On 15.08.21 09:37, Robert wrote:
> Firstly, make sure you have the correct zone display option selected
> using the buttons on the left-hand toolbar.

It was only after posting that I found that. It was on the top one, 
"Show filled areas in zones", which sounds right.

> Secondly, for a zone to fill it must have a net associated with it,
and> there must be a pad or track within the zone area that is on the
same
> net.   Right click on the zone edge to edit its properties
(including
> its associated net).   You may need the adjust the clearances, to
ensure
> the zone is not blocked from connecting to pads, though usually the
> defaults are OK in that respect.

I had selected "GND" for the zone. Checking "properties" of the zone 
confirms that. The entire GND network, with through-hole pads, SMD
pads, and a whole bunch of tracks is inside the zone. That's 17 pads
and many tracks. (I'd connected them all, just in case the airwires
had been the holdup.)

The manual talks about segment fill, rather than polygon, being a
safer  bet, so I've just tried that, using the fill option after a
right click on the  zone edge. Still no visible fill. I think the
window which flashes up is a  progress bar. I had enabled use of
graphic acceleration earlier. Kicad  does appear to think it is
rendering the fill. Does it do that concurrently  with the progress
display, or after?

We must be narrowing the set of possible causes. How many can remain?

Many thanks for taking a look at this peculiarity.

 Erik