Some games (e.g. Metal Gear Solid 2) use large-ish textures, with a
bunch of different CLUTs/palettes, depending on the draw. Kind-of like a
texture atlas.
This causes issues when texture preloading is enabled, as both VRAM and
GS CPU thread usage increase proporiately to the number of texture:clut
pairs (since it has to be hashed).
An alternative to disabling preloading, which is what we currently do,
is enabling GPU palette conversion in these games. Even though we
ever-so-slightly increase the GPU load due to having to do shader
sampling, the CPU load on the GS thread is considerably reduced, and
overall performance is greater. In theory it'll also achieve higher
cache hit rates on the GPU, since we're not duplicating a bunch of
textures.
However, as a general rule of thumb, we don't want to encourage people
to enable paltex, as most games run slower with it on. So, what this PR
does, is add a GameDB option for these types of games, to enable paltex
when texture preloading is set to full/hash cache, but otherwise leave
the setting alone. The best of both worlds.
NOTE: I've also forced paltex=0 for Spider-Man 2, as it uses a massive
number of palettes which can cause descriptor issues in DX12/Vulkan. A
perfect example of where you *don't* want to use paltex.
Connor McLaughlin