Font Converter for efficient drawing on SH1106-ish OLED screens. Generates header files. No known character size limitations, although the per-character byte-length header is only 16-bits wide.
Usage: bfd_to_oled.rb [options]
-v, --[no-]verbose Run verbosely
-h, --header Include Header
-s, --single-line
-t, --typedef Include Typedef
-r, --range RANGE Character range to print, fmt 'a-b'
-n, --name NAME Name (identifier) of font (probably should be camel-case)
This code is not well-tested, but it does work for me.
Used as part of a build script to generate appropriate bitmap fonts for use on an oled screen. The screen is arranged in vertical 8-bit pages starting on the top-left. The next byte is vertical and directly to the right. After reaching the right limit of the first 8-bit tall "row", the page increments and the column resets.
// 006D: 'm' (6d, 180 bytes)
// box: 45 30
// offset: 22249
// 0123456789abcdef....
// 1-0----------##------------------------------------
// 1---------###------------------------------------
// 2-------#####------------------------------------
// 3----########------#####---------######----------
// 4############----#########-----##########--------
// 5############---###########---###########--------
// 6-----########-############--#############-------
// 7------#########----##########----########-------
// 2-0------########------########------########------
// 1------########-------#######-------#######------
// 2-------######--------######--------#######------
// 3-------######--------######--------#######------
// 4-------######--------######--------#######------
// 5-------######--------######--------#######------
// 6-------######--------######--------#######------
// 7-------######--------######--------#######------
// 3-0-------######--------######--------#######------
// 1-------######--------######--------#######------
// 2--------#####-------#######--------#######------
// 3--------#####-------#######--------######-------
// 4--------#####------########-------#######-------
// 5--------#####----###########------#######-------
// 6-------######-----------######--#########-------
// 7------########-----------------##########-------
// 4-0--#############------------------#########------
// 1--#################-----------------######------
// 2--------------------------------------####------
// 3----------------------------------------###-----
// 4-----------------------------------------####---
// 5-------------------------------------------##---
Characters are variably sized. The first three bytes of each character are a header consisting of
the pixel width (bbx) and bytesize (a uint16_t as two bytes, MSB). So how do you find an individual
character? A lookup table is generated showing the offset of each character starting with the first,
which is specified by the --range option.
const font_t bebas_big = {
.data = _bebas_big_data,
.startchar = ' ',
.length = 94,
.lookup = {0x00, 0x03, 0x30, ... },
};
The generator creates files based on this typedef:
typedef struct {
const uint8_t * data;
char startchar;
uint8_t length;
int16_t lookup[];
} font_t;
Pointers to const font_t can be passed around to drawing routines:
uint8_t charnum = c - font->startchar; // If the font starts with 'A', change 'A' to 0, for the 0th char
int offset = font->lookup[charnum]; // Get the offset into the font table
const uint8_t * glyph = &font->data[offset]; // Get the glyph data, starting with width and byte length
uint8_t width = *glyph++;
uint16_t bytelen = *glyph++ << 8;
bytelen |= *glyph++;
uint8_t pages = bytelen / width;
From there you can dump it into your screen buffer however you see fit.
It's useful to create a build script that will auto-generate fonts from, say OTF files (use otf2bfd) that can then be used from a makefile. An example is included.