Add a contrast function

lib/less/functions.js

@@ -44,6 +44,12 @@ tree.functions = {
     alpha: function (color) {
         return new(tree.Dimension)(color.toHSL().a);
     },
+    luma: function (color) {
+        return new(tree.Dimension)(Math.round((0.2126 * (color.rgb[0]/255) +
+            0.7152 * (color.rgb[1]/255) +
+            0.0722 * (color.rgb[2]/255))
+            * color.alpha * 100), '%');
+    },
     saturate: function (color, amount) {
         var hsl = color.toHSL();
 
@@ -124,6 +130,24 @@ tree.functions = {
     greyscale: function (color) {
         return this.desaturate(color, new(tree.Dimension)(100));
     },
+    contrast: function (color, dark, light, threshold) {
+        if (typeof light === 'undefined') {
+            light = this.rgba(255, 255, 255, 1.0);
+        }
+        if (typeof dark === 'undefined') {
+            dark = this.rgba(0, 0, 0, 1.0);
+        }
+        if (typeof threshold === 'undefined') {
+            threshold = 0.43;
+        } else {
+            threshold = threshold.value;
+        }
+        if (((0.2126 * (color.rgb[0]/255) + 0.7152 * (color.rgb[1]/255) + 0.0722 * (color.rgb[2]/255)) * color.alpha) < threshold) {
+            return light;
+        } else {
+            return dark;
+        }
+    },
     e: function (str) {
         return new(tree.Anonymous)(str instanceof tree.JavaScript ? str.evaluated : str);
     },

test/css/functions.css

@@ -14,6 +14,27 @@
   greyscale: #2e2e2e;
   spin-p: #bf6a40;
   spin-n: #bf4055;
+  luma-white: 100%;
+  luma-black: 0%;
+  luma-red: 21%;
+  luma-green: 72%;
+  luma-blue: 7%;
+  luma-yellow: 93%;
+  luma-cyan: 79%;
+  luma-white-alpha: 50%;
+  contrast-white: #000000;
+  contrast-black: #ffffff;
+  contrast-red: #ffffff;
+  contrast-green: #000000;
+  contrast-blue: #ffffff;
+  contrast-yellow: #000000;
+  contrast-cyan: #000000;
+  contrast-light: #111111;
+  contrast-dark: #eeeeee;
+  contrast-light-thresh: #111111;
+  contrast-dark-thresh: #eeeeee;
+  contrast-high-thresh: #eeeeee;
+  contrast-low-thresh: #111111;
   format: "rgb(32, 128, 64)";
   format-string: "hello world";
   format-multiple: "hello earth 2";

test/less/functions.less

@@ -17,6 +17,28 @@
   greyscale: greyscale(#203c31);
   spin-p: spin(hsl(340, 50%, 50%), 40);
   spin-n: spin(hsl(30, 50%, 50%), -40);
+  luma-white: luma(#fff);
+  luma-black: luma(#000);
+  luma-black-alpha: luma(rgba(0,0,0,0.5));
+  luma-red: luma(#ff0000);
+  luma-green: luma(#00ff00);
+  luma-blue: luma(#0000ff);
+  luma-yellow: luma(#ffff00);
+  luma-cyan: luma(#00ffff);
+  luma-white-alpha: luma(rgba(255,255,255,0.5));
+  contrast-white: contrast(#fff);
+  contrast-black: contrast(#000);
+  contrast-red: contrast(#ff0000);
+  contrast-green: contrast(#00ff00);
+  contrast-blue: contrast(#0000ff);
+  contrast-yellow: contrast(#ffff00);
+  contrast-cyan: contrast(#00ffff);
+  contrast-light: contrast(#fff, #111111, #eeeeee);
+  contrast-dark: contrast(#000, #111111, #eeeeee);
+  contrast-light-thresh: contrast(#fff, #111111, #eeeeee, 0.5);
+  contrast-dark-thresh: contrast(#000, #111111, #eeeeee, 0.5);
+  contrast-high-thresh: contrast(#555, #111111, #eeeeee, 0.6);
+  contrast-low-thresh: contrast(#555, #111111, #eeeeee, 0.1);
   format: %("rgb(%d, %d, %d)", @r, 128, 64);
   format-string: %("hello %s", "world");
   format-multiple: %("hello %s %d", "earth", 2);