matplotlib-devel Mailing List for matplotlib

Hi all,
I found a small bug in LineCollection, which gives an exception when setting
alpha. This is manifested in e.g. hlines and vlines:
In [1]: hlines((0,),(-1,),(1,),color='b',alpha=0.1)
---------------------------------------------------------------------------
IndexError Traceback (most recent call last)
XXX/<ipython console> in <module>()
XXX/lib/python/matplotlib/pyplot.py in hlines(*args, **kwargs)
 1700 hold(h)
 1701 try:
-> 1702 ret = gca().hlines(*args, **kwargs)
 1703 draw_if_interactive()
 1704 except:
XXX/lib/python/matplotlib/axes.py in hlines(self, y, xmin, xmax, colors,
linestyles, label, **kwargs)
 2609 linestyles=linestyles,
label=label)
 2610 self.add_collection(coll)
-> 2611 coll.update(kwargs)
 2612
 2613 minx = min(xmin.min(), xmax.min())
XXX/lib/python/matplotlib/artist.py in update(self, props)
 438 if func is None or not callable(func):
 439 raise AttributeError('Unknown property %s'%k)
--> 440 func(v)
 441 changed = True
 442 self.eventson = store
XXX/lib/python/matplotlib/collections.py in set_alpha(self, alpha)
 306 else:
 307 artist.Artist.set_alpha(self, alpha)
--> 308 self._facecolors[:, 3] = alpha
 309 self._edgecolors[:, 3] = alpha
 310
IndexError: invalid index
This appears to be because LineCollection.__init__() only uses
Collection._edgecolors, and sets _facecolors to an empty array. I don't
know if it's the proper solution, but I did this to get it to work:
Index: lib/matplotlib/collections.py
===================================================================
--- lib/matplotlib/collections.py (revision 5000)
+++ lib/matplotlib/collections.py (working copy)
@@ -305,7 +305,8 @@
 except TypeError: raise TypeError('alpha must be a float')
 else:
 artist.Artist.set_alpha(self, alpha)
- self._facecolors[:, 3] = alpha
+ if len(self._facecolors):
+ self._facecolors[:, 3] = alpha
 self._edgecolors[:, 3] = alpha
 def get_linewidths(self):
Best,
Mike

I discovered another blitting bug in backend_qt4agg.py. Qt expects a pixmap 
stringBuffer formatted in ARGB, but mpl formats in RGBA. The qt4 backend 
usually uses the _renderer.tostring_bgra method to return a properly 
formatted buffer:
if QtCore.QSysInfo.ByteOrder == QtCore.QSysInfo.LittleEndian:
 stringBuffer = self.renderer._renderer.tostring_bgra()
else:
 stringBuffer = self.renderer._renderer.tostring_argb()
The problem I am seeing is when we are blitting, and the tostring_bgra is not 
available. The blitting code in backend_qt4agg.py, starting around line 112, 
gets a buffer from a region copied from a bbox:
reg = self.copy_from_bbox(bbox)
stringBuffer = reg.to_string()
qImage = QtGui.QImage(stringBuffer, w, h, QtGui.QImage.Format_ARGB32)
reg does not have a method to swap the byte order, and Qt does not have a 
Format_RGBA32. Could anyone suggest how to swap the byte order?
Thanks,
Darren

Hi,
the doc-string of the axes scatter method is buggy. Somehow the 
svn-conflict messages got committed to the repository:
I mean this
<<<<<<< .working
[...]
=======
[...]
 >>>>>>> .merge-right.r4987
... stuff)
Manuel