Petr Kobalíček has spurred me on to look more closely at the the HLSL conversion between RGB and HSV colour spaces. With a bit of refactoring, I've managed to shave a few more GPU cycles off:
float3 RGBtoHSV(in float3 RGB)
{
float3 HSV = 0;
#if NO_ASM
HSV.z = max(RGB.r, max(RGB.g, RGB.b));
float M = min(RGB.r, min(RGB.g, RGB.b));
float C = HSV.z - M;
#else
float4 RGB4 = RGB.rgbr;
asm { max4 HSV.z, RGB4 };
asm { max4 RGB4.w, -RGB4 };
float C = HSV.z + RGB4.w;
#endif
if (C != 0)
{
float RGB0 = float4(RGB, 0);
float4 Delta = (HSV.z - RGB0) / C;
Delta.rgb -= Delta.brg;
Delta.rgb += float3(2,4,6);
Delta.rgb *= step(HSV.z, RGB.gbr);
#if NO_ASM
HSV.x = max(Delta.r, max(Delta.g, Delta.b));
#else
float4 Delta4 = Delta.rgbr;
asm { max4 HSV.x, Delta4 };
#endif
HSV.x = frac(HSV.x / 6);
HSV.y = 1 / Delta.w;
}
return HSV;
}
Monday 31 January 2011
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