bdfconv: add characters from utf8 text file

[koendv]

The goal of this PR is to save flash by reducing a font to only those characters that are actually used.

bdfconv converts a bdf font to an u8g2 font.
This PR adds to bdfconv an option -u filename, where filename is a text file in utf8 format.
All characters in the text file are added to the created u8g2 font.
This is useful if a font contains many characters, but only few characters are used.
Examples are programs that have menus in multiple languages, or use Asian languages like Chinese.
One suggested use is generating a font from strings in firmware source files.

To add the characters in file example.txt to the default ascii set:

bdfconv -f 1 -u example.txt -n u8g2_font_unifont -o unifont.h unifont-16.0.02.bdf

Two examples where the font is megabytes in size, but the program only needs a kbyte.

example 1

Print a text in multiple languages in Arduino. Code:

void setup(void) {
  u8g2.begin();
  u8g2.enableUTF8Print();
  u8g2.clearBuffer();
  u8g2.setFont(u8g2_font_unifont);
  u8g2.setCursor(0, 15);
  u8g2.println("Hello 您好");
  u8g2.setCursor(0, 31);
  u8g2.println("Здравствуйте");
  u8g2.setCursor(0, 47);
  u8g2.println("こんにちは");
  u8g2.setCursor(0, 63);
  u8g2.println("안녕");
  u8g2.setCursor(0, 79);
  u8g2.print("font ");
  u8g2.print(sizeof(u8g2_font_unifont));
  u8g2.println(" bytes");
  u8g2.sendBuffer();
}

• Download gnu unifont in bdf format.

• Create a font that contains all of ascii, and all characters in the sketch:

bdfconv -f 1  -m '32-127' -u ~/Arduino/bdfconv_test/bdfconv_test.ino -n u8g2_font_unifont -o unifont.h unifont-16.0.02.bdf

where bdfconv_test.ino is the sketch source.

• Copy the file unifont.h to your source directory

cp unifont.h  ~/Arduino/bdfconv_test/

• Compile and run. The text appears on the display. The display is also output in PBM format on the serial port:

The font uses 1750 bytes of flash. This is 478 bytes more than same font using only the ascii set.

Arduino sketch attached.
sketch.zip

example 2

Simplified Chinese, STM32F103, SSH1306 OLED display. Code:

void setup(void) {
  int h = 16;
  u8g2.begin();
  u8g2.enableUTF8Print();
  u8g2.clearBuffer();
  u8g2.setFont(u8g2_font_puhuiti_t12);
  u8g2.setCursor(0, h - 1);
  u8g2.print("这是一个易于");
  u8g2.setCursor(0, 2 * h - 1);
  u8g2.print("操作的U8G2");
  u8g2.setCursor(0, 3 * h - 1);
  u8g2.print("字体生成工具.");
  u8g2.sendBuffer();
}

• Download Alibaba PuHuiTi font
• convert the otf font to a bdf bitmap font
  otf2bdf -p 14 -o AlibabaPuHuiTi-3-35-Thin-14.bdf AlibabaPuHuiTi-3-35-Thin.otf
• create a u8g2 font that has the Chinese characters used in the sketch
  bdfconv -f 1 -u bdfconv_test_chinese.ino -n u8g2_font_puhuiti_t14 -o u8g2_font_puhuiti_t14.h AlibabaPuHuiTi-3-35-Thin-14.bdf
  where bdfconv__test_chinese.ino is the sketch source.
• compile and run. Display:

The font uses 4156 bytes of flash. This is 591 bytes more than same font using only the ascii set.

Arduino sketch attached.
bdfconv_test_chinese.zip

[olikraus]

nice idea