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BPMemory: Handle fog configuration where both A and C are infinity/NaN

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The console appears to behave against standard IEEE754 specification
here, in particular around how NaNs are handled. NaNs appear to have no
effect on the result, and are treated the same as positive or negative
infinity, based on the sign bit.

However, when the result would be NaN (inf - inf, or (-inf) - (-inf)),
this results in a completely fogged color, or unfogged color
respectively. We handle this by returning a constant zero for the A
varaible, and positive or negative infinity for C depending on the sign
bits of the A and C registers. This ensures that no NaN value is passed
to the GPU in the first place, and that the result of the fog
calculation cannot be NaN.
This commit is contained in:
Stenzek
2018-02-01 17:36:30 +10:00
parent 1264daae9b
commit 260d5b7aa7
4 changed files with 54 additions and 21 deletions
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21
Source/Core/VideoCommon/BPMemory.h
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@ -654,14 +654,9 @@ union BlendMode
union FogParam0
{
struct
{
u32 mantissa : 11;
u32 exponent : 8;
u32 sign : 1;
};
float GetA() const;
BitField<0, 11, u32> mant;
BitField<11, 8, u32> exp;
BitField<19, 1, u32> sign;
u32 hex;
};
@ -675,9 +670,6 @@ union FogParam3
BitField<21, 3, u32> fsel; // 0 - off, 2 - linear, 4 - exp, 5 - exp2, 6 -
// backward exp, 7 - backward exp2
// amount to subtract from eyespacez after range adjustment
float GetC() const;
u32 hex;
};
@ -721,6 +713,13 @@ struct FogParams
};
FogColor color; // 0:b 8:g 16:r - nice!
// Special case where a and c are infinite and the sign matches, resulting in a result of NaN.
bool IsNaNCase() const;
float GetA() const;
// amount to subtract from eyespacez after range adjustment
float GetC() const;
};
union ZMode