More Fonts

Are you looking to display new fonts on your PyPortal? You can use just about any font on your computer or downloaded from the internet. This guide will walk you through generating bitmap fonts using the FontForge open-source project.

Why Bitmaps?

PyPortal uses the CircuitPython Bitmap Font Library to render "live" text on the display. A bitmap font stores each character as an array of pixels. Bitmap fonts are simply groups of images. For each variant of the font, there is a complete set of images, with each set containing an image for each character.

Computers, on the other hand, use variable size 'TrueType' or 'Postscript' fonts, where there's a mathematical algorithm that defines each character, so it can be drawn at any size.

Font Forging

This is where FontForge comes into play. FontForge is an open-source font editor for Windows, Mac OS and GNU+Linux. It features tools for converting existing fonts into different font formats.

Getting Started with FontForge

Head on over to the fontforge page and download the app for your platform. You can choose to donate, subscribe via email or simply click the "Subscribe/Confirm and Download" button (no need to enter an email).  Follow along with the detailed installation guide to get setup with FontForge.

Where Do I Get Fonts?

Here's a list of some neat places to obtain some fresh fonts.

Demo Walkthrough

In this example, we're going to convert a .TTF (TrueType Format) into a .BDF (Bitmap Distribution Format). I'm using an open licensed font downloaded from Google Font, Source Serif Pro

Open Font

Use the file menu and choose Open Font from the list. Navigate to a directory where your desired font resides. Select the font and open it.

Set Font Size

From the element menu, select Bitmap Strikes Available. In this dialog, you will need to specific how large you want your font to be. The font size is fixed with Bitmap fonts, so if you want to use different sizes, you'll need to make separate files.

Generate Bits

From the element menu, select Generate Bitmap. Similar to the previous dialog, enter the font size of your liking. You can make it smaller here. Be aware, values too small will not generate BDF's. 

Export Converted Font

From the file menu, select Generate Fonts. In the dialog, select No Outline Font and BDF from the dropdown options. Use the navigation UI to save the file in your directory of choice. Click the generate button to save the file. 

BDF Resolution

This dialog menu will pop up after clicking generate. You can choose one of the options from the list. If you'd like a different font size, you can enter that in the Other labeled input box. Click OK to save it!

Optimize File Size

If you take a look at the file size of the .bdf, it's roughly around 900K – That can be a bit larger than needed, especially if you plan to store a lot of image and sound assets. In cases where you need to save on every byte, you can optimize the file size of your fonts by selecting only the characters you want to use. If you scroll through the full list of glyphs, you'll see there's extra special characters – A whole bunch of them! If you don't need them in your project, just select "space" (the glyph just before "!") plus the basic set of upper/lower and alphanumeric characters. You can click + hold and drag to make selections easier. With them selected, go through these steps:

  1. Select the glyphs you want to keep
  2. Use Edit→Select→Invert Selection to change the selection to the unwanted glyphs.
  3. Use Encoding→Detach & Remove Glyphs... to remove the unwanted glyphs. (You'll have to re-load your original font file to undo this step)
  4. Use Element→Regenerate Bitmap to reprocess the glyphs.
  5. Use File→Generate Font to save the reduced version of the file
Make sure your font contains the letter capital M

Make sure your final font contains the letter capital M, which is used to estimate the height of letters in the font. Otherwise, the font will be incompatible with adafruit_display_text and give an error like AttributeError: 'NoneType' object has no attribute 'height'

Optimize File Size (Manually)

If you prefer, you can also use a text editor to remove glyphs from a .bdf file. BDF files are just text!

Open a BDF file and search for “asciitilde” — this is usually the highest plain-ASCII-value glyph we want to preserve. A few lines down there will be an “ENDCHAR” line.

Delete everything after the ENDCHAR line, then add a line containing ENDFONT. That’s it! Save the file, which is usually just a small fraction of the original size.

You won’t get any accented characters or special punctuation this way, so it’s not always the right thing for every situation. For the majority of plain-text programs though, this can really help stretch your CIRCUITPY drive space!

Font Colors

The color of the fonts can be setup in your code. The CircuitPython library uses HEX color codes. This is similar to web color pickers but formatted slightly different. Most HEX color pickers use a hashtag in the front of the value, like, #000000. In CircuitPython, instead of a hashtag, 0x is used. Here's a few examples.

  • Black =  0x000000
  • White = 0xFFFFFF
  • Purple = 0x8f42f4

CircuitPython supports two font formats: the textual .bdf format and the binary .pcf format. By taking the extra step of converting your font to .pcf you make fonts load faster and also typically save some storage space on the board CIRCUITPY flash drive.

The converter software is hosted on github.io. Thanks to technology called emscripten, it runs entirely in your web browser—the font file is not uploaded to a server, which also makes it really quick. web-bdftopcf is derived from the classic font converter of the same name, a program for Unix/Linux systems. If you're interested, you can browse the C source on github.

Head to https://adafruit.github.io/web-bdftopcf/ and click the "Browse" button.

Select a .bdf file from your computer and click Open.

After a moment, the font will be prepared in .pcf format and depending on your browser settings it may be automatically downloaded or you may have to confirm that you want to download the file.

In this particular case, the .pcf version of the font is only half the size of the .bdf font, which leaves more space on the CIRCUITPY drive for other assets like sound files and bitmaps.

This guide was first published on Feb 18, 2019. It was last updated on Feb 18, 2019.