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Debugging the engine

Gary Qian edited this page Jan 17, 2019 · 5 revisions

This page has some hints about debugging the engine.

See also Crashes for advice on handling engine crashes (specifically around obtaining stack traces, and reporting crashes in AOT Dart code).

Tracing OpenGL calls in Skia

All OpenGL calls in Skia are guarded by either the GR_GL_CALL_NOERRCHECK or GR_GL_CALL_RET_NOERRCHECK macros. Trace events may be added in these macros to trace all GL calls made by Skia, for example in a patch like this.

Due to the number of events traced to the timeline, the trace buffer may be filled up very quickly. Unless you want to see only the traces for the past few frames, use an endless trace buffer (flutter --trace-startup turns on an endless trace buffer).

Also, make sure to run your application with the --trace-skia flag.

Debugging iOS builds with Xcode

If you open your iOS .xcodeproject or .xcworkspace in Xcode, you can set breakpoints e.g. in main.m. From there, you can use lldb to set a breakpoint on the relevant engine source, e.g. (lldb) br set -f FlutterViewController.mm -l 123.

Debugging Android builds with gdb

See https://github.com/flutter/engine/blob/master/sky/tools/flutter_gdb#L13

Logging in the engine

Flutter tool will by default parse out any non-error output from the engine. Error logs will be displayed. Logging is handled though the FML library's logging.h

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