /sdcard/chromium_tests_root/out.txt --esal org.chromium.native_test.NativeTest.Shard RendererTest.SimpleOperation/ES2_VULKAN,SimpleOperationTest.DrawWithTexture/ES2_VULKAN
```

## Running ANGLE under RenderDoc

An application running through ANGLE can confuse [RenderDoc](https://github.com/baldurk/renderdoc),
as RenderDoc [hooks to EGL](https://github.com/baldurk/renderdoc/issues/1045) and ends up tracing
the calls the application makes, instead of the calls ANGLE makes to its backend.  As ANGLE is a
special case, there's little support for it by RenderDoc, though there are workarounds.

### Windows

On Windows, RenderDoc supports setting the environment variable `RENDERDOC_HOOK_EGL` to 0 to avoid
this issue.

### Linux

On Linux, there is no supported workaround by RenderDoc.  See [this
issue](https://github.com/baldurk/renderdoc/issues/1045#issuecomment-463999869).  To capture Vulkan
traces, the workaround is to build RenderDoc without GL(ES) support.

Building RenderDoc is straightforward.  However, here are a few instructions to keep in mind.

```
# Install dependencies based on RenderDoc document.  Here are some packages that are unlikely to be already installed:
$ sudo apt install libxcb-keysyms1-dev python3-dev qt5-qmake libqt5svg5-dev libqt5x11extras5-dev

# Inside the RenderDoc directory:
$ cmake -DCMAKE_BUILD_TYPE=Release -Bbuild -H. -DENABLE_GLES=OFF -DENABLE_GL=OFF

# QT_SELECT=5 is necessary if your distribution doesn't default to Qt5
$ QT_SELECT=5 make -j -C build

# Run RenderDoc from the build directory:
$ ./build/bin/qrenderdoc
```

Additionally, libvulkan has to be a shared library, instead of being statically linked into ANGLE,
which is the default behavior.  This is done with the gn arg:

```
angle_shared_libvulkan = true
```

If your distribution does not provide a recent Vulkan SDK package, you would need to manually
install that.  This script tries to perform this installation as safely as possible.  It would
overwrite the system package's files, so follow at your own risk.  Place this script just above the
extracted SDK directory.

```
#! /bin/bash

if [ $# -lt 1 ]; then
  echo "Usage: $0 <version>"
  exit 1
fi

ver=$1

if [ ! -d "$ver" ]; then
  echo "$ver is not a directory"
fi

# Verify everything first
echo "Verifying files..."
echo "$ver"/x86_64/bin/vulkaninfo
test -f "$ver"/x86_64/bin/vulkaninfo || exit 1
echo "$ver"/x86_64/etc/explicit_layer.d/
test -d "$ver"/x86_64/etc/explicit_layer.d || exit 1
echo "$ver"/x86_64/lib/
test -d "$ver"/x86_64/lib || exit 1

echo "Verified. Performing copy..."

echo sudo cp "$ver"/x86_64/bin/vulkaninfo /usr/bin/vulkaninfo
sudo cp "$ver"/x86_64/bin/vulkaninfo /usr/bin/vulkaninfo
echo sudo cp "$ver"/x86_64/etc/explicit_layer.d/* /etc/explicit_layer.d/
sudo cp "$ver"/x86_64/etc/explicit_layer.d/* /etc/explicit_layer.d/
echo sudo rm /usr/lib/x86_64-linux-gnu/libvulkan.so*
sudo rm /usr/lib/x86_64-linux-gnu/libvulkan.so*
echo sudo cp -P "$ver"/x86_64/lib/lib* /usr/lib/x86_64-linux-gnu/
sudo cp -P "$ver"/x86_64/lib/lib* /usr/lib/x86_64-linux-gnu/

echo "Done."
```
