fix fancy-style annotation causing an exception when the connecting path

[leejjoon]

This issue is originally reported by brenbarn@brenbarn.net on the user mailing list.

http://www.mail-archive.com/matplotlib-users@lists.sourceforge.net/msg22443.html

This happens when the connecting path is too short compared to the arrow head length.
The patch fixes this problem.

[mdboom]

@leejjoon: I received this private e-mail from Rolf Barinka, and I think you may be the most appropriate person to address it.

Hello Michael Droettboom

I found a bug in matplotlib 1.1.1.
And I offer a bugfix.

I am not part of the development team and don't want to be.
So I offer my bugfix to you, because i saw you involved with the bug.

I used matplotlib 1.1.0 and saw this exception:
a long traceback culminating in
/usr/lib64/python2.7/site-packages/matplotlib/bezier.py",
line 129, in find_bezier_t_intersecting_with_closedpath
     raise ValueError("the segment does not seemed to intersect with the path")

I googled and found the "Pull Request #566" for matplotlib, which seemed to solve
the problem:
"fix fancy-style annotation causing an exception when..."
<https://github.com/matplotlib/matplotlib/pull/566>

I installed matplotlib 1.1.1 incl. #566.
The bug stayed alive.

In #566 a new exception NonIntersectingPathException was created.
This exception was caught in patches.py: Fancy.transmute().

But in my case the exception occurred in patches.py: Simple.transmute().
So I catch it there and do something to work around.
I am not sure that my workaround is okay for all cases.
It works for my application.

Please consider my bugfix:

41# diff /home/bai/software/matplotlib-1.1.1/lib/matplotlib/patches.py /usr/lib64/python2.7/site-packages/matplotlib/patches.py
3404,3405c3404,3409
<             arrow_out, arrow_in = \
<                        split_bezier_intersecting_with_closedpath(arrow_path,
---

            from bezier import NonIntersectingPathException

          try:
               arrow_out, arrow_in = \
                          split_bezier_intersecting_with_closedpath(arrow_path,
3407a3412,3418
            except NonIntersectingPathException:
                arrow_out = arrow_path
                dx, dy = x2 - x1, y2 - y1
                ff = head_length/(dx*dx+dy*dy)**.5
                x0, y0 = x2 - ff*dx, y2 - ff*dy
                arrow_path = [(x0, y0), (x1, y1), (x2, y2)]
                arrow_in = arrow_path

And please tell me what you think about it.

[leejjoon]

Michael, can you contact Rolf Barinka and ask if he/she can send an example script that reproduces this error?

[barinka]

@leejjoon: Hello, this is Rolf Barinka.

The code that brings the exception is part of a complex application, and it is hard to seperate.

---

I put some prints into patches.py and bezier.py:

    def transmute(self, path, mutation_size, linewidth):
        ...
    try:
           ...
        except NonIntersectingPathException:
    print 'NonIntersectingPathException'
            ....

def find_bezier_t_intersecting_with_closedpath(bezier_point_at_t, inside_closedpath,
t0=0., t1=1., tolerence=0.01):
...
if not xor(start_inside, end_inside):
print 't0=', t0, ' t1=', t1, ' tol=', tolerence
print 'start=', start, ' end=', end
print 'start_inside=', start_inside, ' end_inside=', end_inside
raise NonIntersectingPathException("the segment does not seemed to intersect with the path")

---

Now some parts of my script, that raise the exception:

def pol2kar(w, r):
"polar [grad,mm] --> karthesisch [x,y]"
if type(w) is list:
phi = [ a / fakt for a in w ]
else:
phi = w / fakt
return (r * np.cos(phi), r * np.sin(phi))

def pfeil(ax, r,v, col, xM=0, yM=0):
"""Pfeil malen
PolKoo color"""
print 'r=', r, ' v=', v
(xp, yp) = pol2kar(r, v)
print 'xM,yM=', xM, yM
x = [ a + xM for a in xp ]; y = [ b + yM for b in yp ]
rad = 0.0680529
cs = 'arc3, rad=%g' % rad
d = dict(arrowstyle='simple', connectionstyle=cs, alpha=0.2, fc=col, ec='none')
print 'x=', x, ' y=', y
print 'd=', d
ax.annotate('', xy=(x[2], y[2]), xytext=(x[0], y[0]), arrowprops=d)

r = [220, 222, 226]
v = [-322.455, -322.455, -320.189]

we need an Axes object "ax" and a color "col"

this brings the exception:

pfeil(ax, r, v, col)

---

This was the output:
r= [220, 222, 226] v= [-322.455, -322.455, -320.189]
xM,yM= 0 0
x= [247.01486090593005, 239.63076469931315, 222.42196897889596] y= [207.270078681473, 215.76450967344562, 230.32469133063231]
d= {'connectionstyle': 'arc3, rad=0.0680529', 'alpha': 0.2, 'fc': '#DD0000', 'arrowstyle': 'simple', 'ec': 'none'}
t0= 0.0 t1= 1.0 tol= 0.01
start= (396.80739712418909, 350.43678238448041) end= (402.37062135854825, 346.84973645969643)
start_inside= True end_inside= True
NonIntersectingPathException

[leejjoon]

Rolf, please test with my proposed change above. Let us know if things work okay in your side.

[barinka]

Hello

Yes, things work okay for me.
Your arrow looks like mine.

Jae-Joon Lee schrieb Folgendes am 2012-08-21 20:58:

Rolf, please test with my proposed change above. Let us know if things work okay in your side.

—
Reply to this email directly or view it on GitHub #566 (comment).

Freundliche Grüße
Rolf Barinka
Abt: AHPS
Fon: 5713