One Quickie

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Converting RGB to HSL (Graphics->General)

Some color manipulations are easier in HSL than RGB.

// Based on Foley and van Dam algorithm.
void ConvertRGBToHSL (const CGFloat *rgbComponents, CGFloat *hslComponents) {
    CGFloat red = rgbComponents[0];
    CGFloat green = rgbComponents[1];
    CGFloat blue = rgbComponents[2];

    CGFloat maxColor = MAX (red, MAX (green, blue));
    CGFloat minColor = MIN (red, MIN (green, blue));
    CGFloat deltaColor = maxColor - minColor;

    CGFloat hue, saturation;
    CGFloat lightness =  (maxColor + minColor) / 2.0;

    // All the same means a gray color.
    if (maxColor == minColor) {
        saturation = 0.0;
        hue = 0.0;  // officially undefined with gray, but go ahead and zero out.

    } else {
        if (lightness < 0.5) saturation = deltaColor / (maxColor + minColor);
        else                 saturation = deltaColor / (2.0 - deltaColor);

        if (red == maxColor)        hue = (green - blue) / deltaColor;
        else if (green == maxColor) hue = 2.0 + (blue - red) / deltaColor;
        else                        hue = 4.0 + (red - green) / deltaColor;

        // H will be in the range of 0..6, convert to degrees.
        hue *= 60.0;

        // Convert to positive angle.
        if (hue < 0) hue += 360.0;
    }

    // Clamp to legal values.
    hslComponents[0] = MAX (0.0, MIN (360.0, hue));
    hslComponents[1] = MAX (0.0, MIN (1.0, saturation));
    hslComponents[2] = MAX (0.0, MIN (1.0, lightness));

} // ConvertRGBToHSL