Windows does not support semi transparency for enhanced metafiles (*.emf)

n <- 4
g <- make_ring(n)

     layout = layout_in_circle(g),
     vertex.label    = letters[1:n],    
     edge.width      = 4,
     edge.label      = seq(n),
     edge.color      = c(rep("#66666660", n-1), "#FF0000") 
# Save to .emf  in Windows does not preserve semi-transparency.
# Only the red edge is visible in the saved file.
## Select output window and save file as (*.emf)
## >warnings()
## Warning message:
## semi-transparency is not supported on this device: reported only once per page

Just curious: is semi transparency for (*.emf) files supported on other platforms ?

As far as I know the file format itself supports full transparency and opacity only (source). So I’d be highly surprised if it turns out that it works on other platforms but not on Windows (especially because emf isn’t really used outside the Windows world).

EMF-plus supports semi-transparency (opacity). This could be implemented on other platforms. Both file formats have the extension .emf.

I am using RGui (64) under Windows.
When I create a plot and select the active output device, under right-click (RMB) I see the following choices: copy as metafile, copy as bitmap, save as metafile and save as bitmap.

However, under File > Save as > more formats appear to be available, including PDF, Png and Jpeg. So using metafile is not necessary.