[Matplotlib-users] Bug with blitting in Qt4Agg backend

[G J. <gle...@gm...>]

Hello,
I am experiencing a bug when trying to blit a canvas that contains two
axes, one with a line plot and the other with an imshow plot. The
attached example, QtBlitBugDemo.py demonstrates the problem. As is, on
my machine, the
imshow plot updates correctly, but the line plot acts like the
background is not being restored correctly, the lines keep piling up
on top of each other, even though I am explicitly restoring a clean
background before drawing the artist. If I simply comment out the
line:
       self.specPlotB.draw_artist(self.specArtistB)
which draws the imshow artist, the line plot behaves correctly.
I haven't been able to figure out what is causing this behavior.
I am using r5186 from the SVN. The output from running with debug mode
on is below.

Thanks for any help on this.
Glenn

matplotlib data path /usr/lib/python2.5/site-packages/matplotlib/mpl-data
loaded rc file /home/glenn/.matplotlib/matplotlibrc
matplotlib version 0.98pre
verbose.level debug
interactive is False
units is True
platform is linux2
loaded modules: ['numpy.lib.pkgutil', 'numpy.lib.tempfile',
'numpy.ma.types', 'xml.sax.urlparse', 'distutils', 'matplotlib.errno',
'matplotlib.matplotlib', '_bisect', 'numpy.core.defchararray',
'pprint', 'numpy.lib.bz2', 'matplotlib.tempfile',
'distutils.sysconfig', 'ctypes._endian', 'encodings.encodings',
'matplotlib.colors', 'numpy.core.numerictypes', 'numpy.testing.sys',
'numpy.core.info', 'xml', 'numpy.fft.types', 'numpy.ma.operator',
'numpy.ma.cPickle', 'struct', 'numpy.random.info', 'tempfile', 'mmap',
'xml.sax.urllib', 'numpy.linalg', 'numpy.testing.operator', 'imp',
'compiler.sys', 'collections', 'compiler.pyassem', 'numpy.core.umath',
'_struct', 'unittest', 'compiler.new', 'numpy.lib.numpy',
'numpy.testing.types', 'compiler.ast', 'numpy.ma.sys', 'zipimport',
'string', 'numpy.testing.os', 'matplotlib.locale',
'numpy.lib.arraysetops', 'numpy.testing.unittest',
'numpy.lib.inspect', 'encodings.utf_8', 'matplotlib.__future__',
'numpy.linalg.numpy', 'pytz.tzinfo', 'numpy.ctypeslib',
'numpy.testing.re', 'itertools', 'numpy.version', 'numpy.lib.re',
'distutils.re', 'ctypes.os', 'compiler.token', 'numpy.core.os',
'compiler', 'numpy.lib.type_check', 'httplib', 'bisect', 'signal',
'compiler.consts', 'numpy.lib._datasource', 'random',
'numpy.ma.extras', 'token', 'numpy.fft.fftpack_lite', 'shlex',
'ctypes.ctypes', 'xml.sax.xmlreader', 'matplotlib.pytz',
'numpy.__builtin__', 'numpy.testing.shlex', 'dis', 'pytz.tzfile',
'cStringIO', 'zlib', 'numpy.numpy', 'matplotlib.StringIO', 'locale',
'numpy.add_newdocs', 'numpy.lib.getlimits', 'PyQt4',
'compiler.transformer', 'xml.sax.saxutils', 'compiler.struct',
'pkgutil', 'compiler.parser', 'numpy.lib.sys', 'encodings',
'compiler.symbol', 'numpy.lib.io', 'numpy.ma.itertools', 'StringIO',
'dateutil', 'pydoc', 'pytz.cStringIO', 'numpy.imp', 'numpy.ctypes',
'matplotlib.warnings', 'rfc822', 'matplotlib.string', 'pytz.pytz',
'urllib', 'matplotlib.sys', 're', 'numpy.lib._compiled_base',
'numpy.core.mmap', 'new', 'numpy.lib.struct', 'symbol', 'math',
'numpy.fft.helper', 'fcntl', 'numpy.ma.warnings', 'compiler.imp',
'UserDict', 'inspect', 'distutils.os', 'matplotlib', 'urllib2',
'pytz.os', 'fnmatch', 'numpy.lib.info', 'numpy.testing',
'numpy.testing.glob', 'numpy.lib.warnings', 'ctypes.struct', 'codecs',
'numpy.core._sort', 'PyQt4.QtGui', 'compiler.visitor', 'md5',
