Hollow markers are not transparent

还没有人认领这个 Issue。

Hello,

When I tried to plot hollow markers on the map, the marker is actually filled, not transparent. See this map below:


Below is the code to reproduce this map:

```python
import matplotlib.pyplot as plt
from mpl_toolkits.basemap import Basemap

lon_ll = -124.5 # lower left corner, longitude
lon_ur = -105.2 # upper right corner, longitude
lat_ll = 32.0 # lower left corner, latitude
lat_ur = 42.0 # upper right corner, latitude

f = plt.figure(dpi=100)
ax = plt.axes()

m = Basemap(llcrnrlon=lon_ll,llcrnrlat=lat_ll,
urcrnrlon=lon_ur,urcrnrlat=lat_ur,\
rsphere=(6378137.00,6356752.3142),\
resolution='c',projection='merc',\
lat_0=(lat_ll+lat_ur)/2,\
lon_0=(lon_ll+lon_ur)/2,lat_ts=20.,
epsg = 3310)

m.arcgisimage(service='World_Physical_Map', xpixels=120, epsg=3310, verbose=False)

m.drawstates()

LA = (34.05, -118.25)
LV = (36.175, -115.136389)
SF = (37.783333, -122.416667)
PH = (33.45, -112.066667)

ms = 15
alpha = 0.75

m.plot(*m(LV[1], LV[0]), marker='s', ms=ms,
ls='none', mew=1.25,c='blue', fillstyle='none', alpha=alpha)
m.plot(*m(LA[1], LA[0]), marker='o', ms=ms,
ls='none', mew=1.25,c='red', fillstyle='right', alpha=alpha)
m.plot(*m(PH[1], PH[0]), marker='o', ms=ms,
ls='none', mew=1.25,c='green', fillstyle='full', alpha=alpha)
m.plot(*m(SF[1], SF[0]), marker='o', ms=ms,
ls='none', mew=1.25,c='cyan', fillstyle='left', alpha=alpha,
markerfacecoloralt='white')

horiz_offset = 0.6 # unit: degrees
plt.text(*m(LA[1] + horiz_offset, LA[0]), 'Los Angeles')
plt.text(*m(LV[1] + horiz_offset, LV[0]), 'Las Vegas')
plt.text(*m(SF[1] + horiz_offset, SF[0]), 'San Francisco')
plt.text(*m(PH[1] + horiz_offset, PH[0]), 'Phoenix')
```

The markers for Los Angeles and Las Vegas should have been hollow (on the left side for LA, and fully for LV), but they are not. For half-full markers, such as the marker for San Francisco, I can set the `markerfacecoloralt` to other colors, but not for fully open markers.

- Operating system: Windows 10
- Python version: 3.6.6
- Basemap version: both 1.1.0 and 1.2.0 have this issue
- matplotlib version: 2.2.2

Note that I used to *not* have this issue some time ago, with older versions of matplotlib (I don't remember which).

首先，使用列出的 Basemap 和 matplotlib 版本运行提供的 Python 复现代码，重点关注 m.plot 入口点以及空心、半填充和全填充标记。将渲染输出与 issue 中描述的预期透明度进行比较，然后验证空心标记会以无填充的方式渲染，同时其他标记样式保持不变。

由索引模型根据 Issue 内容生成。