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DEBUGGING.md

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Debugging

By default, our use of Python's logging module is noisy about errors, warnings, and general informational stuff, but silent about anything with a lower priority. To see all messages, set the MYPAINT_DEBUG environment variable.

MYPAINT_DEBUG=1 ./mypaint -c /tmp/cfgtmp_throwaway_1

MyPaint normally logs Python exception backtraces to the terminal and to a dialog within the application.

To debug segfaults in C/C++ code, use gdb with a debug build, after first making sure you have debugging symbols for Python and GTK3.

sudo apt-get install gdb python2.7-dbg libgtk-3-0-dbg
DEST=$(mktemp -d)
python setup.py build_ext --debug --force install --root=$DEST --prefix=.
echo "Debug build installed in $DEST"
MYPAINT_DEBUG=1 gdb -ex run --args python $DEST/bin/mypaint -c $DEST

Omit the --force flag if you don't need to rebuild mypaintlib.

Install pythonX-dbg depending on the version of python you use.

Check the version by running python --version

Execute bt within the gdb environment for a full backtrace. See also: https://wiki.python.org/moin/DebuggingWithGdb

Profiling

MyPaint can run the cProfile code profiler interactively if you find that performance is lagging in a particular area, and want to figure out what functions need optimizing. Assigning the "Start/Stop Profiling..." command to a spare function key like F9 allows profiling to be flipped on and off quickly while you do something that needs profiling.

When profiling stops, MyPaint creates a temporary output folder and writes its output files there. It then opens the temp folder in your desktop environment's file and directory browser. You get a single uniquely named temporary profiling folder for each instance of MyPaint you run.

One word of warning: the temporary folders are removed at the end of the MyPaint session to avoid tempdir clutter. If you need to keep the profiler's output, be sure to copy them safely somewhere first.

The most convenient output we support is graphical (PNG format). Install gprof2dot.py and graphviz for the prettiest results. If you need to run the commands manually on .pstat output, try:

gprof2dot.py -f pstats -o output.dot output.pstat
dot -Tpng -o output.png output.dot

Our profiler tries to do this for you.