ColorConverter.convert() returns different values from same input

[FoamyGuy]

CircuitPython version

Adafruit CircuitPython 8.0.2 on 2023-02-14; Adafruit Feather ESP32-S2 TFT with ESP32S2
Board ID:adafruit_feather_esp32s2_tft

Adafruit CircuitPython 8.0.2 on 2023-02-14; Adafruit Feather RP2040 with rp2040
Board ID:adafruit_feather_rp2040

Code/REPL

import time
from displayio import ColorConverter, Colorspace

cc_888 = ColorConverter(input_colorspace=Colorspace.RGB888, dither=False)

results_histo = {}
for i in range(1100):
    val = cc_888.convert(0xff0000)
    if val not in results_histo:
        print(f"{i}: {hex(val)} | {val} | {bin(val)}")
        results_histo[val] = 1
    else:
        results_histo[val] += 1

        # enabling or disabling the print influences the 'failure' rate
        print(f"{i}: {hex(val)} | {val} | {bin(val)}")

print("------------")
print(results_histo)

Behavior

With the code above I would expect to receive the same result value back for every call to ColorConverter.convert() because we always input the exact same value to it's argument. But in reality sometimes we are getting a different value returned from convert() sometimes. Here is a sample of the output after 1100 iterations:

{248: 1061, 63488: 39}

So the vast majority of the time it is the same, but occasionally different. The Feather ESP32-S2 TFT seems to have an overall higher rate of differing values. With print enabled I was seeing closer to 60/40 split between the differing values. The Feather RP2040 seems like it's somewhat less likely, more often being around 50ish out of 1100 different.

Description

No response

Additional information

@gamblor21 and I discussed on discord a bit and he found a potential cause and solution. Will make a PR with that after some more testing.

I tested this on a PyPortal Titano as well and it did not seem to exhibit the same behavior. I was getting the same value returned every iteration on that device.

[gamblor21]

PR will be submitted soon but the problem was in shared-bindings/displayio/ColorConverter.c in displayio_colorconverter_obj_convert(...)

    _displayio_colorspace_t colorspace;
    colorspace.depth = 16;

The colorspace object is never initialized and later in the code colorspace.reverse_bytes_in_word is referenced. If it is incorrectly set to non-zero the function fails.

[FoamyGuy]

resolved by #7611