[Matplotlib-users] Arrow class

[Dominique O. <Dom...@po...>]

Hi,

Based on John's advice in a previous post about designing an Arrow class 
(http://sourceforge.net/mailarchive/message.php?msg_id=9962785), i have 
restarted from scratch, defining the stem as a Line2D instance and the 
head as a RegularPolygon instance (for now, a triangle).

I can correctly set the orientation of the arrow head, and from 
debugging information, the class seems to be basically working. The 
class is imported in axes.py and i have defined the new methods 
add_arrow() and arrow()  in Axes. Arrows are stored in a list called 
arrows (i know John advised to avoid the overhead of that---i am simply 
trying to get it to work first).

Now, i know i am missing something (and this must be at the heart of 
matplotlib): how are 'figure coordinates' transformed into 'axes 
corrdinates'? I guess it has to do with the 'transforms' module but.... 
For instance, if i say

    arrow( [0,1], [0,1] )

with the intent of drawing an arrow from (0,0) to (1,1), i can't see the 
graphical result. Now if i say

    arrow( [0,100], [0,100] )

I can see something (the arrow head). And this may or may not be the 
source of my 2nd problem: the arrow head is drawn, but not the stem (as 
in the thread linked to above). The draw() method of my Arrow class is 
very simple:

    self._stem.draw(renderer)
    self._head.draw(renderer)

Any help would be greatly appreciated. I'll be happy to add spiff to the 
Arrow class once i have a basic version of it working and contribute it 
to matplotlib.

I can post some code if you would like; i just thought it would be too 
long in a mailing list...

Thanks,
Dominique

ps: Thanks for the matplotlib manual!


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