Removing shadows underneath windows when using xcompmgr

[Joel Feiner]

It appears that xcompmgr draws the shadows underneath windows, not just
out to the sides.  I do not like this behavior when it comes to
transparency because you get a window with a lot of gray in it, even if
it's over a white background.  I tried commenting out the section of
code in make_shadow() that fills the whole
shadow image, so that all that's left is the code for filling in the
sides, tops and corners.  It seemed like that would do the trick, but it
turns out that the shadows for the sides, tops and corners extend a
little bit underneath the window.

After a little bit of playing around, it seems like what I want is
difficult to achieve.  I can't seem to figure out how to ignore the
portions of the shadow that are directly under the window.  There are a
variety of offsets and scalings in the make_shadow() function that make
it very difficult to avoid putting shadow data underneath the window itself.

Has anybody tried to fix this bug/misfeature with any success?  Or
perhaps someone has some insight into how all the offset and scalings
work so that I can implement it myself.