Class: Color::Palette::MonoContrast
- Inherits:
-
Object
- Object
- Color::Palette::MonoContrast
- Defined in:
- lib/color/palette/monocontrast.rb
Overview
Generates a monochromatic constrasting colour palette for background and foreground. What does this mean?
Monochromatic: A single colour is used to generate the base palette, and this colour is lightened five times and darkened five times to provide eleven distinct colours.
Contrasting: The foreground is also generated as a monochromatic colour palette; however, all generated colours are tested to see that they are appropriately contrasting to ensure maximum readability of the foreground against the background.
Constant Summary collapse
- DEFAULT_MINIMUM_BRIGHTNESS_DIFF =
(125.0 / 255.0)
- DEFAULT_MINIMUM_COLOR_DIFF =
(500.0 / 255.0)
Instance Attribute Summary collapse
-
#background ⇒ Object
readonly
Hash of CSS background colour values.
-
#foreground ⇒ Object
readonly
Hash of CSS foreground colour values.
-
#minimum_brightness_diff ⇒ Object
The minimum brightness difference between the background and the foreground, and must be between 0..1.
-
#minimum_color_diff ⇒ Object
The minimum colour difference between the background and the foreground, and must be between 0..3.
Instance Method Summary collapse
-
#brightness_diff(c1, c2) ⇒ Object
Returns the absolute difference between the brightness levels of two colours.
-
#calculate_foreground(background, foreground) ⇒ Object
Given a background colour and a foreground colour, modifies the foreground colour so that it will have enough contrast to be seen against the background colour.
-
#color_diff(c1, c2) ⇒ Object
Returns the contrast between to colours, a decimal value between 0 and 3.
-
#initialize(background, foreground = nil) ⇒ MonoContrast
constructor
Generate the initial palette.
-
#regenerate(background, foreground = nil) ⇒ Object
Generate the colour palettes.
Constructor Details
#initialize(background, foreground = nil) ⇒ MonoContrast
Generate the initial palette.
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# File 'lib/color/palette/monocontrast.rb', line 88 def initialize(background, foreground = nil) @minimum_brightness_diff = DEFAULT_MINIMUM_BRIGHTNESS_DIFF @minimum_color_diff = DEFAULT_MINIMUM_COLOR_DIFF regenerate(background, foreground) end |
Instance Attribute Details
#background ⇒ Object (readonly)
Hash of CSS background colour values.
This is always 11 values:
- 0
-
The starting colour.
- 1..5
-
Lighter colours.
- -1..-5
-
Darker colours.
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# File 'lib/color/palette/monocontrast.rb', line 34 def background @background end |
#foreground ⇒ Object (readonly)
Hash of CSS foreground colour values.
This is always 11 values:
- 0
-
The starting colour.
- 1..5
-
Lighter colours.
- -1..-5
-
Darker colours.
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# File 'lib/color/palette/monocontrast.rb', line 42 def foreground @foreground end |
#minimum_brightness_diff ⇒ Object
The minimum brightness difference between the background and the foreground, and must be between 0..1. Setting this value will regenerate the palette based on the base colours. The default value for this is 125 / 255.0. If this value is set to nil
, it will be restored to the default.
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# File 'lib/color/palette/monocontrast.rb', line 51 def minimum_brightness_diff @minimum_brightness_diff end |
#minimum_color_diff ⇒ Object
The minimum colour difference between the background and the foreground, and must be between 0..3. Setting this value will regenerate the palette based on the base colours. The default value for this is 500 / 255.0.
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# File 'lib/color/palette/monocontrast.rb', line 72 def minimum_color_diff @minimum_color_diff end |
Instance Method Details
#brightness_diff(c1, c2) ⇒ Object
Returns the absolute difference between the brightness levels of two colours. This will be a decimal value between 0 and 1. W3C accessibility guidelines for colour contrast suggest that this value be at least approximately 0.49 (125 / 255.0) for proper contrast.
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# File 'lib/color/palette/monocontrast.rb', line 166 def brightness_diff(c1, c2) (c1.brightness - c2.brightness).abs end |
#calculate_foreground(background, foreground) ⇒ Object
Given a background colour and a foreground colour, modifies the foreground colour so that it will have enough contrast to be seen against the background colour.
Uses #mininum_brightness_diff and #minimum_color_diff.
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# File 'lib/color/palette/monocontrast.rb', line 134 def calculate_foreground(background, foreground) nfg = nil # Loop through brighter and darker versions of the foreground color. The # numbers here represent the amount of foreground color to mix with # black and white. [100, 75, 50, 25, 0].each do |percent| dfg = foreground.darken_by(percent) lfg = foreground.lighten_by(percent) dbd = brightness_diff(background, dfg) lbd = brightness_diff(background, lfg) if lbd > dbd nfg = lfg nbd = lbd else nfg = dfg nbd = dbd end ncd = color_diff(background, nfg) break if nbd >= @minimum_brightness_diff and ncd >= @minimum_color_diff end nfg end |
#color_diff(c1, c2) ⇒ Object
Returns the contrast between to colours, a decimal value between 0 and
-
W3C accessibility guidelines for colour
contrast suggest that this value be at least approximately 1.96 (500 / 255.0) for proper contrast.
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# File 'lib/color/palette/monocontrast.rb', line 174 def color_diff(c1, c2) r = (c1.r - c2.r).abs g = (c1.g - c2.g).abs b = (c1.b - c2.b).abs r + g + b end |
#regenerate(background, foreground = nil) ⇒ Object
Generate the colour palettes.
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# File 'lib/color/palette/monocontrast.rb', line 96 def regenerate(background, foreground = nil) foreground ||= background background = background.to_rgb foreground = foreground.to_rgb @background = {} @foreground = {} @background[-5] = background.darken_by(10) @background[-4] = background.darken_by(25) @background[-3] = background.darken_by(50) @background[-2] = background.darken_by(75) @background[-1] = background.darken_by(85) @background[ 0] = background @background[+1] = background.lighten_by(85) @background[+2] = background.lighten_by(75) @background[+3] = background.lighten_by(50) @background[+4] = background.lighten_by(25) @background[+5] = background.lighten_by(10) @foreground[-5] = calculate_foreground(@background[-5], foreground) @foreground[-4] = calculate_foreground(@background[-4], foreground) @foreground[-3] = calculate_foreground(@background[-3], foreground) @foreground[-2] = calculate_foreground(@background[-2], foreground) @foreground[-1] = calculate_foreground(@background[-1], foreground) @foreground[ 0] = calculate_foreground(@background[ 0], foreground) @foreground[+1] = calculate_foreground(@background[+1], foreground) @foreground[+2] = calculate_foreground(@background[+2], foreground) @foreground[+3] = calculate_foreground(@background[+3], foreground) @foreground[+4] = calculate_foreground(@background[+4], foreground) @foreground[+5] = calculate_foreground(@background[+5], foreground) end |