Add c_to_python_font.py.

icon_fonts/README.md

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+# Icon Fonts
+
+It is possible to display icons by incorporating their images in a font file.
+There are `.ttf` and `.otf` files available which can be converted to Python
+using `font_to_py.py`. I have not had much success with these. I also wanted
+to create my own icons. I also experimented with using a font editor to modify
+an existing font. I found the font editor unintuitive and hard to use.
+
+The solution offered here uses the Linux `bitmap` editor plus a utility to
+convert a set of its output files to a Python font file. The image below shows
+typical usage.
+
+![Image](./icon_font.jpg)
+
+# The bitmap editor
+
+This is documented in the man pages, but it is easy and intuitive to use. To
+generate (say) 19x19 icons, issue
+```bash
+$ bitmap -size 19x19
+```
+Save each bitmap under a different name: I use a `.c` extension as they are C
+source files.
+
+You need to create an additional icon to provide the output under error
+conditions, i.e. if an attempt is made to display a glyph not in the font.
+
+# The file list
+
+Create a text file listing the bitmap filenames, one filename per line. The
+icon to be used as the default (error) image should be first. Subsequent icons
+will be assigned to characters "A", "B", "C"...
+
+# Creating the Python font
+
+Assuming a file list `my_file_list.txt`, the following will create
+`my_font.py`. It requires Python 3.8 or later. The `font_to_py.py` file should
+be in the same directory.
+
+```bash
+$ ./c_to_python_font.py my_file_list.txt my_font.py
+```
+
+# Using the font
+
+The following will print `icon[2]` where `icon[0]` is the default and `icon[1]`
+is associated with "A".
+```python
+# Instantiate the ssd display object
+import my_font
+import CWriter
+wri = CWriter(ssd, my_font)
+wri.printstring("B")
+```