The GE keeps the specular and spot exponents to 5 significant bits,
truncated, and from 512 up (infinity and NaN included) uses 496. Only
the specular one was truncated, and neither saturated. A huge or NaN
exponent overflowed pspPow's bits: highlights wrong on every backend,
and on D3D11, where the overflowing float to int conversion gives a
NaN, black (Everybody's Golf, #22418). With the exponent clamped, t
stays in range for every base the backends produce.
Measured, now bit exact in the software renderer and within 4 levels
on Vulkan.
Fixes#22418
Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>
Read as an integer, a float's bits are its log2 with the mantissa a
straight line between powers of two, scaled by 2^23, and writing an
integer back is the matching exp2. That's exactly the GE's
approximation, without log2/exp2/floor. pspPow now also returns 1 for
e <= 0 itself, so the callers drop their checks. Shader languages
without integers fall back to a true pow.
Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>
The viewer is at infinity along view space +z, so in world space, where
lighting happens, it's the view matrix's third column rather than
(0,0,1): turning the camera moves the highlights (gpu/lighting/specular).
The shaders read it from u_view.
In a Need for Speed Carbon frame replayed on a PSP, this and the pow
bring the error of the cars from MSE 957 to 120 (Vulkan).
Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>
The shaders and the software renderer only add specular when N.L >= 0,
as the GE does (gpu/lighting/specular); the CPU lighter, used for points,
lines and rectangles, didn't check.
Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>
The GE computes these powers as exp2(e * log2(x)), with log2 and exp2
each a straight line between powers of two (Mitchell's approximation),
and only uses the top 4 bits of the specular coefficient's mantissa.
Through a highlight's falloff a true pow is 10-30 steps of 255 brighter
at the exponents games use. Measured in gpu/lighting/specular.
Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>
