alpha bug in Polygon

If the color of a polygon is set to ‘none’ (meaning no fill), the alpha set for that polygon doesn’t seem to apply to the boundary of that polygon. To see this, change the following line in (in the matplotlib gallery):

poly = Polygon(verts, facecolor=‘0.8’, edgecolor=‘k’)


poly = Polygon(verts, facecolor=‘k’, edgecolor=‘k’,alpha=0.1)

in this case, the alpha is applied to both the fill and the edge. Now change that same line to

poly = Polygon(verts, facecolor=‘none’, edgecolor=‘k’,alpha=0.1)

And then there is no fill as expected, but the edge is now dark black again instead of being light due to the alpha of 0.1.


Daniel Hyams