Re: Redisplay problems?

[Stefan <monnier@iro.umontreal.ca>]

> When the display is messed up (for some value of "messed up"), we
> cannot trust the current glyph matrices anymore.

It all depends on the reason for the "messed up".  E.g. it can be messed
up because some code drew something on screen without going through
"change matrices and reflect that change on screen".  That's what
I would understand as the "natural meaning" for "garbaged" (and in that
case the matrices might still be trusted to reflect "what we'd like to
see on screen").

So, IIUC this "natural meaning" is wrong.  And "garbaged" is really
meant to say "disable all optimizations".
Which then begs the question: what is the difference with
`prevent_redisplay_optimizations_p'?

>> > think you need to call expose_frame, and arrange for the exposed
>> > rectangle to cover the entire frame.  That should do what you want, no
>> > more, no less.
>> Doesn't the windowing-system do that already for us?
> If you mean that it somehow magically calls expose_frame, then no, I
> don't think so.

No, I mean that the windowing-system should already arrange to send us
the relevant expose events (which could be "no events at all", if the
windowing system were to draw the frame from some backed up copy).

> I'm not an expert on those parts of Emacs, but it looks to me that we
> don't consistently call expose_frame when a frame is deiconified.

Indeed and I think that's right because the expose_frame calls will be
performed later in response to expose events.


        Stefan