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add rgba contrast checking by converting rgba to a solid rgb color #97

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add rgba contrast checking by converting rgba to a solid rgb color #97

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3a4305b
Merge remote-tracking branch 'yargalot/master'
mfairchild365 Apr 29, 2014
247b864
Merge remote-tracking branch 'yargalot/master'
mfairchild365 Jun 26, 2014
772f653
Merge branch 'alpha-index'
mfairchild365 Jun 26, 2014
afc99ba
Add methods to convert an rgba background color to rgb
mfairchild365 Jun 27, 2014
b3d28fc
Convert rgba to a solid color before checking contrast
mfairchild365 Jun 27, 2014
b8d7684
Don't warn about rgba anymore
mfairchild365 Jun 27, 2014
eaa1309
Convert to a colour string
mfairchild365 Jun 27, 2014
e2159c5
Return rgb channels as %
mfairchild365 Jun 27, 2014
e730b35
Allow checking against any rgba color, not just the background
mfairchild365 Jun 27, 2014
36c217f
Also convert the foreground (text) rgba color
mfairchild365 Jun 27, 2014
b8d4fa5
Merge remote-tracking branch 'squizlabs/master' into alpha-checking
mfairchild365 Jun 27, 2014
7ce911b
Correctly calculate layered transparencies
mfairchild365 Jun 27, 2014
203031f
Assume a white background if no solid colors were found
mfairchild365 Jul 9, 2014
338cd1d
Include an alpha
mfairchild365 Jul 9, 2014
30790df
Merge remote-tracking branch 'squizlabs/master' into alpha-checking
mfairchild365 Nov 7, 2014
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85 changes: 83 additions & 2 deletions HTMLCS.js
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Original file line number Diff line number Diff line change
Expand Up @@ -851,6 +851,82 @@ var HTMLCS = new function()
return lum;
}

/**
* Convert an rgba colour to rgb, by traversing the dom and mixing colors as needed.
*
* @param element - the element to compare the rgba color against.
* @param colour - the starting rgba color to check.
* @returns {Colour Object}
*/
this.rgbaBackgroundToRgb = function(colour, element) {
var parent = element.parentNode;
var original = this.colourStrToRGB(colour);
var backgrounds = [];
var solidFound = false;

if (original.alpha == 1) {
//Return early if it is already solid.
return original;
}

//Find all the background with transparancy until we get to a solid colour
while (solidFound == false) {
if ((!parent) || (!parent.ownerDocument)) {
//No parent was found, assume a solid white background.
backgrounds.push({
red: 1,
green: 1,
blue: 1,
alpha: 1
});
break;
}

var parentStyle = this.style(parent);
var parentColourStr = parentStyle.backgroundColor;
var parentColour = this.colourStrToRGB(parentColourStr);

if ((parentColourStr === 'transparent') || (parentColourStr === 'rgba(0, 0, 0, 0)')) {
//Skip totally transparent parents until we find a solid color.
parent = parent.parentNode;
continue;
}

backgrounds.push(parentColour);

if (parentColour.alpha == 1) {
solidFound = true;
}

parent = parent.parentNode;
}

//Now we need to start with the solid color that we found, and work our way up to the original color.
var solidColour = backgrounds.pop();
while (backgrounds.length) {
solidColour = this.mixColours(solidColour, backgrounds.pop());
}

return this.mixColours(solidColour, original);
}

this.mixColours = function(bg, fg) {
//Convert colors to int values for mixing.
bg.red = Math.round(bg.red*255);
bg.green = Math.round(bg.green*255);
bg.blue = Math.round(bg.blue*255);
fg.red = Math.round(fg.red*255);
fg.green = Math.round(fg.green*255);
fg.blue = Math.round(fg.blue*255);

return {
red: Math.round(fg.alpha * fg.red + (1 - fg.alpha) * bg.red) / 255,
green: Math.round(fg.alpha * fg.green + (1 - fg.alpha) * bg.green) / 255,
blue: Math.round(fg.alpha * fg.blue + (1 - fg.alpha) * bg.blue) / 255,
alpha: bg.alpha
}
}

