bug#55208: 29.0.50; MS-Windows GUI selection dialogs and double-buffering

[Eli Zaretskii]

The double-buffering feature on MS-Windows has one unpleasant
side-effect: when the user opens any GUI selection dialog that is
provided by the MS-Windows "toolkit", dragging that dialog leaves its
"ghost" shown in the Emacs frame.

To reproduce:

 emacs -Q
 Click File->Open File
 Drag the file selection dialog with the mouse
 Observe that the dialog is indeed dragged, as expected, but it leaves
 its "ghost" at the original position

I think this is related to the fact that, as long as the selection
dialog is open, we don't update the Emacs display.  With
double-buffering disabled, the area across which the dialog is dragged
is cleared (the text is not "erased", and only the background
remains).  Which is also not very nice, but it's much more subtle, so
much so that I don't recall any bug reports about this.  Showing the
"ghost" of the menu there is much more prominent, so I hope we could
at least go back to what we have without double-buffering.  Bonus
points for redrawing the text while the dialog is being dragged.



In GNU Emacs 29.0.50 (build 968, i686-pc-mingw32)
 of 2022-05-01 built on HOME-C4E4A596F7
Repository revision: 9370a4763aacbb9278b5be9c92a2484e3652bc29
Repository branch: master
Windowing system distributor 'Microsoft Corp.', version 5.1.2600
System Description: Microsoft Windows XP Service Pack 3 (v5.1.0.2600)

Configured using:
 'configure -C --prefix=/d/usr --with-wide-int
 --enable-checking=yes,glyphs 'CFLAGS=-O0 -gdwarf-4 -g3''

Configured features:
ACL GIF GMP GNUTLS HARFBUZZ JPEG JSON LCMS2 LIBXML2 MODULES NOTIFY
W32NOTIFY PDUMPER PNG RSVG SOUND SQLITE3 THREADS TIFF
TOOLKIT_SCROLL_BARS WEBP XPM ZLIB

Important settings:
  value of $LANG: ENU
  locale-coding-system: cp1255

Major mode: Lisp Interaction

Minor modes in effect:
  tooltip-mode: t
  global-eldoc-mode: t
  eldoc-mode: t
  show-paren-mode: t
  electric-indent-mode: t
  mouse-wheel-mode: t
  tool-bar-mode: t
  menu-bar-mode: t
  file-name-shadow-mode: t
  global-font-lock-mode: t
  font-lock-mode: t
  blink-cursor-mode: t
  line-number-mode: t
  indent-tabs-mode: t
  transient-mark-mode: t
  auto-composition-mode: t
  auto-encryption-mode: t
  auto-compression-mode: t

Load-path shadows:
None found.

Features:
(shadow sort mail-extr emacsbug message mailcap yank-media rmc puny
rfc822 mml mml-sec password-cache epa derived epg rfc6068 epg-config
gnus-util text-property-search time-date seq gv subr-x byte-opt bytecomp
byte-compile cconv mm-decode mm-bodies mm-encode mail-parse rfc2231
mailabbrev gmm-utils mailheader cl-loaddefs cl-lib sendmail rfc2047
rfc2045 ietf-drums mm-util mail-prsvr mail-utils dired dired-loaddefs
face-remap iso-transl tooltip eldoc paren electric uniquify ediff-hook
vc-hooks lisp-float-type elisp-mode mwheel dos-w32 ls-lisp disp-table
term/w32-win w32-win w32-vars term/common-win tool-bar dnd fontset image
regexp-opt fringe tabulated-list replace newcomment text-mode lisp-mode
prog-mode register page tab-bar menu-bar rfn-eshadow isearch easymenu
timer select scroll-bar mouse jit-lock font-lock syntax font-core
term/tty-colors frame minibuffer nadvice simple cl-generic cham georgian
utf-8-lang misc-lang vietnamese tibetan thai tai-viet lao korean
japanese eucjp-ms cp51932 hebrew greek romanian slovak czech european
ethiopic indian cyrillic chinese composite emoji-zwj charscript charprop
case-table epa-hook jka-cmpr-hook help abbrev obarray oclosure
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text-properties overlay sha1 md5 base64 format env code-pages mule
custom widget keymap hashtable-print-readable backquote threads
w32notify w32 lcms2 multi-tty make-network-process emacs)

Memory information:
((conses 16 49989 12437)
 (symbols 48 6902 1)
 (strings 16 19268 3097)
 (string-bytes 1 540461)
 (vectors 16 11301)
 (vector-slots 8 161753 13124)
 (floats 8 25 198)
 (intervals 40 340 71)
 (buffers 888 10))