`navigtion.ttf` is created with the web app [icomoon](https://icomoon.io/app) by importing the svg files from `src/displayapp/icons/navigation/unique` and generating the font. `lv_font_navi_80.json` is a project file for the site, which you can import to add or remove icons.
To save space in the internal flash memory, the navigation icons are now moved into the external flash memory. To do this, the TTF font is converted into pictures (1 for each symbol). Those pictures are then concatenated into 2 big pictures (we need two files since LVGL supports maximum 2048px width/height). At runtime, a map is used to locate the desired icon in the corresponding file at a specific offset.
Here is the command to convert the TTF font in PNG picture:
```shell
convert -background none -fill white -font navigation.ttf -pointsize 80 -gravity center label:"\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n" navigation0.png
convert -background none -fill white -font navigation.ttf -pointsize 80 -gravity center label:"\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n" navigation1.png
```
*Please note that the characters after `label:` are UTF-8 characters and might not be displayed correctly in this document.*
The characters in the TTF font range from `0xEEA480` to `0xEEA4A9`. Characters from `0xEEA480` to `0xEEA498` are stored in `navigation0.png` and the others in `navigation1.png`. Each character is 80px height so displaying a specific character consists in multiplying its index in the file by -80 and use this value as the offset when calling `lv_img_set_offset_y()`.
