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GPU: Truncate instead of rounding 24bpp->16bpp 

Thanks to axetion for writing a test to confirm this is what the console
GPU indeed does.
This commit is contained in:
Connor McLaughlin 2022-12-20 21:19:05 +10:00
parent 1c8ef86f12
commit d65cbe42ae
2 changed files with 20 additions and 19 deletions
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13
src/core/gpu_sw.cpp
View File

@ -142,16 +142,21 @@ ALWAYS_INLINE u16 VRAM16ToOutput<GPUTexture::Format::RGB565, u16>(u16 value)
template<> template<>
ALWAYS_INLINE u32 VRAM16ToOutput<GPUTexture::Format::RGBA8, u32>(u16 value) ALWAYS_INLINE u32 VRAM16ToOutput<GPUTexture::Format::RGBA8, u32>(u16 value)
{ {
return VRAMRGBA5551ToRGBA8888(value); const u32 value32 = ZeroExtend32(value);
const u32 r = (value32 & 31u) << 3;
const u32 g = ((value32 >> 5) & 31u) << 3;
const u32 b = ((value32 >> 10) & 31u) << 3;
const u32 a = ((value >> 15) != 0) ? 255 : 0;
return ZeroExtend32(r) | (ZeroExtend32(g) << 8) | (ZeroExtend32(b) << 16) | (ZeroExtend32(a) << 24);
} }
template<> template<>
ALWAYS_INLINE u32 VRAM16ToOutput<GPUTexture::Format::BGRA8, u32>(u16 value) ALWAYS_INLINE u32 VRAM16ToOutput<GPUTexture::Format::BGRA8, u32>(u16 value)
{ {
const u32 value32 = ZeroExtend32(value); const u32 value32 = ZeroExtend32(value);
const u32 r = VRAMConvert5To8(value32 & 31u); const u32 r = (value32 & 31u) << 3;
const u32 g = VRAMConvert5To8((value32 >> 5) & 31u); const u32 g = ((value32 >> 5) & 31u) << 3;
const u32 b = VRAMConvert5To8((value32 >> 10) & 31u); const u32 b = ((value32 >> 10) & 31u) << 3;
return ZeroExtend32(b) | (ZeroExtend32(g) << 8) | (ZeroExtend32(r) << 16) | (0xFF000000u); return ZeroExtend32(b) | (ZeroExtend32(g) << 8) | (ZeroExtend32(r) << 16) | (0xFF000000u);
} }

26
src/core/gpu_types.h
View File

@ -117,29 +117,25 @@ union GPURenderCommand
} }
}; };
// Helper/format conversion functions - constants from https://stackoverflow.com/a/9069480
ALWAYS_INLINE static constexpr u32 VRAMConvert5To8(u32 color)
{
return (((color * 527u) + 23u) >> 6);
}
ALWAYS_INLINE static constexpr u32 VRAMConvert8To5(u32 color)
{
return (((color * 249u) + 1014u) >> 11);
}
ALWAYS_INLINE static constexpr u32 VRAMRGBA5551ToRGBA8888(u32 color) ALWAYS_INLINE static constexpr u32 VRAMRGBA5551ToRGBA8888(u32 color)
{ {
const u32 r = VRAMConvert5To8(color & 31u); // Helper/format conversion functions - constants from https://stackoverflow.com/a/9069480
const u32 g = VRAMConvert5To8((color >> 5) & 31u); #define E5TO8(color) ((((color) * 527u) + 23u) >> 6)
const u32 b = VRAMConvert5To8((color >> 10) & 31u);
const u32 r = E5TO8(color & 31u);
const u32 g = E5TO8((color >> 5) & 31u);
const u32 b = E5TO8((color >> 10) & 31u);
const u32 a = ((color >> 15) != 0) ? 255 : 0; const u32 a = ((color >> 15) != 0) ? 255 : 0;
return ZeroExtend32(r) | (ZeroExtend32(g) << 8) | (ZeroExtend32(b) << 16) | (ZeroExtend32(a) << 24); return ZeroExtend32(r) | (ZeroExtend32(g) << 8) | (ZeroExtend32(b) << 16) | (ZeroExtend32(a) << 24);
#undef E5TO8
} }
ALWAYS_INLINE static constexpr u16 VRAMRGBA8888ToRGBA5551(u32 color) ALWAYS_INLINE static constexpr u16 VRAMRGBA8888ToRGBA5551(u32 color)
{ {
const u32 r = VRAMConvert8To5(color & 0xFFu); const u32 r = (color & 0xFFu) >> 3;
const u32 g = VRAMConvert8To5((color >> 8) & 0xFFu); const u32 g = ((color >> 8) & 0xFFu) >> 3;
const u32 b = VRAMConvert8To5((color >> 16) & 0xFFu); const u32 b = ((color >> 16) & 0xFFu) >> 3;
const u32 a = ((color >> 24) & 0x01u); const u32 a = ((color >> 24) & 0x01u);
return Truncate16(r | (g << 5) | (b << 10) | (a << 15)); return Truncate16(r | (g << 5) | (b << 10) | (a << 15));
} }