mirror of
https://github.com/dolphin-emu/dolphin.git
synced 2024-09-21 11:51:48 +02:00
260d5b7aa7
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.
79 lines
2.4 KiB
C++
79 lines
2.4 KiB
C++
// Copyright 2009 Dolphin Emulator Project
|
|
// Licensed under GPLv2+
|
|
// Refer to the license.txt file included.
|
|
|
|
#include "VideoCommon/BPMemory.h"
|
|
|
|
#include <cstring>
|
|
|
|
// BP state
|
|
// STATE_TO_SAVE
|
|
BPMemory bpmem;
|
|
|
|
bool BlendMode::UseLogicOp() const
|
|
{
|
|
// Logicop bit has lowest priority.
|
|
if (subtract || blendenable || !logicopenable)
|
|
return false;
|
|
|
|
// Fast path for Kirby's Return to Dreamland, they use it with dstAlpha.
|
|
if (logicmode == BlendMode::NOOP)
|
|
return false;
|
|
|
|
return true;
|
|
}
|
|
|
|
bool FogParams::IsNaNCase() const
|
|
{
|
|
// Check for the case where both a and c are infinity or NaN.
|
|
// On hardware, this results in the following colors:
|
|
//
|
|
// -------------------------------------------------------
|
|
// | A | C | Result | A | C | Result |
|
|
// -------------------------------------------------------
|
|
// | inf | inf | Fogged | inf | nan | Fogged |
|
|
// | inf | -inf | Unfogged | inf | -nan | Unfogged |
|
|
// | -inf | inf | Unfogged | -inf | nan | Unfogged |
|
|
// | -inf | -inf | Unfogged | -inf | -nan | Unfogged |
|
|
// -------------------------------------------------------
|
|
// | nan | inf | Fogged | nan | nan | Fogged |
|
|
// | nan | -inf | Unfogged | nan | -nan | Unfogged |
|
|
// | -nan | inf | Unfogged | -nan | nan | Unfogged |
|
|
// | -nan | -inf | Unfogged | -nan | -nan | Unfogged |
|
|
// -------------------------------------------------------
|
|
//
|
|
// We replicate this by returning A=0, and C=inf for the inf/inf case, otherwise -inf.
|
|
// This ensures we do not pass a NaN to the GPU, and -inf/inf clamp to 0/1 respectively.
|
|
return a.exp == 255 && c_proj_fsel.c_exp == 255;
|
|
}
|
|
|
|
float FogParams::GetA() const
|
|
{
|
|
if (IsNaNCase())
|
|
return 0.0f;
|
|
|
|
// scale mantissa from 11 to 23 bits
|
|
const u32 integral = (static_cast<u32>(a.sign) << 31) | (static_cast<u32>(a.exp) << 23) |
|
|
(static_cast<u32>(a.mant) << 12);
|
|
|
|
float real;
|
|
std::memcpy(&real, &integral, sizeof(u32));
|
|
return real;
|
|
}
|
|
|
|
float FogParams::GetC() const
|
|
{
|
|
if (IsNaNCase())
|
|
{
|
|
constexpr float inf = std::numeric_limits<float>::infinity();
|
|
return !a.sign && !c_proj_fsel.c_sign ? -inf : inf;
|
|
}
|
|
|
|
// scale mantissa from 11 to 23 bits
|
|
const u32 integral = (c_proj_fsel.c_sign.Value() << 31) | (c_proj_fsel.c_exp.Value() << 23) |
|
|
(c_proj_fsel.c_mant.Value() << 12);
|
|
|
|
float real;
|
|
std::memcpy(&real, &integral, sizeof(u32));
|
|
return real;
|
|
}
|