hsb to rgb

from http://nuttybar.drama.uga.edu/pipermail/dirgames-l/2001-March/006061.html

hsb to rgb

//Input:   hue, saturation, and brightness as floats scaled from 0.0 to 1.0
//Output:  red, green, and blue as floats scaled from 0.0 to 1.0

    if (brightness == 0.0)
    {   // safety short circuit again
        red   = 0.0;
        green = 0.0;
        blue  = 0.0;
        return;
    }

    if (saturation == 0.0)
    {   // grey
        red   = brightness;
        green = brightness;
        blue  = brightness;
        return;
    }

    float domainOffset;         // hue mod 1/6
    if (hue < 1.0/6)
    {   // red domain; green ascends
        domainOffset = hue;
        red   = brightness;
        blue  = brightness * (1.0 - saturation);
        green = blue + (brightness - blue) * domainOffset * 6;
    }
      else if (hue < 2.0/6)
      { // yellow domain; red descends
        domainOffset = hue - 1.0/6;
        green = brightness;
        blue  = brightness * (1.0 - saturation);
        red   = green - (brightness - blue) * domainOffset * 6;
      }
      else if (hue < 3.0/6)
      { // green domain; blue ascends
        domainOffset = hue - 2.0/6;
        green = brightness;
        red   = brightness * (1.0 - saturation);
        blue  = red + (brightness - red) * domainOffset * 6;
      }
      else if (hue < 4.0/6)
      { // cyan domain; green descends
        domainOffset = hue - 3.0/6;
        blue  = brightness;
        red   = brightness * (1.0 - saturation);
        green = blue - (brightness - red) * domainOffset * 6;
      }
      else if (hue < 5.0/6)
      { // blue domain; red ascends
        domainOffset = hue - 4.0/6;
        blue  = brightness;
        green = brightness * (1.0 - saturation);
        red   = green + (brightness - green) * domainOffset * 6;
      }
      else
      { // magenta domain; blue descends
        domainOffset = hue - 5.0/6;
        red   = brightness;
        green = brightness * (1.0 - saturation);
        blue  = red - (brightness - green) * domainOffset * 6;
      }

    return;

rgb to hsb

//Input:   red, green, and blue as integers scaled from 0 to 255
//Output:  hue, saturation, and brightness as floats scaled from 0.0 to 1.0

    int bri = max(red, green, blue);
    if (bri == 0)
    {   // short-circuit now and avoid division by zero problems later
        brightness = 0.0;
        saturation = 0.0;
        hue        = 0.0;
        return;
    }

    brightness = bri / 255.0;
    int desaturator = min(red, green, blue);
    if (bri == desaturator)
    {   // we're grey (and still have division by zero issues to bypass)
        saturation = 0.0;
        hue        = 0.0;
        return;
    }

    saturation = (brightness - (desaturator / 255.0)) / brightness;
    int midigator = mid(red, green, blue);

    // "domains" are 60 degrees of red, yellow, green, cyan, blue, or magenta
    // compute how far we are from a domain base
    float domainBase;
    float oneSixth = 1.0f / 6.0f;
    float domainOffset = (midigator - desaturator) /
                         (float)(bri - desaturator) / 6.0;
    if (red == bri)
    {
        if (midigator == green)
	{   // green is ascending
            domainBase = 0 / 6.0;       // red domain
	}
          else
	  { // blue is descending
            domainBase = 5 / 6.0;       // magenta domain
	    domainOffset = oneSixth - domainOffset;
	  }
    }
      else if (grn == bri)
      {
        if (midigator == blue)
	{   // blue is ascending
            domainBase = 2 / 6.0;       // green domain
	}
          else
	  { // red is descending
            domainBase = 1 / 6.0;       // yellow domain
	    domainOffset = oneSixth - domainOffset;
	  }
      }
      else
      {
        if (midigator == red)
	{   // red is ascending
            domainBase = 4 / 6.0;       // blue domain
	}
          else
	  { // green is descending
            domainBase = 3 / 6.0;       // cyan domain
	    domainOffset = oneSixth - domainOffset;
	  }
      }

    hue = domainBase + domainOffset;
    return;