bug#52929: 27.1; Images are sometimes not fully displayed

[Markus Triska]

Dear all,

to reproduce this issue, please download the following image:

    https://www.metalevel.at/ei/202202.png

Then start Emacs with

    $ emacs -Q

and evaluate the form that follows below.

Please note that the image has geometry 202x202. The form creates a
frame with this height and width. It uses a default face with height 1px
to allow pixel exact resizing of the frame. The snippet then waits for a
keypress, and then deletes the frame again.

The frame is large enough to display the image fully, including the thin
border that is drawn around the image. This can be seen by changing
"(setq cursor-type nil ..." to "(setq cursor-type t ..." in the snippet,
in which case the image is fully shown in the frame.

Yet, with the snippet as shown below, the thin border around the image
is not shown at the right margin of the image: You can see that the
frame appears fully white at the right, whereas all other margins of the
image (left, top and bottom) do display the very thin black border fully.

If the following line, which is commented out in the snippet, is
enabled, i.e., if the width is increased by exactly 1 pixel, then also
the thin border on the right is fully shown:

    (set-frame-width frame (1+ width) nil t)

If possible, I would prefer Emacs to show the image fully also if its
exact dimensions (202x202) are used for the frame size. Is there a way
to do this?

Thank you a lot, and Happy New Year 2022!
Markus

    (let* ((width 202)
           (height 202)
           (frame (make-frame `((parent-frame . ,(selected-frame))
                                (minibuffer . nil)
                                (left . 100)
                                (top . 100)
                                (internal-border-width . 0)
                                (vertical-scroll-bars . nil)
                                (left-fringe . 0)
                                (right-fringe . 0)
                                ;; not setting the width/height causes
                                ;; mode line flickering (see #52666)
                                (width . (text-pixels . ,width))
                                (height . (text-pixels . ,height))))))
      ;; set 1 pixel height default face, to allow pixel exact resizing
      ;; of the frame
      (set-face-attribute 'default frame :height 10) 
      ;; set the height and width again, since set-face-attribute
      ;; resizes the frame
      (set-frame-width frame width nil t)
      ;; enable the following line to display the border fully
      ;; (set-frame-width frame (1+ width) nil t)
      (set-frame-height frame height nil t)
      (with-selected-frame frame
        (switch-to-buffer (get-buffer-create "Happy New Year 2022!"))
        (setq cursor-type nil
              mode-line-format nil)
        (erase-buffer)
        (insert-image-file "202202.png"))
      (read-key)
      (delete-frame frame))


In GNU Emacs 27.1 (build 1, x86_64-apple-darwin15.3.0, X toolkit, Xaw scroll 
bars)
 of 2020-12-12 built on macbook
Windowing system distributor 'The X.Org Foundation', version 11.0.11502000
System Description:  Mac OS X 10.11.3

Configured using:
 'configure --prefix=/opt/local --disable-silent-rules --without-ns
 --without-dbus --without-gconf --without-libotf --without-m17n-flt
 --with-gmp --with-gnutls --with-json --with-xml2 --with-modules
 --infodir /opt/local/share/info/emacs --with-x-toolkit=lucid
 --without-xaw3d --without-imagemagick --with-xpm --with-jpeg
 --with-tiff --with-gif --with-png --with-lcms2 --without-rsvg
 --with-xft 'CFLAGS=-pipe -Os -arch x86_64'
 CPPFLAGS=-I/opt/local/include 'LDFLAGS=-L/opt/local/lib
 -Wl,-headerpad_max_install_names -lfreetype -lfontconfig -Wl,-no_pie
 -arch x86_64''

Configured features:
XPM JPEG TIFF GIF PNG GSETTINGS GLIB NOTIFY KQUEUE ACL GNUTLS LIBXML2
FREETYPE HARFBUZZ XFT ZLIB TOOLKIT_SCROLL_BARS LUCID X11 XDBE XIM
MODULES THREADS JSON PDUMPER LCMS2 GMP