Misallocated Pixels when GS2HMSBFormat has a width that's not a multiple of 4

[galdam]

When the frame buffer has a width that's not a multiple of 4, pixels at the edge are misallocated.
I've put together the following as an example:

BLACK = 1
RED = 2
WHITE = 3

WIDTH = 7
HEIGHT = 2

buffer = bytearray(math.ceil((WIDTH * HEIGHT) / 4))
fb = adafruit_framebuf.FrameBuffer(
    buffer, WIDTH, HEIGHT, buf_format=adafruit_framebuf.GS2_HMSB, 
)
fb.fill(WHITE)

def print_arr(a):
   "Print the byte array as paired bytes"
    n = 2
    a = ''.join([f'{v:08b}' for v in a])
    a = [a[i:i + n] for i in range(0, len(a), n)]
    for r in range(HEIGHT):
        print(' '.join(a[r*WIDTH:(r+1)*WIDTH]))
    print(' '.join(a[(r+1)*WIDTH:]))

color_map = {3:'_', 2: '*', 1: '#'}
def print_buffer(the_fb):
    print("+" * (the_fb.width + 2))
    for y in range(the_fb.height):
        print("+", end="")
        for x in range(the_fb.width):
            c = fb.pixel(x, y)
            print(color_map[c], end="")
        print("+")
    print("+" * (the_fb.width + 2))

Using the above, setup:

fb.pixel(4,0, RED) 
print_arr(fb.buf)
print_buffer(fb)

gives

11 11 11 11 11 11 11
10 11 11 11 11 11 11
11 11

+++++++++
+____*__+
+*______+
+++++++++

The same result occurs with fb.pixel(0,1, RED) as well.

[galdam]

How about this as a solution:

class GS2HMSBFormat:

    @staticmethod
    def get_pixel(framebuf, x, y):
        """Get the color of a given pixel"""
        index = (y * framebuf.stride + x) >> 2
        pixel = framebuf.buf[index]

        # shift = (x & 0b11) << 1
        shift = ((y * framebuf.stride + x) & 0b11) << 1  # Update to use the absolute index of the pixel
        return (pixel >> shift) & 0b11