[GLSL] rgb <=> hsv

GLSL_rgb2hsv_hsv2rgb.glsl

// RGB -> HSV
vec3 rgb2hsv(vec3 v){
	const float e=1e-20;
	vec4 c=vec4(v,0);
	c=mix(vec4(c.rbg,-1),c,step(c.b,c.g));
	c=mix(vec4(c.grb,-1.0/3.0-c.a),c,step(c.g,c.r));
	float cr=c.r-min(c.g,c.b);
	return vec3(abs(c.a+(c.g-c.b)/(6*cr+e)),cr/(c.r+e),c.r);
}
// HSV -> RGB
vec3 hsv2rgb(vec3 v){
	return (clamp(abs(fract(v.x+vec3(0,2,1)/3)*6-3)-2,-1,0)*v.y+1)*v.z;
}