Add .darken and .lighten methods to UIColor.

[silasjmatson]

Changes the brightness using the HSB values.

[colinta]

I love the idea! I think we'll ned to tweak the implementation a bit. For instance, this doesn't use the existing brightness value, so calling darken(10).darken(10) is the same as just .darken(10). Also, any positive value for lighten will result in "white", no matter what color you start with. This is because new_brightness = (100 + percent) / 100 will be > 1 if percent is positive.

(main)> '#ffffff'.uicolor.darken(10.0)
=> '#e5e5e5'.uicolor
(main)> '#ffffff'.uicolor.darken(10.0).darken(10.0)  # calling darken a second time
=> '#e5e5e5'.uicolor
(nil)? '#e5e5e5'.uicolor.lighten(10.0)
=> :white.uicolor
(main)> '#e5e5e5'.uicolor.lighten(1)
=> :white.uicolor
(main)> '#000000'.uicolor.lighten(1)
=> :white.uicolor

[colinta]

I'm thinking that we should encourage the "raw values" that the brightness: argument accepts, too. What do you think about this:

  def darken(amount=0.1)
    change_brightness -amount
  end

  def lighten(amount=0.1)
    change_brightness amount
  end

  def change_brightness(amount)
    new_brightness = brightness + amount
    UIColor.colorWithHue(hue, saturation: saturation, brightness: new_brightness, alpha: alpha)
  end

[silasjmatson]

I apparently didn't test as well as I thought. :tongue: My original implementation used the original brightness, but somehow it changed to not include it. Probably one of my "let's simplify things" refactors.

I think using raw values works just as well. We are programmers, after all. And it makes the implementation easy!

[silasjmatson]

Is this behavior expected?

(main)> "#ffffff".uicolor.darken(0.1).lighten(0.1)
=> :white.uicolor
(main)> "#ffffff".uicolor.darken(0.1).lighten(0.1).hex
=> "#ffffff"
(nil)? '#e5e5e5'.uicolor.lighten(0.1).hex
=> "#fefefe"

It makes sense when I think about it (limitations of RGB color space), but colors make my head hurt. Maybe we want to find an actual algorithm and allow adjusting using either RGB or HSB?

[colinta]

Meh, I think just pushing the brightness up and down works well. Thoughts on this? ad13a6a

[silasjmatson]

:+1: :shipit: Looks good to me!

[colinta]

Done! Available in 3.0.5. Thanks!