Illustrate more font problems

* etc/PROBLEMS (Runtime problems specific to Android): Mention
problems with three other fonts users have inquired into.

1 files changed, 41 insertions, 0 deletions

diff --git a/etc/PROBLEMS b/etc/PROBLEMS
index 131f8740845..c139f25e086 100644
--- a/etc/PROBLEMS
+++ b/etc/PROBLEMS
@@ -3453,6 +3453,47 @@ Then, reassemble the font from the modified XML:
 which should produce a modified font by the name of
 Anonymous_Pro#1.ttf.
 
+** The "IBM Plex Mono" font displays incorrectly.
+
+This problem is precipitated by an attempt to exploit the undocumented
+feature of the MS font scaler explicated within the previous heading.
+
+Its remedy is also unsurprisingly alike the fix described there: both
+patching the preprogram to reset the point movement vectors and
+replacing the instruction code with code generated by "ttfautohint"
+will adequately resolve the problem.
+
+** Glyphs are missing within the "Arial" font or it does not load.
+
+On account of its origins at Microsoft, instruction code included
+within this font is awash with references to behavior specific to the
+MS scaler.  It is incorrigibly broken, to a degree that even
+"ttfautohint" cannot repair; your only recourse is to select some
+other font.
+
+This issue may extend beyond Arial to encompass a larger selection of
+fonts designed by Microsoft.
+
+** Some TrueType test fonts don't work.
+
+It is unlikely that any of these fonts will really prove useful for
+text editing tasks, since they are designed for the express purpose of
+testing a TrueType font scaler.  The following explanation is present
+only to satisfy a cat-like curiosity.
+
+Most TrueType test fonts "hide" points by moving them to a
+preposterous location outside the confines of the glyph bounding box.
+The Microsoft scaler and FreeType promptly disregard such points.
+
+Nothing in the TrueType specifications implies that points "hidden" in
+this fashion should be afforded any special treatment, and thus Emacs
+eschews doing so.  Consequentially, black streaks are displayed as
+Emacs interpolates glyph edges between points within the glyph and
+points the test font attempts to hide.
+
+Since this behavior does not influence the display of real fonts, no
+action will be taken to address this problem.
+
 ** CJK text does not display in Emacs, but does in other programs.
 
 When inserting CJK text into a buffer or visiting a file containing