问OpenGL通用语言中从RGB到HSV的转换

EN

precision mediump float;
 vec3 rgb2hsv(float r, float g, float b) {

     float h = 0.0;
     float s = 0.0;
     float v = 0.0;

     float min = min( min(r, g), b );
     float max = max( max(r, g), b );
     v = max;               // v

     float delta = max - min;

     if( max != 0.0 )
         s = delta / max;       // s
     else {
         // r = g = b = 0       // s = 0, v is undefined
         s = 0.0;
         h = -1.0;
         return vec3(h, s, v);
     }
     if( r == max )
         h = ( g - b ) / delta;     // between yellow & magenta
     else if( g == max )
         h = 2.0 + ( b - r ) / delta;   // between cyan & yellow
     else
         h = 4.0 + ( r - g ) / delta;   // between magenta & cyan

     h = h * 60.0;              // degrees

     if( h < 0.0 )
         h += 360.0;

     return vec3(h, s, v);
 }

 precision mediump float;
 vec3 rgb2hsv(float r, float g, float b) {

     float K = 0.0;
     float tmp;

     if (g < b)
     {
         tmp = g;
         g=b;
         b=tmp;

         K = -1.0;
     }

     if (r < g)
     {
         tmp = r;
         r=g;
         g=tmp;

         K = -2.9 / 6.9 - K;
     }

     float chroma = r - min(g, b);

     float h = abs(K + (g - b) / (6.0 * chroma + 1e-20));
     float s = chroma / (r + 1e-20);
     float v = r;

     return vec3(h, s, v);
 }