Michael Droettboom wrote:
> This is a very good test to have -- we should add it to backend_driver.py.
>
> FWIW, SVG appears to behave similarly to PDF, and has a "miter-limit"
> property to control when to bevel vs. miter when the mode is set to
> "miter". (Though the default threshold appears to be different.) I
> didn't look into Ps, but it may have a similar configuration.
>
> Agg also has a miter limit (which is not currently settable from
> Python), but it reverts to what it calls "smart" beveling, rather than
> regular beveling when below that limit. It does, however, have another
> miter mode called "miter_join_revert" which doesn't do smart beveling.
> (Try the "conv_stroke" example in the Agg source). In fact, it has this
> comment associated with it (agg_math_stroke.h:275):
>
> // For the compatibility with SVG, PDF, etc,
> // we use a simple bevel join instead of
> // "smart" bevel
>
> I think there is an argument to be made that we should use this mode
> instead in the Agg backend, to be consistent with PDF and SVG (see patch
> below).
>
> On a higher level, however, I am a bit concerned about this miter limit
> concept. It seems a bit dangerous for scientific plots: there is a
> large change in the look of the corner after only a small change in
> angle around the miter limit threshold. It may make the data appear to
> have large changes where in fact the changes are small. This seems like
> an argument of "bevel" or "round" as the default line join (it is
> currently "miter"). I also like the idea of "round" join keeping the
> corner close to the actual data point.
>
> Now, if the user wants miter joins, they can, but I would suggest that
> we set the miter-limit threshold in all backends high enough such that
> it "always miters" and "never bevels". I can't see why (for other than
> artistic purposes), one would want to sometimes miter or bevel depending
> on angle in a scientific plot. We can expose miter limit as a parameter
> somehow, but for a default, I think it should be "always miter". What
> do you think?
Mike,
Everything you said above sounds right to me, for plotting data--round
joins are likely to provide a good combination of aesthetics and
faithfulness to the data. Miters are needed for things like arrows
(e.g. in quiver), and pcolor patches.
Eric
>
> Cheers,
> Mike
>
> Index: _backend_agg.cpp
> ===================================================================
> --- _backend_agg.cpp (revision 6731)
> +++ _backend_agg.cpp (working copy)
> @@ -209,7 +209,7 @@
> std::string joinstyle = Py::String( gc.getAttr("_joinstyle") );
>
> if (joinstyle=="miter")
> - join = agg::miter_join;
> + join = agg::miter_join_revert;
> else if (joinstyle=="round")
> join = agg::round_join;
> else if(joinstyle=="bevel")
>
> Jouni K. Seppänen wrote:
>> Michael Droettboom <md...@stsci.edu>
>> writes:
>>
>>
>>> Passing solid_joinstyle='bevel' does resolve the problem on both 0.91.x
>>> and 0.98.x. Additionally, path simplification (which is a new feature
>>> on 0.98.x) also resolves this problem (set rcParam path.simplify to True).
>>>
>> It seems that agg and pdf have different ways to render small angles
>> when the join style is 'miter'. Pdf has a limit (settable in the pdf
>> file) beyond which it reverts to bevel-style angles, agg seems to always
>> do the miter join but cuts it off at some distance.
>>
>> Here's a test script, and screenshots of (a part of) the agg and pdf
>> outputs when the join style is 'miter'.
>>
>>
>> ------------------------------------------------------------------------
>>
>> ------------------------------------------------------------------------
>>
>> ------------------------------------------------------------------------
>>
>> ------------------------------------------------------------------------------
>> ------------------------------------------------------------------------
>>
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