/**
* Convert a colour string to a structure with red/green/blue elements.
*
Expand All @@ -871,7 +947,11 @@ var HTMLCS = new function()
colour = {
red: (matches[1] / 255),
green: (matches[2] / 255),
blue: (matches[3] / 255)
blue: (matches[3] / 255),
alpha: 1
}
if (matches[4]) {
colour.alpha = parseFloat(/^,\s*(.*)$/.exec(matches[4])[1]);
}
} else {
// Hex digit format.
Expand All @@ -886,7 +966,8 @@ var HTMLCS = new function()
colour = {
red: (parseInt(colour.substr(0, 2), 16) / 255),
green: (parseInt(colour.substr(2, 2), 16) / 255),
blue: (parseInt(colour.substr(4, 2), 16) / 255)
blue: (parseInt(colour.substr(4, 2), 16) / 255),
alpha: 1
};
}

Expand Down
3 changes: 3 additions & 0 deletions Standards/WCAG2AAA/Sniffs/Principle1/Guideline1_4/1_4_3.js
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Original file line number Diff line number Diff line change
Expand Up @@ -77,6 +77,9 @@ var HTMLCS_WCAG2AAA_Sniffs_Principle1_Guideline1_4_1_4_3 = {
if (isAbsolute === true) {
code += '.Abs';
HTMLCS.addMessage(HTMLCS.WARNING, element, 'This element is absolutely positioned and the background color can not be determined. Ensure the contrast ratio between the text and all covered parts of the background are at least ' + required + ':1.', code);
} else if (bgColour && bgColour.indexOf('rgba') === 0) {
code += '.Alpha';
HTMLCS.addMessage(HTMLCS.WARNING, element, 'This element\'s text is placed on a background that has an alpha transparency. Ensure the contrast ratio between the text and background color are at least ' + required + ':1.', code);
} else if (hasBgImg === true) {
code += '.BgImage';
HTMLCS.addMessage(HTMLCS.WARNING, element, 'This element\'s text is placed on a background image. Ensure the contrast ratio between the text and all covered parts of the image are at least ' + required + ':1.', code);
Expand Down
20 changes: 15 additions & 5 deletions Standards/WCAG2AAA/Sniffs/Principle1/Guideline1_4/1_4_3_Contrast.js
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Original file line number Diff line number Diff line change
Expand Up @@ -52,8 +52,8 @@ var HTMLCS_WCAG2AAA_Sniffs_Principle1_Guideline1_4_1_4_3_Contrast = {
var bgElement = node;
var hasBgImg = false;
var isAbsolute = false;
if (style.backgroundImage !== 'none') {

if (style.backgroundImage !== 'none') {
hasBgImg = true;
}

Expand Down Expand Up @@ -86,6 +86,7 @@ var HTMLCS_WCAG2AAA_Sniffs_Principle1_Guideline1_4_1_4_3_Contrast = {

var parentStyle = HTMLCS.util.style(parent);
var bgColour = parentStyle.backgroundColor;
var bgElement = parent;
if (parentStyle.backgroundImage !== 'none') {
hasBgImg = true;
}
Expand All @@ -96,12 +97,20 @@ var HTMLCS_WCAG2AAA_Sniffs_Principle1_Guideline1_4_1_4_3_Contrast = {
parent = parent.parentNode;
}//end while

if (bgColour && bgColour.indexOf('rgba') === 0) {
bgColour = HTMLCS.util.RGBtoColourStr(HTMLCS.util.rgbaBackgroundToRgb(bgColour, bgElement));
}

if (foreColour && foreColour.indexOf('rgba') === 0) {
foreColour = HTMLCS.util.RGBtoColourStr(HTMLCS.util.rgbaBackgroundToRgb(foreColour, node));
}

if (hasBgImg === true) {
// If we have a background image, skip the contrast ratio checks,
// and push a warning instead.
failures.push({
element: node,
colour: style.color,
colour: foreColour,
bgColour: undefined,
value: undefined,
required: reqRatio,
Expand All @@ -117,19 +126,20 @@ var HTMLCS_WCAG2AAA_Sniffs_Principle1_Guideline1_4_1_4_3_Contrast = {
required: reqRatio,
isAbsolute: true
});
continue;
} else if ((bgColour === 'transparent') || (bgColour === 'rgba(0, 0, 0, 0)')) {
// If the background colour is still transparent, this is probably
// a fragment with which we cannot reliably make a statement about
// contrast ratio. Skip the element.
continue;
}

var contrastRatio = HTMLCS.util.contrastRatio(bgColour, style.color);
var contrastRatio = HTMLCS.util.contrastRatio(bgColour, foreColour);



if (contrastRatio < reqRatio) {
var recommendation = this.recommendColour(bgColour, style.color, reqRatio);
var recommendation = this.recommendColour(bgColour, foreColour, reqRatio);

failures.push({
element: node,
Expand Down