bug#25863: 25.1; garbage display by small image

[ynyaaa]

Eli Zaretskii <eliz@gnu.org> writes:
> I'm not sure I understand how to change the test case to account for
> the above.  Evaluating "(face-font 'default)" in "emacs -Q" produces
> this:
>
>   "-outline-Courier New-normal-normal-normal-mono-13-*-*-*-c-*-iso8859-1"
>
> How to change the test case to reproduce the problem with this font,
> please?

Starting emacs -Q and (set-frame-font
"-outline-Courier New-normal-normal-normal-mono-13-*-*-*-c-*-iso8859-1"),
the form below displayed garbage.
The value for 'h' may be modified between 9 and 16.

(let ((h 16))
  (switch-to-buffer (generate-new-buffer "temp"))
  (insert-image (create-image (concat (format "P4\n8 %d\n" h)
                                      (make-string h 127))
                              'pbm t))
  (insert ?g)
  (redisplay)
  (delete-char -1))

The attached image is the screen shot of the garbage display.
The left rectangle is the pbm image and the right rectangle
is text cursor, which looks shorter than the line height
where the line height equals to the image height.

test-emacs-garbage.png
Description: PNG image