C#: Create a lighter/darker color based on a system color

Question

Duplicate

How do I adjust the brightness of a color?
How do I determine darker or lighter color variant of a given color?
Programmat

Answer 1

Here's some javascript code I use for lightening/darkening a given colour. You could use it as a base for an equivalent C# function

It works by calculating a distance from pure white of each of the RGB components and then adjusts this distance by the provided factor. The new distance is used to calculate the new colour. A factor of between 0 and 1 darkens, a factor higher than 1 lightens

function Darken( hexColor, factor )
    {   
        if ( factor < 0 ) factor = 0;

        var c = hexColor;
        if ( c.substr(0,1) == "#" )
        {
            c = c.substring(1);
        }

        if ( c.length == 3 || c.length == 6 )
        {
            var i = c.length / 3;

            var f;  // the relative distance from white

            var r = parseInt( c.substr(0, i ), 16 );
            f = ( factor * r / (256-r) );
            r = Math.floor((256 * f) / (f+1));

            r = r.toString(16);
            if ( r.length == 1 ) r = "0" + r;

            var g = parseInt( c.substr(i, i), 16);
            f = ( factor * g / (256-g) );
            g = Math.floor((256 * f) / (f+1));
            g = g.toString(16);
            if ( g.length == 1 ) g = "0" + g;

            var b = parseInt( c.substr( 2*i, i),16 );
            f = ( factor * b / (256-b) );
            b = Math.floor((256 * f) / (f+1));
            b = b.toString(16);
            if ( b.length == 1 ) b = "0" + b;

            c =  r+g+b;
         }   

         return "#" + c;

    }