Below are two functions on base of the ones mentioned in the
W3C's Accessibility Recommendations. They work fine here for me.
To test these, I made a stack for the Raspi collection in the forum.
This stack contains also a _simple_ algorithm for _trying_ to get a
textColor on base of the current textColor (the current backColor
is fixed) such that a contrast ratio of at least 7 is reached.
Works for giving an "advice" in most cases I tried. The algorithm
may easily be improved (for example by giving the change of color
channels different weights, adaptive, on base of input).
-- usage example
on mouseUp
lock screen; lock messages
put the backColor of fld "Text" into bC
put the backColor of fld "Text" into fC
put relativeLuminance(bC) into bL
put relativeLuminance(fC) into fL
put contrastRatio(bL,fL) into contrastBF
put "Contrast Ratio: " & round(contrastBF,2) into fld "contrastRatio"
unlock screen; unlock messages
end mouseUp
-- param RGB is of the form "r,g,b" where each
-- item r,g,b is an integer in range 0-255
function relativeLuminance RGB
put 0 into tLuminance
put "0.2126,0.7152,0.0722" into tWeights
repeat with i=1 to 3
put item i of RGB into ci
put ci/255 into cc
if cc <= 0.03928 then
put cc/12.92 into ri
else
put ((cc+0.055)/1.055)^2.4 into ri
end if
add (item i of tWeights*ri) to tLuminance
end repeat
return tLuminance
end relativeLuminance
-- computes ratio of lighter against darker r.L.
function contrastRatio lu1,lu2
if lu1 > lu2 then -- lu2 is darker
return (lu1 + 0.05) / (lu2 + 0.05)
else return (lu2 + 0.05) / (lu1 + 0.05)
end contrastRatio
_______________________________________________
use-livecode mailing list
use-livecode@lists.runrev.com
Please visit this url to subscribe, unsubscribe and manage your subscription
preferences:
http://lists.runrev.com/mailman/listinfo/use-livecode
