code.py

# SPDX-FileCopyrightText: 2017 Limor Fried for Adafruit Industries
#
# SPDX-License-Identifier: MIT
# Dotstar POV Display! Can handle up to ~2300 pixel size image (e.g. 36 x 64)

import gc
import time
from adafruit_motorkit import MotorKit
import board
import busio
import digitalio

kit = MotorKit(i2c=board.I2C())

FILENAME = "nyan-xmas.bmp"
IMAGE_DELAY = 0.001
REPEAT = True
BRIGHTNESS = 0.3
PIXEL_DELAY = 0.003

dotstar = busio.SPI(board.SCK, board.MOSI)
while not dotstar.try_lock():
    pass
dotstar.configure(baudrate=44000000)

# we'll resize this later
databuf = bytearray(0)

led = digitalio.DigitalInOut(board.D13)
led.switch_to_output()

def read_le(s):
    # as of this writting, int.from_bytes does not have LE support, DIY!
    result = 0
    shift = 0
    for byte in bytearray(s):
        result += byte << shift
        shift += 8
    return result

class BMPError(Exception):
    pass

try:
    with open("/" + FILENAME, "rb") as f:
        print("File opened")
        if f.read(2) != b'BM':  # check signature
            raise BMPError("Not BitMap file")

        bmpFileSize = read_le(f.read(4))
        f.read(4)  # Read & ignore creator bytes

        bmpImageoffset = read_le(f.read(4))  # Start of image data
        headerSize = read_le(f.read(4))
        bmpWidth = read_le(f.read(4))
        bmpHeight = read_le(f.read(4))
        flip = True

        print("Size: %d\nImage offset: %d\nHeader size: %d" %
              (bmpFileSize, bmpImageoffset, headerSize))
        print("Width: %d\nHeight: %d" % (bmpWidth, bmpHeight))

        if read_le(f.read(2)) != 1:
            raise BMPError("Not singleplane")
        bmpDepth = read_le(f.read(2))  # bits per pixel
        print("Bit depth: %d" % (bmpDepth))
        if bmpDepth != 24:
            raise BMPError("Not 24-bit")
        if read_le(f.read(2)) != 0:
            raise BMPError("Compressed file")

        print("Image OK!")

        rowSize = (bmpWidth * 3 + 3) & ~3  # 32-bit line boundary

        # its huge! but its also fast :)
        databuf = bytearray(bmpWidth * bmpHeight * 4)

        for row in range(bmpHeight):  # For each scanline...
            if flip:  # Bitmap is stored bottom-to-top order (normal BMP)
                pos = bmpImageoffset + (bmpHeight - 1 - row) * rowSize
            else:  # Bitmap is stored top-to-bottom
                pos = bmpImageoffset + row * rowSize

            # print ("seek to %d" % pos)
            f.seek(pos)
            for col in range(bmpWidth):
                b, g, r = bytearray(f.read(3))  # BMP files store RGB in BGR
                # front load brightness, gamma and reordering here!
                order = [b, g, r]
                idx = (col * bmpHeight + (bmpHeight - row - 1)) * 4
                databuf[idx] = 0xFF  # first byte is 'brightness'
                idx += 1
                for color in order:
                    databuf[idx] = int(
                        pow((color * BRIGHTNESS) / 255, 2.7) * 255 + 0.5)
                    idx += 1

except BMPError as e:
    print("Failed to parse BMP: " + e.args[0])

gc.collect()
print(gc.mem_free())
print("Ready to go!")

kit.motor1.throttle = 1

while True:
    print("Draw!")
    index = 0

    for col in range(bmpWidth):
        row = databuf[index:index + bmpHeight * 4]
        dotstar.write(bytearray([0x00, 0x00, 0x00, 0x00]))
        dotstar.write(row)
        dotstar.write(bytearray([0x00, 0x00, 0x00, 0x00]))
        index += bmpHeight * 4
        time.sleep(PIXEL_DELAY)

    # clear it out
    dotstar.write(bytearray([0x00, 0x00, 0x00, 0x00]))
    for r in range(bmpHeight * 5):
        dotstar.write(bytearray([0xFF, 0x00, 0x00, 0x00]))
    dotstar.write(bytearray([0xff, 0xff, 0xff, 0xff]))
    gc.collect()

    if not REPEAT:
        break

    time.sleep(IMAGE_DELAY)