complete redesign: use nodejs on server instead of php - documentation to be updated

nodejs/node_modules/stylus/lib/functions/transparentify.js

@@ -0,0 +1,63 @@
+var utils = require('../utils')
+  , nodes = require('../nodes');
+
+/**
+ * Returns the transparent version of the given `top` color,
+ * as if it was blend over the given `bottom` color.
+ *
+ * Examples:
+ *
+ *     transparentify(#808080)
+ *     => rgba(0,0,0,0.5)
+ *
+ *     transparentify(#414141, #000)
+ *     => rgba(255,255,255,0.25)
+ *
+ *     transparentify(#91974C, #F34949, 0.5)
+ *     => rgba(47,229,79,0.5)
+ *
+ * @param {RGBA|HSLA} top
+ * @param {RGBA|HSLA} [bottom=#fff]
+ * @param {Unit} [alpha]
+ * @return {RGBA}
+ * @api public
+ */
+
+module.exports = function transparentify(top, bottom, alpha){
+  utils.assertColor(top);
+  top = top.rgba;
+  // Handle default arguments
+  bottom = bottom || new nodes.RGBA(255, 255, 255, 1);
+  if (!alpha && bottom && !bottom.rgba) {
+    alpha = bottom;
+    bottom = new nodes.RGBA(255, 255, 255, 1);
+  }
+  utils.assertColor(bottom);
+  bottom = bottom.rgba;
+  var bestAlpha = ['r', 'g', 'b'].map(function(channel){
+    return (top[channel] - bottom[channel]) / ((0 < (top[channel] - bottom[channel]) ? 255 : 0) - bottom[channel]);
+  }).sort(function(a, b){return a < b;})[0];
+  if (alpha) {
+    utils.assertType(alpha, 'unit', 'alpha');
+    if ('%' == alpha.type) {
+      bestAlpha = alpha.val / 100;
+    } else if (!alpha.type) {
+      bestAlpha = alpha = alpha.val;
+    }
+  }
+  bestAlpha = Math.max(Math.min(bestAlpha, 1), 0);
+  // Calculate the resulting color
+  function processChannel(channel) {
+    if (0 == bestAlpha) {
+      return bottom[channel]
+    } else {
+      return bottom[channel] + (top[channel] - bottom[channel]) / bestAlpha
+    }
+  }
+  return new nodes.RGBA(
+    processChannel('r'),
+    processChannel('g'),
+    processChannel('b'),
+    Math.round(bestAlpha * 100) / 100
+  );
+}