Return a Patch object in PointPixelRegion.as_artist()?

[adonath]

Currently the objects returned by PointPixelRegion.as_artist() and e.g. CirclePixelRegion.as_artist() are different. In one case a Line2D object is returned, while in the other it is a Patch object. This will always require an extra check when looping over or plotting multiple regions the Line2D plotting arguments are different than the ones for Patch. E.g. facecolor and edgecolor will work for Patch, but the corresponding argument for Line2D are markeredgecolor and markerfacecolor instead. So one typically ends up with code like:

for region_pix in regions_pix:
    
    if isinstance(region, PointSkyRegion):
        artist = region_pix.as_artist(**kwargs_line2d)
    else:
        artist = region_pix.as_artist(**kwargs)

    ax.add_artist(artist)

I was wondering whether is is possible to unify the behavior, such that the special cases are not needed anymore. I guess what is convenient for the Line2D object is the ability to work with different marker styles (points, stars, triangles etc.), which would be good to keep. From a quick search it seems there is no MarkerPatch in matplotlib, which is unfortunate. @keflavich suggested to use a PathPatch, however this might require a lot of additional code, to achieve what Line2D already does. A compromise might be to maybe allow for an alias of the most common Patch properties, like:

ARTIST_TO_LINE_PROPERTIES = {
    "color": "markeredgecolor",
    "edgecolor": "markeredgecolor",
    "ec": "markeredgecolor",
    "facecolor": "markerfacecolor",
    "fc": "markerfacecolor",
    "linewidth": "markerwidth",
    "lw": "markerwidth",
}

[keflavich]

Ah, my proposal was because I was thinking Line2D was for actual line segments, not point collections. There may be a more appropriate patch type than Line2D for Point regions. I don't love the idea of maintaining our own matplotlib keyword alias lists.

[adonath]

@keflavich I agree maintaining and our matplotlib keyword alias is far from ideal. I guess the object we are looking for is a MarkerPatch, which does not seem to exist. Maybe it is even worth opening a feature request to matplotlib...

[keflavich]

Are there Collection objects that behave like patches?

[adonath]

Are there Collection objects that behave like patches?

Not exactly, but I think the behavior of e.g. a LineCollection and CircleCollection should be uniform.