Center isn't centered

[ljwolf]

The way I implemented "center", it doesn't actually center-align the legend, it only pins the legend to a center coordinate.

So, if you wanted a "center-aligned" legend, you'd need to specify the legend location to the left & set the width to span the figure.

Instead, I should probably implement centering as true centering with respect to image, as well as ensure that right-align is on the right edge of the image.