From de564d38e9d8d03084c417ca141ea68372ac7eb9 Mon Sep 17 00:00:00 2001 From: raiden00pl Date: Sat, 4 Nov 2023 18:07:46 +0100 Subject: [PATCH] Documentation: migrate "Wide Font Support" from wiki link: https://cwiki.apache.org/confluence/display/NUTTX/Wide+Font+Support --- .../components/nxgraphics/nxfonts.rst | 84 +++++++++++++++++++ 1 file changed, 84 insertions(+) diff --git a/Documentation/components/nxgraphics/nxfonts.rst b/Documentation/components/nxgraphics/nxfonts.rst index 4c7095b01a..a780a65343 100644 --- a/Documentation/components/nxgraphics/nxfonts.rst +++ b/Documentation/components/nxgraphics/nxfonts.rst @@ -124,3 +124,87 @@ NXFONTS types :return: ``OK`` on success; ``ERROR`` on failure with ``errno`` set appropriately. +Wide Font Support +================= + +Question:: + + > My team is trying the nuttx graphics with chinese fonts, but nx seems not + > support fonts quantity more than 256 chars, right? + +Answer:: + + NuttX currently only uses fonts with 7-bit and 8-bit character sets. But + I believe that that limitation is mostly arbitrary. It should be a simple + extension to the font subsystem to use 16-bit fonts. + +Adding 16-Bit Font support +-------------------------- + +Current 7/8-bit Font Implementation +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + +All of critical font interfaces allow for 16-bit character sets: + +.. code-block:: C + + FAR const struct nx_fontbitmap_s *nxf_getbitmap(NXHANDLE handle, uint16_t ch) + +The character code is only used to look-up of a glyph in a table. There is a +definition that controls the width of the character set: CONFIG_NXFONTS_CHARBITS. +This currently defaults to 7 but all existing fonts support 8-bits. + +My first guess is that the only thing that would have to change is that single +file nxfonts_bitmaps.c (and the function nxf_getglyphset() in the file +nxfonts_getfont.c) . nxfonts_bitmaps.c is used to auto-generate 7/8-bit font +data sents. Here is how that works: + +* Each 7-8 bit file is described by a header file like, for example, + nxfonts_sans17x22.h. + +* At build time each of these header files is used to create a C file, + like, nxfonts_bitmaps_sans17x22.c. + +* It creates the C file (like nxfonts_bitmaps_sans17x22.c) by compiling + nxfonts_bitmaps.c and including nxfonts_sans17x22.h to create the font + dataset at build time. + +The function nxf_getglyphset() in the file nxfonts_getfont.c selects the 7-bit +font range (codes < 128) or the 8-bit range (code >= 128 > 256). The fonts are +kept in simple arrays splitting the data up into ranges of values lets you above +the non-printable codes at the beginning and end of each range. There is even a +comment in the code there "Someday, perhaps 16-bit fonts will go here". + +Adding Wide Fonts +~~~~~~~~~~~~~~~~~ + +To add a single wide font, the easiest way would be to simply add the final +.C file without going through the C auto-generation step. That should be VERY +easy. (But since it has never been used with larger character sets, I am sure +that there are bugs and things that need to be fixed). + +If you want to add many wide fonts, then perhaps you would have to create a new +version of the C auto-generation logic. That would require more effort. + +I am willing to help and advise. Having good wide character support in the NuttX +graphics would be an important improvement to NuttX. This is not a lot of code +nor is it very difficult code so you should not let it be an obstacle for you. + +Font Storage Issues +------------------- + +One potential problem may be the amount of memory required by fonts with +thousands of characters. If you have a lot of flash, it may not be a problem, +but on many microcontrollers it will be quite limiting. + +Options are: + +* **Font Compression** Addition of some font compression algorithm in NuttX. + However, Chinese character bitmaps do not compress well: Many of them contain + so much data that there is not much of anything to compress. Some actually + expand under certain compression algorithms. + +* **Mass Storage** A better option would be put the wide the fonts in file + system, in NAND or serial FLASH or on an SD card. In this case, additional + logic would be required to (1) format a font binary file and to (2) access + the font binary from the file system as needed.