Module:Color contrast/sandbox: Difference between revisions

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This module is used primarily by

• {{Color contrast ratio}}
• {{RGBColorToLum}}
• {{Color contrast conformance}}
• {{Ensure AAA contrast ratio}}
• {{Ensure AA contrast ratio}}
• {{Greater color contrast ratio}}

It is also used for tracking within

• Module:Navbox
• Module:Userbox
• Module:Episode list

and for documentation in

• Module:College color

The formulas used are stated in WCAG 2.x specifications. WCAG is the main guideline for creating accessible interfaces on the web.

Usage

To use this module, you may use one of the above listed templates or invoke the module directly

• To compute relative luminescence:
  {{RGBColorToLum|color}} or {{#invoke:Color contrast|lum|color}}
• To compute a contrast ratio between two colors:
  {{Color contrast ratio|color1|color2|error=?}} or {{#invoke:Color contrast|ratio|color1|color2|error=?}}
• To determine which of two colors (color2a and color2b) has the greater contrast ratio with a particular color (color1):
  {{Greater color contrast ratio|color1|color2a|color2b}} or {{#invoke:Color contrast|greatercontrast|color1|color2a|color2b}}
• To compute the contrast ratio between the background and text colors specified in a css style string:
  {{#invoke:Color contrast|styleratio|css style statement string|default background color|default text color}}

The above documentation is transcluded from Module:Color contrast/doc. (edit | history)
Editors can experiment in this module's sandbox (edit | diff) and testcases (create) pages.
Add categories to the /doc subpage. Subpages of this module.

--
-- This module implements 
--  {{Color contrast ratio}}
--  {{Greater color contrast ratio}}
--  {{ColorToLum}}
--  {{RGBColorToLum}}
--
local p = {}
local HTMLcolor = mw.loadData( 'Module:Color contrast/colors' )

local function sRGB ( v ) 
	if (v <= 0.03928) then 
		v = v / 12.92
	else
		v = math.pow((v+0.055)/1.055, 2.4)
	end
	return v
end

local function rgbdec2lum( R, G, B )
	if ( 0 <= R and R < 256 and 0 <= G and G < 256 and 0 <= B and B < 256 ) then
		return 0.2126 * sRGB(R/255) + 0.7152 * sRGB(G/255) + 0.0722 * sRGB(B/255)
	else
		return ''
	end
end

local function hsl2lum( h, s, l )
	if ( 0 <= h and h < 360 and 0 <= s and s <= 1 and 0 <= l and l <= 1 ) then
		local c = (1 - math.abs(2*l - 1))*s
		local x = c*(1 - math.abs( math.fmod(h/60, 2) - 1) )
		local m = l - c/2

		local r, g, b = m, m, m
		if( 0 <= h and h < 60 ) then
			r = r + c
			g = g + x
		elseif( 60 <= h and h < 120 ) then
			r = r + x
			g = g + c
		elseif( 120 <= h and h < 180 ) then
			g = g + c
			b = b + x
		elseif( 180 <= h and h < 240 ) then
			g = g + x
			b = b + c
		elseif( 240 <= h and h < 300 ) then
			r = r + x
			b = b + c
		elseif( 300 <= h and h < 360 ) then
			r = r + c
			b = b + x
		end
		return rgbdec2lum(255*r, 255*g, 255*b)
	else
		return ''
	end
end

local function color2lum( c )

	if (c == nil) then
		return ''
	end
	-- whitespace
	c = c:match( '^%s*(.-)[%s;]*$' )

	-- lowercase
	c = c:lower()

	-- first try to look it up
	local L = HTMLcolor[c]
	if (L ~= nil) then
		return L
	end

   	-- convert from hsl
   	if mw.ustring.match(c,'^hsl%([%s]*[0-9][0-9%.]*[%s]*,[%s]*[0-9][0-9%.]*%%[%s]*,[%s]*[0-9][0-9%.]*%%[%s]*%)$') then
		local h, s, l = mw.ustring.match(c,'^hsl%([%s]*([0-9][0-9%.]*)[%s]*,[%s]*([0-9][0-9%.]*)%%[%s]*,[%s]*([0-9][0-9%.]*)%%[%s]*%)$')
		return hsl2lum(tonumber(h), tonumber(s)/100, tonumber(l)/100)
   	end

