The scalar-constant ALU ops (MULSC/ADDSC/SUBSC, opcodes 42-47) address
their operands through src3 in a special way, not via src_a/src_b like
ordinary scalar ops:
temp reg = (src3_swiz & 0x3C) | (scalar_opc & 1), component = src3_swiz & 3
const idx = src3_reg (+256 for the PS constant bank), component = .w
The op is then temp <op> const.
We were feeding these the plain (src_a.x, src_b.x). For the movie's
YUV->RGB luma scale that made the single MULSC0 compute r0.x * r0.x = Yb^2
(a squared luma) instead of r0.x * alu[511].w = Yb * 1.1643 (the limited-
range 255/219 luma scale). The squared luma crushed shadows, so dark
regions rendered as near-pure chroma -- the intro's dark background read
purple/magenta while the bright logo looked roughly right.
With correct addressing the luma is linear: the background drops to near
black (was a purple ~(37,15,39), now ~(12,0,14)) and the logo reaches full
white -- the authentic SQUARE ENIX intro. (The earlier attempt at this
addressing failed only because the PS constant bank was still mis-indexed
before the +256 fix, so the coefficients read zero -> black.)
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
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