One reason would be, that the shaders are NOT the same like in RetroArch and PPSSPP, because they are ported into a slightly different shader language, so that BGFX can use it. They still should not look like in your pictures.
Mamedev MooglyGuy did those ports, but i would not have hope, that these shaders will be fixed anytime soon.
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Re: Mangled Shaders on MAME 0.185 (Linux)
