Archie, I had seen the explanation to which you refer, and the grep instruction kinda threw me a curve, so I just opened up my .xsession-errors file in Kate and did some reading, then decided to comment out (precede with #) the lines under the [Blacklist][Lanczos] section relevant to my video card. Voila, desktop effects are restored.
EDIT: Per kjpetrie's sage counsel, I have replaced my user name with asterisks in this post. I really should have known better. Thanks for the catch!
Prior to the loss, my system had been using OpenGL for compositing, and I know from prior experience that Xrender doesn't support the features I want. Fortunately, in my notes, I had recorded where to start looking (namely /home/*****/.kde4/share/config/kwinrc), so that saved me a bunch of time getting started on this one.
I don't think this really solves the problem or addresses my knowledge deficit to this point, though, so I'll read some more before I go ahead and mark this [SOLVED] in case there is more of significance to learn and I, maybe, decide to take a different route toward a better solution.
What threw me was this: grep KWin::CompositingPrefs::detectDriverAndVersion ~/.xsession-errors
That bit with ~/ is a sort of shorthand, but should it not have read ~home/ instead of ~/ ? When I executed the command as written above, it returned no result, and signaled no error, which is why, when I realized where .xsession-errors resides I executed the following:
grep KWin::CompositingPrefs::detectDriverAndVersion /home/*****/.xsession-errors
which still returned nothing. An examination of the file, however, produced what I posted earlier. I had a really rough midnight shift this past week, and it may be affecting how clearly I am thinking right now, so, if I did something stupid, I'm sorry.
I, perhaps, need to become more familiar with how to use grep and with what the Lanczos blacklist is actually there to achieve (some of what Mr. Graesslin said wasn't really all that understandable to me).
Anyhoo, I have a work-around for now, but am blissfully unaware of its unintended consequences. That doesn't give me a warm, fuzzy feeling so I will be digging a little deeper, yeah.