Something completely different now: wanting to define a font for clock output on a 22x7 pixel display. Go for a 4x7 number font as this will leave enough room for a colon in e.g. 12:34. Turns out to be tricky to generate a font map, but eventually made something, after iterating on it for a while.
4x7 is a nice arrangement as you can pack all the data for a character into a uint32_t: treating each row of the character as a nibble you get:
font = {
0: 0x69BD996,
1: 0x2622222,
2: 0x691248F,
3: 0x6912196,
4: 0x359F111,
5: 0xF886196,
6: 0x698E996,
7: 0xF112222,
8: 0x6996996,
9: 0x6997196,
}
In the actual implementation there are some details to do with byte swaps (because pushing bits out of SPI) which will be discussed once the clock code is done, but in the meantime here is the code used to render some pictures:
import array
# 8 rows of 4 bytes
pixels = array.array("I", [0, 0, 0, 0, 0, 0, 0, 0])
def display(pixels):
for j in range(8):
print(("{0:032b}".format(pixels[j])).replace("0", " ").replace("1", "■"))
font = {
0: 0x69BD996,
1: 0x2622222,
2: 0x691248F,
3: 0x6912196,
4: 0x359F111,
5: 0xF886196,
6: 0x698E996,
7: 0xF112222,
8: 0x6996996,
9: 0x6997196,
}
def render(number):
digits = list(map(int, reversed(str(number))))
for r in range(7):
row = 0
for j, d in enumerate(digits):
o = (0, 5, 12, 17)[j]
row = row | ((font[d] >> (4 * (6 - r))) & 0xF) << o
if r in (2, 4):
row |= 1 << 10
pixels[r + 1] = row
display(pixels)
for now in 1234, 2356, 908:
render(now)
The example font looks like:
■ ■■ ■■ ■■
■■ ■ ■ ■ ■ ■ ■
■ ■ ■ ■ ■ ■
■ ■ ■ ■■■■
■ ■ ■ ■ ■
■ ■ ■ ■ ■
■ ■■■■ ■■ ■
■■ ■■ ■■■■ ■■
■ ■ ■ ■ ■ ■ ■
■ ■ ■ ■ ■
■ ■ ■■ ■■■
■ ■ ■ ■ ■ ■
■ ■ ■ ■ ■ ■ ■
■■■■ ■■ ■■ ■■
■■ ■■ ■■
■ ■ ■ ■ ■ ■
■ ■ ■ ■ ■■ ■ ■
■■■ ■■ ■ ■■
■ ■ ■ ■ ■ ■
■ ■ ■ ■ ■ ■
■■ ■■ ■■
I am quite happy with this.