编/解码浮点值到RGBA

inline float4 EncodeFloatRGBA( float v ) {
float4 enc = float4(1.0, 255.0, 65025.0, 160581375.0) * v;
enc = frac(enc);
enc -= enc.yzww * float4(1.0/255.0,1.0/255.0,1.0/255.0,0.0);
return enc;
}

inline float DecodeFloatRGBA( float4 rgba ) {
return dot( rgba, float4(1.0, 1/255.0, 1/65025.0, 1/160581375.0) );
}