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Code Issues Releases Activity

; Add tasks for the Android port

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* etc/PROBLEMS: Improve descriptions of issues with Droid Sans
Mono and Anonymous Pro.  Then, bring up the subject of CFF fonts
and how they relate to CJK text.

* etc/TODO: Detail that CFF support is desired.
This commit is contained in:
Po Lu 2023-08-17 10:03:49 +08:00
parent f38bcf37dc
commit ab8bc93cd4
2 changed files with 46 additions and 9 deletions
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42
etc/PROBLEMS
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@ -3353,7 +3353,7 @@ this and many other problems do not exist on the regular X builds.
** Text displayed in the default monospace font looks horrible.
Droid Sans Mono (the default Monospace font which comes with Android)
comes with instruction code designed for Microsoft's proprietary
incorporates instruction code designed for Microsoft's proprietary
TrueType font scaler. When this code is executed by Emacs to instruct
a glyph containing more than one component, it tries to address
"reference points" which are set to the values of two extra "phantom
@ -3398,6 +3398,11 @@ you are not seeing problems with character display, as the
automatically generated instructions result in superior display
results that are easier to read.
We have been told that the default Sans font under Android 2.3.7,
named "Droid Sans", also exhibits this problem. The procedure for
repairing the font is identical to the procedure outlined above,
albeit with "DroidSansMono" replaced by simply "DroidSans".
** The "Anonymous Pro" font displays incorrectly.
Glyph instruction code within the Anonymous Pro font relies on
@ -3407,14 +3412,15 @@ interpreter control registers after the execution of the font
pre-program, which sets them to a value that is perpendicular to the
horizontal plane of movement.
Since Emacs does not provide this "feature", various points within
Since Emacs does not provide this "feature", various points inside
glyphs are moved vertically rather than horizontally when a glyph
program later executes an "MIRP" (Move Indirect Relative Point)
instruction.
program later executes an instruction such as "MIRP" (Move Indirect
Relative Point) that moves and measures points along the axis
specified by those registers.
This can be remedied in two ways; the first (and the easiest) is to
replace its instruction code with that supplied by "ttfautohint", as
depicted above. The second is to patch the instruction code within
depicted above. The second is to patch the instruction code inside
the font itself, using the "ttx" utility:
https://fonttools.readthedocs.io/en/latest/ttx.html
@ -3435,11 +3441,10 @@ then, find the end of the section labeled 'prep':
</prep>
and insert the following instruction immediately before the closing
'/assembly' tag:
'/assembly' tag, so as to reset the interpreter control registers back
to their default values prior to the completion of the pre-program:
SVTCA[1]
(which stands for "Set Vector registers to Control Axis X")
SVTCA[1] /* Set Vector registers to Control Axis X */
Then, reassemble the font from the modified XML:
@ -3448,6 +3453,25 @@ Then, reassemble the font from the modified XML:
which should produce a modified font by the name of
Anonymous_Pro#1.ttf.
** CJK text does not display in Emacs, but does in other programs.
When inserting CJK text into a buffer or visiting a file containing
CJK text, Emacs often fails to locate a suitable font. This problem
manifests itself as hollow squares with numbers and letters within
being displayed in lieu of the text itself.
The reason for this is Emacs's absence of support for OpenType fonts
utilizing CFF (Compact Font Format) outlines, which the CJK fonts
bundled with Android have been distributed as since Android 7.0.
The solution is to install a TrueType CJK font to the user fonts
directory detailed in the "Android Fonts" node of the Emacs manual.
Introducing support for the byzantine CFF font format into the Android
port is a large undertaking that we are looking for volunteers to
perform. If you are interested in taking responsibility for this
task, please contact <emacs-devel@gnu.org>.
* Build-time problems
** Configuration

13
etc/TODO
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@ -1748,6 +1748,19 @@ The former is based on the GVFS archive backend, which makes it
available on GNU/Linux only. That implementation has further
drawbacks like it doesn't support to write into archives.
** Provide support for CFF outlines in the Android port.
The file src/sfnt.c supplies the font backend for the Android port.
It is presently a self contained TrueType scaler, implementing both a
grayscale outline generator and an instruction code interpreter.
Support for CFF (Compact Font Format) outlines will facilitate
utilizing fonts distributed as ".otf" files, a category that currently
encompasses all CJK and some Middle Eastern and Indic fonts
distributed with Android, obviating the present requirement for users
of such scripts to actively install TrueType versions of fonts
otherwise bundled with the system.
* Other known bugs
** 'make-frame' forgets unhandled parameters, at least for X11 frames