JS function to calculate complementary color?

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

The tool:
http://colorschemedesigner.com/

The code:
http://colorschemedesigner.com/js/color.js

The code itself is pretty beastly, so good luck parsing.

Answer 2

Here is a site that does a lot more, but it uses javascript.

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

http://design.geckotribe.com/colorwheel/colorwheel.js

Answer 3

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

// complement
temprgb=thisrgb;
temphsv=RGB2HSV(temprgb);
temphsv.hue=HueShift(temphsv.hue,180.0);
temprgb=HSV2RGB(temphsv);

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;
}