matplotlib-devel

[matplotlib-devel] Polygon vs. Patch

[Benjamin R. <ben...@ou...>]

This might be a stupid question, but what is the difference between a
Polygon and  Patch? A Polygon is subclassed from a Patch. The only real
substantial difference I see is that a Polygon object has logic flagging
and ensuring that it has a closed ring, but does that really merit a whole
new class?

What makes things even more confusing is that RegularPolygon and
CirclePolygon are not even subclassed from Polygon.

I wonder if we might want to consider folding in some of Polygon's
functionality into Patch, and simply let Polygon be an alias for Patch
(after all, a polygon is usually what people think of when they really want
a patch).

Just a thought.

Cheers!
Ben Root

Re: [matplotlib-devel] Polygon vs. Patch

[Stefan H. <shm...@gm...>]

No, a Patch is not automatically a Polygon. You could make a Patch out of
splines or Bezier curves, for example.

Cheers,
Stefan



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Re: [matplotlib-devel] Polygon vs. Patch

[Benjamin R. <ben...@ou...>]

Since Polygon subclasses Patch, wouldn't that mean that a Polygon could be
made out of splines or Bezier curves? I fail to see the "inherent barrier"
for Polygons and Patches to be the same thing. I am not claiming that they
are identical now, I just don't see why a Polygon's functionality needs to
be in a subclass of Patch rather than in Patch itself.


On Mon, Aug 4, 2014 at 2:34 AM, Stefan H. <shm...@gm...> wrote:

> No, a Patch is not automatically a Polygon. You could make a Patch out of
> splines or Bezier curves, for example.
>
> Cheers,
> Stefan
>
>
>
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> View this message in context:
> http://matplotlib.1069221.n5.nabble.com/Polygon-vs-Patch-tp43743p43746.html
> Sent from the matplotlib - devel mailing list archive at Nabble.com.
>
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Re: [matplotlib-devel] Polygon vs. Patch

[Stefan H. <shm...@gm...>]

I do see a clear-cut difference. A Patch is a two-dimensional region
characterized by a boundary and an interior region, which may have colors,
line/hatch styles, etc. Also, a Patch has an algorithms to compute an area,
a circumference, decide whether a point lies inside or outside the Patch, to
cut a Patch for visibility calculations, etc.

A Polygon is a special case of a Patch, namely one that is bounded by
piecewise-linear segments. This implies specific formulae/algorithms to
compute the properties mentioned above.

Now, it is entirely meaningful to realize a Patch differently than in terms
of piecewise-linear segments. I could use piecewise cubic segments
(splines), or give the control points of a closed Bezier curve. All the
properties of a Patch are still meaningful, but none of the algorithms for a
Polygon apply.

Hence I find it meaningful to define

class Polygon(Patch)

such that I am not precluded to define

class SplinePatch(Patch)
class BezierPatch(Patch)
etc.

Hence I prefer to have Patch as an Abstract Base Class and not as a specific
implementation of a Polygon.








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