A number of games make an EFB copy in I4/I8 format, then use it as a
texture in C4/C8 format. Detect when this happens, and decode the copy on
the GPU using the specified palette.
This has a few advantages: it allows using EFB2Tex for a few more games,
it, it preserves the resolution of scaled EFB copies, and it's probably a
bit faster.
D3D only at the moment, but porting to OpenGL should be straightforward..
The obvious question here is, why does it matter if we round or truncate?
The key is that GC/Wii does fixed-point interpolation, where PC GPUs do
floating-point interpolation. Discarding fractional bits makes the conversion
from floating-point to fixed point give more consistent results.
I'm not confident this is really the right fix, or that my explanation is
completely correct; ideally, we don't want to depend on floating-point
interpolation at all.
For more information:
https://docs.google.com/document/d/1tBEgsJh7QiwNwepXI0eobfK3U8LkJButSyeuFt1degM/edit?usp=sharing
removed: SSE includes (not used)
added: 16bit -> float -> 16bit functions
added: linear interpolator and high-quality (windowed-sinc) interpolator functions (including Resampler class)
added: dithering
changed: renamed variables and reformatted a few things to fit with style guide (braces, #include->const)
changed: use s16, u16, s32, u32 etc
changed: store samples and do all computations as floats
changed: volume from 0 - 255
This is the same trick which is used for Metroid's fonts/texts, but for all textures. If 2 different textures at the same address are loaded during the same frame, create a 2nd entry instead of overwriting the existing one. If the entry was overwritten in this case, there wouldn't be any caching, which results in a big performance drop.
The restriction to textures, which are loaded during the same frame, prevents creating lots of textures when textures are used in the regular way. This restriction is new. Overwriting textures, instead of creating new ones is faster, if the old ones are unlikely to be used again.
Since this would break efb copies, don't do it for efb copies.
Castlevania 3 goes from 80 fps to 115 fps for me.
There might be games that need a higher texture cache accuracy with this, but those games should also see a performance boost from this PR.
Some games, which use paletted textures, which are not efb copies, might be faster now. And also not require a higher texture cache accuracy anymore. (similar sitation as PR https://github.com/dolphin-emu/dolphin/pull/1916)
Pierre Bourdon