picking bug in SVN with old masked array

I just ran into a bug with picking of lines. I changed the line style in
figure 1, subplot 1 to 'o-' (from 'o') and ripped out most of everything
else in examples/pick_event_demo.py to create pick_event_demo3.py
(attached). When I run this and I attempt to click on points, I get

Traceback (most recent call last):
  File
"/home/astraw/py2.5-linux-x86_64/lib/python2.5/site-packages/matplotlib/backends/backend_gtk.py",
line 193, in button_press_event
    FigureCanvasBase.button_press_event(self, x, y, event.button)
  File
"/home/astraw/py2.5-linux-x86_64/lib/python2.5/site-packages/matplotlib/backend_bases.py",
line 915, in button_press_event
    self.callbacks.process(s, mouseevent)
  File
"/home/astraw/py2.5-linux-x86_64/lib/python2.5/site-packages/matplotlib/cbook.py",
line 157, in process
    func(*args, **kwargs)
  File
"/home/astraw/py2.5-linux-x86_64/lib/python2.5/site-packages/matplotlib/backend_bases.py",
line 849, in pick
    self.figure.pick(mouseevent)
  File
"/home/astraw/py2.5-linux-x86_64/lib/python2.5/site-packages/matplotlib/artist.py",
line 220, in pick
    for a in self.get_children(): a.pick(mouseevent)
  File
"/home/astraw/py2.5-linux-x86_64/lib/python2.5/site-packages/matplotlib/axes.py",
line 2155, in pick
    martist.Artist.pick(self,args[0])
  File
"/home/astraw/py2.5-linux-x86_64/lib/python2.5/site-packages/matplotlib/artist.py",
line 220, in pick
    for a in self.get_children(): a.pick(mouseevent)
  File
"/home/astraw/py2.5-linux-x86_64/lib/python2.5/site-packages/matplotlib/artist.py",
line 214, in pick
    inside,prop = self.contains(mouseevent)
  File
"/home/astraw/py2.5-linux-x86_64/lib/python2.5/site-packages/matplotlib/lines.py",
line 327, in contains
    ind = segment_hits(mouseevent.x,mouseevent.y,xt,yt,pixels)
  File
"/home/astraw/py2.5-linux-x86_64/lib/python2.5/site-packages/matplotlib/lines.py",
line 100, in segment_hits
    candidates = candidates & ~point_hits[:-1] & ~point_hits[1:]
TypeError: bad operand type for unary ~: 'MaskedArray'

Anyhow, I spent a little while tracking this down and came up with the
attached patch. I guess there's a more direct solution to the issue that
this band-aid, but I hope this will jump-start someone to fix this. In
the meantime, this appears to work sufficiently for my purposes...

FWIW, my numpy is SVN from 16 december 2007 (after 1.0.4 and thus on the
way to 1.0.5) and I'm using the old ma module.

BUILDING MATPLOTLIB
            matplotlib: 0.98pre
                python: 2.5.1 (r251:54863, Oct 5 2007, 13:50:07) [GCC
                        4.1.3 20070929 (prerelease) (Ubuntu
                        4.1.2-16ubuntu2)]
              platform: linux2

REQUIRED DEPENDENCIES
                 numpy: 1.0.5.dev
             freetype2: 9.16.3

pick_event_demo3.py (637 Bytes)

fixup_masked_for_picking.patch (910 Bytes)

Thanks for finding this. I just committed a slightly less band-aid-like fix in SVN r4979.

There were really two bugs here:

1) A masked array is created for a line plot whenever only y values are provided, even if there are no masked values in the data. That would only be a performance bug if it weren't for...

2) The picking code for a line assumes non-masked arrays. Since the Line class already keeps around a "compressed" version of the data for drawing, it is easy enough to use that instead of the raw data.

By fixing 1), 2) is no longer even an issue in your example. However, for a plot that really does have gaps, 2) needs to be fixed as well.

Cheers,
Mike

Andrew Straw wrote:

···

I just ran into a bug with picking of lines. I changed the line style in
figure 1, subplot 1 to 'o-' (from 'o') and ripped out most of everything
else in examples/pick_event_demo.py to create pick_event_demo3.py
(attached). When I run this and I attempt to click on points, I get

Traceback (most recent call last):
  File
"/home/astraw/py2.5-linux-x86_64/lib/python2.5/site-packages/matplotlib/backends/backend_gtk.py",
line 193, in button_press_event
    FigureCanvasBase.button_press_event(self, x, y, event.button)
  File
"/home/astraw/py2.5-linux-x86_64/lib/python2.5/site-packages/matplotlib/backend_bases.py",
line 915, in button_press_event
    self.callbacks.process(s, mouseevent)
  File
"/home/astraw/py2.5-linux-x86_64/lib/python2.5/site-packages/matplotlib/cbook.py",
line 157, in process
    func(*args, **kwargs)
  File
"/home/astraw/py2.5-linux-x86_64/lib/python2.5/site-packages/matplotlib/backend_bases.py",
line 849, in pick
    self.figure.pick(mouseevent)
  File
"/home/astraw/py2.5-linux-x86_64/lib/python2.5/site-packages/matplotlib/artist.py",
line 220, in pick
    for a in self.get_children(): a.pick(mouseevent)
  File
"/home/astraw/py2.5-linux-x86_64/lib/python2.5/site-packages/matplotlib/axes.py",
line 2155, in pick
    martist.Artist.pick(self,args[0])
  File
"/home/astraw/py2.5-linux-x86_64/lib/python2.5/site-packages/matplotlib/artist.py",
line 220, in pick
    for a in self.get_children(): a.pick(mouseevent)
  File
"/home/astraw/py2.5-linux-x86_64/lib/python2.5/site-packages/matplotlib/artist.py",
line 214, in pick
    inside,prop = self.contains(mouseevent)
  File
"/home/astraw/py2.5-linux-x86_64/lib/python2.5/site-packages/matplotlib/lines.py",
line 327, in contains
    ind = segment_hits(mouseevent.x,mouseevent.y,xt,yt,pixels)
  File
"/home/astraw/py2.5-linux-x86_64/lib/python2.5/site-packages/matplotlib/lines.py",
line 100, in segment_hits
    candidates = candidates & ~point_hits[:-1] & ~point_hits[1:]
TypeError: bad operand type for unary ~: 'MaskedArray'

Anyhow, I spent a little while tracking this down and came up with the
attached patch. I guess there's a more direct solution to the issue that
this band-aid, but I hope this will jump-start someone to fix this. In
the meantime, this appears to work sufficiently for my purposes...

FWIW, my numpy is SVN from 16 december 2007 (after 1.0.4 and thus on the
way to 1.0.5) and I'm using the old ma module.

BUILDING MATPLOTLIB
            matplotlib: 0.98pre
                python: 2.5.1 (r251:54863, Oct 5 2007, 13:50:07) [GCC
                        4.1.3 20070929 (prerelease) (Ubuntu
                        4.1.2-16ubuntu2)]
              platform: linux2

REQUIRED DEPENDENCIES
                 numpy: 1.0.5.dev
             freetype2: 9.16.3

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