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docs/debugging: Expand on Renderdoc and built-in support

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Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/4061>
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Sebastian Wick 2024-10-02 18:33:46 +02:00 committed by Marge Bot
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doc/debugging.md
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@ -62,7 +62,12 @@ Debugging GL based applications can be hard without insights into the GL state t
For more detailed state dumps, it's possible to use graphics debuggers such as apitrace and renderdoc.
Renderdoc is usually the better tool to debug something with, but it's also harder to capture a trace. In those cases apitrace can help by capturing trace by wrapping the Mutter invocation with `apitrace trace --api=egl` and then capturing with renderdoc the replay of the apitrace (`eglretrace mutter.trace`).
Mutter has built-in Renderdoc support (see `meta_backend_renderdoc_capture` and lg `global.context.get_backend().renderdoc_capture()`).
To get renderdoc to capture mutter, `LD_PRELOAD` must be set to the path of `librenderdoc.so`. If any process is in between setting the environment variable and mutter, it will fail.
For example, `LD_PRELOAD=path/to/librenderdoc.so dbus-run-session gnome-shell --wayland` will not work, but `dbus-run-session env LD_PRELOAD=path/to/librenderdoc.so gnome-shell --wayland` will.
The way gdb starts the target also involves another process, so use `gdb -ex 'set exec-wrapper env LD_PRELOAD=path/to/librenderdoc.so'` in those cases.
Apitraces can help by capturing multiple frames. The mutter invocation can be wrapped with `apitrace trace --api=egl` to capture a trace which can be replay with `eglretrace`. Apitrace can also be captured by renderdoc to select a single frame to investigate further.
## Reproducing CI test failures locally