Unable to get transparent region using patch(...)

[Troy Vine]

Hi,

I am using octave 3.2.2 on OS X 10.5.8 installed using the standard  
installer.  Using the code below, I attempted to create a shaded  
region transparent to the plotted line.  With both X11 and AquaTerm  
(version 1.0.1) the shaded region is opaque to the plot underneath.   
If I execute the command

> get(p, 'facealpha')

afterwards then I get 0.2 as expected.  What am I doing wrong?

Many thanks,

Troy



> x = [0:pi/12:2*pi];
> plot(x, sin(x))
> xp = [2 2 3 3];
> yp = [ylim fliplr(ylim)];
> p = patch(xp,yp, 'r');
> set(p,'facealpha',0.2);