On 7/6/07, Eric Firing <[EMAIL PROTECTED]> wrote:
> 2) polar_demo.py: the part of the spiral outside the bounding circle is
> removed in the Agg version but not in the Cairo version.
This is a fairly new feature I added to add -- clipping to a polygon.
I haven't ported it to postscript yet. The GraphicsContext now has a
clip_path attribute, which is an agg path storage instance. Even
though it is an agg object (not related to backend_agg actually,
separate code base and wrapping) Eg if we construct a path with
from matplotlib import agg
path = agg.path_storage()
path.move_to(10,10)
path.line_to(100,100)
path.line_to(200,200)
path.line_to(100,200)
path.close_polygon()
We can access it from python code like
In [62]: for i in range(path.total_vertices()):
....: cmd, x, y = path.vertex(i)
....: print cmd, x, y
....:
1 10.0 10.0
2 100.0 100.0
2 200.0 200.0
2 100.0 200.0
79 0.0 0.0
Where each of the cmd is an integer given by one of the path commands
In [60]: for name in dir(agg):
....: if not name.startswith('path_cmd'): continue
....: print name, getattr(agg, name)
....:
path_cmd_catrom 6
path_cmd_curve3 3
path_cmd_curve4 4
path_cmd_curveN 5
path_cmd_end_poly 15
path_cmd_line_to 2
path_cmd_mask 15
path_cmd_move_to 1
path_cmd_stop 0
path_cmd_ubspline 7
The final command "79" which is the result of the
path.close_polygon() function call is a mask of two flags
In [65]: agg.path_flags_close | agg.path_cmd_end_poly
Out[65]: 79
Steve had expressed some dissatisfaction in using the agg python
object for path storage, because agg is C++ whereas cairo is C, and it
just feels wrong to be using an agg path for cairo, but at the end of
the day, we faced either rolling our own backend independent path
object or reusing one, and since agg is fairly deeply ingrained into
mpl and unlikely to disappear, I decided to do a backend independent
SWIG wrapping of agg that could be used across backends to expose some
of the data structures and functionality (eg image interpolation, path
structures, whatever). The idea was to eventually get rid of backend
agg entirely and replace it with backend_agg2 which uses the SWIG
python layer and thereby exposing more of agg's general functionality
at the python/user layer. Unfortunately, this project has stalled and
we currently have the agg layer but are not using it for agg backend
rendering, which is still done in the custom CXX extension code.
The agg path structure is used very lightly currently at the python
level, so if folks fine this arrangement problematic we can
reconsider.
JDH
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