JS function to calculate complementary colour?

Question

Does anybody know, off the top of your heads, a Javascript solution for calculating the complementary colour of a hex value?

There is a number of colour picking suites and palette generators on the web but I haven't seen any that calculate the colour live using JS.

A detailed hint or a snippet would be very much appreciated.

Answer 1

Parsed through http://design.geckotribe.com/colorwheel/

    // Complement
    temprgb={ r: 0, g: 0xff, b: 0xff }; // Cyan
    temphsv=RGB2HSV(temprgb);
    temphsv.hue=HueShift(temphsv.hue,180.0);
    temprgb=HSV2RGB(temphsv);
    console.log(temprgb); // Complement is red (0xff, 0, 0)
    
    function RGB2HSV(rgb) {
    	hsv = new Object();
    	max=max3(rgb.r,rgb.g,rgb.b);
    	dif=max-min3(rgb.r,rgb.g,rgb.b);
    	hsv.saturation=(max==0.0)?0:(100*dif/max);
    	if (hsv.saturation==0) hsv.hue=0;
     	else if (rgb.r==max) hsv.hue=60.0*(rgb.g-rgb.b)/dif;
    	else if (rgb.g==max) hsv.hue=120.0+60.0*(rgb.b-rgb.r)/dif;
    	else if (rgb.b==max) hsv.hue=240.0+60.0*(rgb.r-rgb.g)/dif;
    	if (hsv.hue<0.0) hsv.hue+=360.0;
    	hsv.value=Math.round(max*100/255);
    	hsv.hue=Math.round(hsv.hue);
    	hsv.saturation=Math.round(hsv.saturation);
    	return hsv;
    }
    
    // RGB2HSV and HSV2RGB are based on Color Match Remix [http://color.twysted.net/]
    // which is based on or copied from ColorMatch 5K [http://colormatch.dk/]
    function HSV2RGB(hsv) {
    	var rgb=new Object();
    	if (hsv.saturation==0) {
    		rgb.r=rgb.g=rgb.b=Math.round(hsv.value*2.55);
    	} else {
    		hsv.hue/=60;
    		hsv.saturation/=100;
    		hsv.value/=100;
    		i=Math.floor(hsv.hue);
    		f=hsv.hue-i;
    		p=hsv.value*(1-hsv.saturation);
    		q=hsv.value*(1-hsv.saturation*f);
    		t=hsv.value*(1-hsv.saturation*(1-f));
    		switch(i) {
    		case 0: rgb.r=hsv.value; rgb.g=t; rgb.b=p; break;
    		case 1: rgb.r=q; rgb.g=hsv.value; rgb.b=p; break;
    		case 2: rgb.r=p; rgb.g=hsv.value; rgb.b=t; break;
    		case 3: rgb.r=p; rgb.g=q; rgb.b=hsv.value; break;
    		case 4: rgb.r=t; rgb.g=p; rgb.b=hsv.value; break;
    		default: rgb.r=hsv.value; rgb.g=p; rgb.b=q;
    		}
    		rgb.r=Math.round(rgb.r*255);
    		rgb.g=Math.round(rgb.g*255);
    		rgb.b=Math.round(rgb.b*255);
    	}
    	return rgb;
    }

    //Adding HueShift via Jacob (see comments)
    function HueShift(h,s) { 
        h+=s; while (h>=360.0) h-=360.0; while (h<0.0) h+=360.0; return h; 
    }
    
    //min max via Hairgami_Master (see comments)
    function min3(a,b,c) { 
        return (a<b)?((a<c)?a:c):((b<c)?b:c); 
    } 
    function max3(a,b,c) { 
        return (a>b)?((a>c)?a:c):((b>c)?b:c); 
    }