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Why is software mode that precise?
#1
As title suggests... can anybody explain me why GSDX software mode is that precise?

Is the GS chip fully understood and completely emulated? I mean we don't have a precise FPU for the core.. Why are all calculations on the software emulated GS chip 100% accurate if even the core is far from achieving that?

Why is the texture cache of SW mode working nicely supporting mipmapping and solving current half-screen issues while the HW renderer is broken? Why do we have crc hacks only for HW renderer? The same for AlphaHack, WildArmsHack, TC offset,...

How could the SW renderer be so precice?

Are there known bugs in SW renderer?
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#2
Known software mode bugs: Shadow rendering on Jak and dexter , White lines on Boss battles of Ben10 protector of Earth.

from what I know, the software renderer only causes issues because of mistake in VU calculation other than that Software mode is pretty much accurate. though, I don't know exactly why it's far more accurate than hardware mode, only rendering of a Texture quad is done on software mode.

also most of the issues in hardware mode is triggered due to upscaling which causes different alpha values ranging and the computation of the texture coordinates will be entirely different and would eventually needed to be rounded to make sure that ends up in the Texture range and not some Invalid value (outside Texture), which have already been dealt with hacks like round sprite and align sprite.

Though I'm also quite curious on this super accuracy of the software mode. Smile
We're supposed to be working as a team, if we aren't helping and suggesting things to each other, we aren't working as a team.
- Refraction

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#3
There is also a bug in GTA because texture isn't reloaded as expected.

SW mode is accurate because it can
1/ emulate the GS memory format (which is really not compatible with current GPU).
2/ emulate the fixed function units of the GS (which have different behavior on the GPU)
3/ Use integer whereas GPU use float
4/ Don't use upscaling or extra filtering

On openGL except "upscaling hack" and CRC hack, all others hacks are mostly useless.
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#4
How is the performance (maybe FLOPS) of the GS chip in comparison to the EE (maybe + other core stuff)?

I think rounding and clamping on the GS should as well behave different then on a x86. I would expect that GS chip needs to be like 10x weaker than the EE to make full software emulation at higher accuracy in the same time... What about oversized registers or something like that? Stuff that is used on the GS that is not available in one cycle/atomic on an x86?

I have the feeling the four points you mention are the reason why HW mode is that bad - not why SW is that accurate.
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#5
GFLOPS doesn't mean anything. A float integer multiplication of the GS can be done on 1/8th of instruction. Whereas a not standard float on the VU would cost you 3-5 instructions (dunno the exact number).

The list is the difference between SW and HW. You can emulate anything with X86. GS can easily uses AVX whereas it is more difficult on the EE/VU. You can't compare both.
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#6
According to your statements, I guess a accurate hardware rendering is quite unlikely Sad , how is the GS memory format and those fixed functions of GS handled in hardware rendering ?
We're supposed to be working as a team, if we aren't helping and suggesting things to each other, we aren't working as a team.
- Refraction

[Image: 84t1dRu.png]
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#7
Sorry for being offtopic but I so very much want to tag refraction in this thread. Laugh
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#8
(07-15-2015, 06:46 PM)ssakash Wrote: According to your statements, I guess a accurate hardware rendering is quite unlikely Sad , how is the GS memory format and those fixed functions of GS handled in hardware rendering ?
Except upscaling which is a hack anyway. The only real issue is speed, otherwise lots of things can be fixed. You can do a kind of SW renderer in the shader directly Tongue2
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#9
There are faint lines in xenosaga III movies, but like other have mention is not 100% accurate but is much much more accurate then hw
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#10
Well it could also be rounding bug at VU level.
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