'_locale', 'matplotlib.sre_constants', 'matplotlib.os', 'thread',
'numpy.lib.ufunclike', 'numpy.core.memmap', 'traceback',
'numpy.core._dotblas', 'numpy.testing.warnings', 'weakref',
'numpy.core._internal', 'numpy.fft.fftpack', 'opcode',
'numpy.core.scalarmath', 'numpy.linalg.lapack_lite', 'ctypes',
'distutils.sys', 'os', 'marshal', 'numpy.lib.shutil', '__future__',
'numpy.core.string', 'matplotlib.copy', 'xml.sax.types',
'numpy.random.numpy', '_sre', 'numpy.lib.gzip', 'numpy.core.sys',
'numpy.random', 'numpy.testing.utils', '__builtin__',
'numpy.lib.twodim_base', 'numpy.ma.core', 'matplotlib.re',
'numpy.core.cPickle', 'base64', 'compiler.dis', 'operator',
'numpy.testing.parametric', 'numpy.core.arrayprint',
'distutils.string', 'ctypes._ctypes', '_heapq', 'ctypes.sys', 'heapq',
'numpy.os', 'posixpath', 'numpy.lib.financial',
'numpy.core.multiarray', 'errno', 'numpy.testing.numpy', '_socket',
'binascii', 'numpy.lib.compiler', 'sre_constants',
'compiler.cStringIO', 'datetime', 'compiler.os', 'matplotlib.md5',
'types', 'pytz.sys', 'tokenize', 'FigureWindow', 'xml.sax.handler',
'numpy.core.numpy', 'numpy', 'numpy.lib.urlparse',
'matplotlib.dateutil', 'numpy.core.defmatrix', 'xml.sax.os',
'cPickle', 'matplotlib.xml', '_codecs', 'numpy.testing.difflib',
'matplotlib.traceback', 'numpy.__config__', 'numpy.fft.info',
'numpy.lib.types', 'pytz', 'matplotlib.pyparsing',
'compiler.copy_reg', 'numpy.ma.numpy', 'copy', 'numpy.core.re',
'socket', '_types', 'numpy.core.fromnumeric', 'hashlib',
'compiler.future', 'matplotlib.cbook', 'numpy.core.copy_reg',
'numpy.lib.scimath', 'numpy.fft', 'numpy.lib', '_ctypes',
'apport_python_hook', 'posix', 'encodings.aliases',
'matplotlib.fontconfig_pattern', 'exceptions', 'sre_parse',
'pytz.bisect', 'sets', 'numpy.core.cStringIO', 'numpy.core.ctypes',
'mimetools', 'distutils.distutils', 'copy_reg', 'sre_compile',
'xml.sax', 'compiler.compiler', '_hashlib', '_random', 'parser',
'site', 'numpy.lib.polynomial', 'numpy._import_tools', 'numpy.glob',
'pytz.struct', 'numpy.lib.time', '__main__', 'compiler.misc',
'numpy.core.records', 'shutil', 'numpy.lib.cPickle', 'numpy.sys',
'matplotlib.weakref', 'numpy.lib.pydoc', 'sip',
'numpy.testing.traceback', 'strop', 'compiler.pycodegen',
'numpy.core.numeric', 'numpy.linalg.info', 'encodings.codecs',
'gettext', 'pytz.datetime', 'numpy.core.__svn_version__',
'numpy.lib.cStringIO', 'numpy.core', 'numpy.testing.info',
'matplotlib.rcsetup', 'matplotlib.time', 'pytz.sets',
'matplotlib.numpy', 'xml.sax._exceptions', 'xml.sax.codecs', 'stat',
'_ssl', 'numpy.lib.utils', 'numpy.lib.index_tricks', 'PyQt4.QtCore',
'warnings', 'encodings.types', 'numpy.lib.math', 'glob',
'numpy.lib.shape_base', 'numpy.core.types', 'numpy.fft.numpy', 'repr',
'sys', 'numpy.core.warnings', 'numpy.lib.urllib2', 'compiler.types',
'numpy.core.__builtin__', 'xml.sax.sys', 'numpy.lib.format',
'numpy.lib.os', 'numpy.ma', 'os.path', 'bz2', 'pytz.gettext',
'numpy.random.mtrand', 'numpy.lib.pprint', 'compiler.symbols',
'matplotlib.datetime', 'matplotlib.distutils', '_weakref',
'numpy.testing.numpytest', 'difflib', 'distutils.errors', 'urlparse',
'linecache', 'matplotlib.shutil', 'numpy.lib.function_base',
'numpy.testing.imp', 'time', 'gzip', 'numpy.lib.machar',
'compiler.marshal', 'numpy.linalg.linalg', 'compiler.syntax']
$HOME=/home/glenn
CONFIGDIR=/home/glenn/.matplotlib
Using fontManager instance from /home/glenn/.matplotlib/fontManager.cache
numerix numpy 1.1.0.dev5077
0.98pre Qt4Agg