   	-- convert from rgb
   	if mw.ustring.match(c,'^rgb%([%s]*[0-9][0-9]*[%s]*,[%s]*[0-9][0-9]*[%s]*,[%s]*[0-9][0-9]*[%s]*%)$') then
		local R, G, B = mw.ustring.match(c,'^rgb%([%s]*([0-9][0-9]*)[%s]*,[%s]*([0-9][0-9]*)[%s]*,[%s]*([0-9][0-9]*)[%s]*%)$')
		return rgbdec2lum(tonumber(R), tonumber(G), tonumber(B))
   	end

   	-- convert from rgb percent
   	if mw.ustring.match(c,'^rgb%([%s]*[0-9][0-9%.]*%%[%s]*,[%s]*[0-9][0-9%.]*%%[%s]*,[%s]*[0-9][0-9%.]*%%[%s]*%)$') then
		local R, G, B = mw.ustring.match(c,'^rgb%([%s]*([0-9][0-9%.]*)%%[%s]*,[%s]*([0-9][0-9%.]*)%%[%s]*,[%s]*([0-9][0-9%.]*)%%[%s]*%)$')
		return rgbdec2lum(255*tonumber(R)/100, 255*tonumber(G)/100, 255*tonumber(B)/100)
   	end

	-- remove leading # (if there is one) and whitespace
	c = mw.ustring.match(c, '^[%s#]*([a-f0-9]*)[%s]*$')

	-- split into rgb
	local cs = mw.text.split(c or '', '')
	if( #cs == 6 ) then
		local R = 16*tonumber('0x' .. cs[1]) + tonumber('0x' .. cs[2])
		local G = 16*tonumber('0x' .. cs[3]) + tonumber('0x' .. cs[4])
		local B = 16*tonumber('0x' .. cs[5]) + tonumber('0x' .. cs[6])

		return rgbdec2lum(R, G, B)
	elseif ( #cs == 3 ) then
		local R = 16*tonumber('0x' .. cs[1]) + tonumber('0x' .. cs[1])
		local G = 16*tonumber('0x' .. cs[2]) + tonumber('0x' .. cs[2])
		local B = 16*tonumber('0x' .. cs[3]) + tonumber('0x' .. cs[3])

		return rgbdec2lum(R, G, B)
	end

	-- failure, return blank
	return ''
end

function p._greatercontrast(args)
	local bias = tonumber(args['bias'] or '0') or 0
	local v1 = color2lum(args[1] or '')
	local c2 = args[2] or '#FFFFFF'
	local v2 = color2lum(c2)
	local c3 = args[3] or '#000000'
	local v3 = color2lum(c3)
	local ratio1 = 0;
	local ratio2 = 0;
	if (type(v1) == 'number' and type(v2) == 'number') then
		ratio1 = (v2 + 0.05)/(v1 + 0.05)
		ratio1 = (ratio1 < 1) and 1/ratio1 or ratio1
	end
	if (type(v1) == 'number' and type(v3) == 'number') then
		ratio2 = (v3 + 0.05)/(v1 + 0.05)
		ratio2 = (ratio2 < 1) and 1/ratio2 or ratio2
	end
	return (ratio1 + bias > ratio2) and c2 or c3
end

function p._ratio(args)
	local v1 = color2lum(args[1])
	local v2 = color2lum(args[2])
	if (type(v1) == 'number' and type(v2) == 'number') then
		-- v1 should be the brighter of the two.
		if v2 > v1 then
			v1, v2 = v2, v1
		end
		return (v1 + 0.05)/(v2 + 0.05)
	else
		return args['error'] or '?'
	end
end

function p._styleratio(args)
	local style = (args[1] or ''):lower()
	local bg, fg = (args[2] or 'white'), (args[3] or 'black')

	local slist = mw.text.split(s or '', ';')
	for k = 1,#slist do
		s = slist[k]
		local k,v = s:match( '^[%s]*([^:]-):([^:]-)[%s;]*$' )
		k = k or ''
		v = v or ''
		if (k:match('^[%s]*(background)[%s]*$') or k:match('^[%s]*(background-color)[%s]*$')) then
			bg = v
		elseif (k:match('^[%s]*(color)[%s]*$')) then
			fg = v
		end
	end

	return p._ratio({bg, fg, ['error'] = args['error']})
end

function p.lum(frame)
	return color2lum(frame.args[1] or frame:getParent().args[1])
end

function p.ratio(frame)
	local args = frame.args[1] and frame.args or frame:getParent().args
	return p._ratio(args)
end

function p.styleratio(frame)
	local args = frame.args[1] and frame.args or frame:getParent().args
	return p._styleratio(args)
end

function p.greatercontrast(frame)
	local args = frame.args[1] and frame.args or frame:getParent().args
	return p._greatercontrast(args)
end

return p