Module:Color contrast

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Revision as of 11:22, 25 July 2015 by Mr. Stradivarius (talk) (split the color data out to Module:Color contrast/colors and load it with mw.loadData - this way we only create the table once per page rather than every time color2lum is called)
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Documentation for this module may be created at Module:Color contrast/doc

--
-- 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 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
	-- 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 = sRGB( (16*tonumber('0x' .. cs[1]) + tonumber('0x' .. cs[2]))/255 )
		local G = sRGB( (16*tonumber('0x' .. cs[3]) + tonumber('0x' .. cs[4]))/255 )
		local B = sRGB( (16*tonumber('0x' .. cs[5]) + tonumber('0x' .. cs[6]))/255 )

		L = 0.2126 * R + 0.7152 * G + 0.0722 * B
		return L
	elseif ( #cs == 3 ) then
		local R = sRGB( (16*tonumber('0x' .. cs[1]) + tonumber('0x' .. cs[1]))/255 )
		local G = sRGB( (16*tonumber('0x' .. cs[2]) + tonumber('0x' .. cs[2]))/255 )
		local B = sRGB( (16*tonumber('0x' .. cs[3]) + tonumber('0x' .. cs[3]))/255 )

		L = 0.2126 * R + 0.7152 * G + 0.0722 * B
		return L
	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.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.greatercontrast(frame)
	local args = frame.args[1] and frame.args or frame:getParent().args
	return p._greatercontrast(args)
end

return p