Memoryview copy to Displayio.Bitmap not working for most display widths

[RetiredWizard]

CircuitPython version

Adafruit CircuitPython 9.2.0-beta.0-35-g6f6b8b03a6 on 2024-10-09; ESP32-S3-DevKitC-1-N8R8-with-HACKTABLET with ESP32S3
Adafruit CircuitPython 9.2.0-beta.0-31-g14d3f2e839 on 2024-10-08; Raspberry Pi Pico 2 with rp2350a (using dvi sock)

Code/REPL

import displayio

databytes = bytearray(64)
for i in range(64):
    databytes[i] = i+1

for i in range(2,64):
    bitmap = displayio.Bitmap(i,i,255)
    mem = memoryview(bitmap)
    mem[i:i+i] = databytes[0:i]
    
    passed = 0
    for j in range(i):
        if bitmap[j,1] != databytes[j]:
            passed += 1
            
    if passed == 0:
        print(f'memoryview copy for bitmap dimension of {i} passed')

Behavior

memoryview copy for bitmap dimension of 4 passed
memoryview copy for bitmap dimension of 8 passed
memoryview copy for bitmap dimension of 12 passed
memoryview copy for bitmap dimension of 16 passed
memoryview copy for bitmap dimension of 20 passed
memoryview copy for bitmap dimension of 24 passed
memoryview copy for bitmap dimension of 28 passed
memoryview copy for bitmap dimension of 32 passed
memoryview copy for bitmap dimension of 36 passed
memoryview copy for bitmap dimension of 40 passed
memoryview copy for bitmap dimension of 44 passed
memoryview copy for bitmap dimension of 48 passed
memoryview copy for bitmap dimension of 52 passed
memoryview copy for bitmap dimension of 56 passed
memoryview copy for bitmap dimension of 60 passed

Description

The memoryview copy into the second line of the bitmap matrix gets corrupted for any bitmap with a width which isn't an even multiple of 4. This is causing image display issues in the adafruit_imageload library as discussed in adafruit/Adafruit_CircuitPython_ImageLoad#88

Additional information

Running the following with values of 8 and 10 shows a working and a corrupted matrix:

import displayio

databytes = bytearray(100)
for i in range(100):
    databytes[i] = i+1
dm = 8
bitmap = displayio.Bitmap(dm,dm,255)
mem = memoryview(bitmap)

print('Memoryview copies into bitmap of width',dm)

for i in range(dm):
    mem[dm*i:(dm*i)+dm] = databytes[dm*i:(dm*i)+dm]

    for j in range(dm):
        print(f'{bitmap[j,i]}:',end="")
    print()

Memoryview copies into bitmap of width 8
1:2:3:4:5:6:7:8:
9:10:11:12:13:14:15:16:
17:18:19:20:21:22:23:24:
25:26:27:28:29:30:31:32:
33:34:35:36:37:38:39:40:
41:42:43:44:45:46:47:48:
49:50:51:52:53:54:55:56:
57:58:59:60:61:62:63:64:

Memoryview copies into bitmap of width 10
1:2:3:4:5:6:7:8:9:10:
13:14:15:16:17:18:19:20:0:0:
25:26:27:28:29:30:0:0:0:0:
37:38:39:40:0:0:0:0:0:0:
49:50:0:0:0:0:0:0:0:0:
0:0:0:0:0:0:0:0:0:0:
0:0:0:0:0:0:0:0:0:0:
0:0:0:0:0:0:0:0:0:0:
0:0:0:0:0:0:0:0:0:0:
0:0:0:0:0:0:0:0:0:0:

[RetiredWizard]

Modifying the Matrix dump routine so it performs all the copies first and then dumps the matrix, results in the following:

Memoryview copies into bitmap of width 10
1:2:3:4:5:6:7:8:9:10:
13:14:15:16:17:18:19:20:21:22:
25:26:27:28:29:30:31:32:33:34:
37:38:39:40:41:42:43:44:45:46:
49:50:51:52:53:54:55:56:57:58:
61:62:63:64:65:66:67:68:69:70:
73:74:75:76:77:78:79:80:81:82:
85:86:87:88:89:90:91:92:93:94:
97:98:99:100:0:0:0:0:0:0:
0:0:0:0:0:0:0:0:0:0:

[RetiredWizard]

I think I tracked down my issue. It looks like Displayio fills each bitmap row to end at an even 4 byte boundary. So when using memoryview to copy data into the bitmap, you need to adjust the destination after each row by any filler space.

There still seems to be an issue using memoryview for bitmaps with a color depth of 4 or less. If I can't figure that out it may warrant a separate issue.