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1.8 KiB
1.8 KiB
FTDI EVE Unicode Rendering
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The FTDI EVE chips have several fonts in ROM, but these fonts only contain a
subset of ASCII characters. Notably, this excludes diacritics and accents
used in most Western languages.
While the FTDI EVE has the capability for user-defined fonts, such fonts only
support 127 character positions, making them as limiting as the built-in fonts.
As a further complication, high resolution TFT displays require high resolution
fonts. It is not feasible to put a complete international font into the limited
flash memory of most microprocessors.
To work around these limitations, this library uses a custom font renderer with
the following characteristics:
1) Rather than providing bitmaps for different font sizes, it uses a single
bitmap for the largest font size (romfont 31) and emulates other sizes by
scaling the bitmaps using BITMAP_TRANSFORM.
2) Rather than loading an entire font, it combines symbols from romfont 31
with a limited number of symbols from a custom font. For accented letters,
the rendering code combine basic letter shapes from romfont 31 with
bitmaps containing only the accent themselves.
3) The custom bitmap is RLE compressed into PROGMEM. For accents, which have
a fairly small number of non-white pixels, the savings are significant.
These characteristics enable an alphabet for Western languages to be
synthesized from only a few dozen custom symbols and modest PROGMEM use (~10k)
The text layout is done by the code in "unicode.cpp" with the help of one of
more character renderers (e.g. "western_char_set.cpp"). Each character render
is responsible for loading the necessary bitmap data into RAMG and drawing
characters as requested.
To add symbols for other languages, it will only be necessary to make a bitmap
and implement a corresponding character renderer.