Progress on a Game

Published on 2018-01-20 in Micro:Boy.

With the hardware finalized, the remaining work is to actually write at least one game, to prove that it’s possible. I decided to make a game inspired by such classics as Dig Dug, Digger and Boulder Dash — you dig tunnels, collect gems, avoid monsters and drop boulders on them. So far I have the basic graphics and the player animation:

———- more ———-The code for the display got a bit simplified, and merged with the code for buttons. I also added a “tick” function for keeping a constant frame rate.

import microbit


DIRT = b'\x8a \x05P\x05 \x8a '
DARK = b'\x00\x00\x00\x00\x00\x00\x00\x00'
ROCK_MASK = b'<~\xff\xff\xff\xff~<'
ROCK = b'\x004Z>V*\x14\x00'
GEM = b'\x00\x18,N\x02\x04\x08\x00'
MAN_MASK = b'0\xfe\xff\xff\xff\xff\xfe0'
MAN = (b'\x00\x10z>:~ \x00', b'\x00 \x1a~z>\x10\x00')


class Console:
    _command = bytearray(b'\x00\xb0\x02\x10')

    def __init__(self):
        self.next_frame = microbit.running_time() + 100
        self.buffer = bytearray(1024)
        self.dirty_min = bytearray([0] * 8)
        self.dirty_max = bytearray([128] * 8)
        microbit.i2c.init(freq=400000, scl=microbit.pin2, sda=microbit.pin1)
        try:
            microbit.i2c.write(0x3c, b'')
        except OSError:
            pass
        _init = (b'\x00\xae\xd5\x80\xa8\x3f\xd3\x00\x40\x80\x14'
                 b'\x20\x00\xa1\xc8\xa1\xda\x12\x81\xcf\xd9\xf1'
                 b'\xdb\x40\xa4\xa6\xaf')
        microbit.i2c.write(0x3c, _init)

    @staticmethod
    def buttons():
        return microbit.i2c.read(0x10, 1)[0]

    def tick(self, ms=100):
        delay = self.next_frame - microbit.running_time()
        if delay > 0:
            microbit.sleep(delay)
        self.next_frame += ms

    def update(self):
        buf = self.buffer
        index = 0
        for page in range(8):
            dmin = self.dirty_min[page]
            dmax = self.dirty_max[page]
            if dmax:
                self._command[1] = 0xb0 | page
                self._command[2] = 0x00 | ((2 + dmin) & 0x0f)
                self._command[3] = 0x10 | ((2 + dmin) >> 4) & 0x0f
                microbit.i2c.write(0x3c, self._command)
                microbit.i2c.write(0x3c,
                                   b'\x40' + buf[index + dmin:index + dmax])
            index += 128
            self.dirty_max[page] = 0
            self.dirty_min[page] = 127

    def blit(self, x, y, data, mask=b''):
        if not -8 < x < 128:
            return
        if x < 0:
            data = data[-x:]
            x = 0
        elif x > 120:
            data = data[:120 - x]
        page = y // 8
        shift = y % 8
        if 0 <= page <= 7:
            index = x + 128 * page
            for byte in mask:
                self.buffer[index] &= ~(byte << shift)
                index += 1
            index = x + 128 * page
            for byte in data:
                self.buffer[index] ^= byte << shift
                index += 1
            self.dirty_min[page] = min(self.dirty_min[page], x)
            self.dirty_max[page] = max(self.dirty_max[page], x + 8)
        page += 1
        if 0 <= page <= 7 and shift:
            shift = 8 - shift
            index = x + 128 * page
            for byte in mask:
                self.buffer[index] &= ~(byte >> shift)
                index += 1
            index = x + 128 * page
            for byte in data:
                self.buffer[index] ^= byte >> shift
                index += 1
            self.dirty_min[page] = min(self.dirty_min[page], x)
            self.dirty_max[page] = max(self.dirty_max[page], x + 8)


console = Console()
for y in range(8):
    for x in range(16):
        if (x + 3 * y + 1) % 5:
            console.blit(x * 8, y * 8, DIRT)
console.blit(0, 0, ROCK, ROCK_MASK)
console.blit(0, 16, GEM, ROCK_MASK)
frame = 0
facing = 1
x = 0
y = 8
while True:
    frame = (frame + 1) % 4
    buttons = console.buttons()
    if buttons & 4:
        x += 1
        facing = 1
    elif buttons & 16:
        x -= 1
        facing = -1
    man = MAN[frame // 2]
    if facing > 0:
        man = reversed(man)
    console.blit(x, y, man, MAN_MASK)
    console.update()
    console.blit(x, y, DARK, MAN_MASK)
    console.tick(50)

You can also see how you can easily mirror the sprites by calling “reversed” on their data.