From 8b8f6bfbeebf500294332ab0f73f4ef7580c9ea2 Mon Sep 17 00:00:00 2001
From: Natalie Weizenbaum <nex342@gmail.com>
Date: Wed, 21 Sep 2016 13:56:23 -0700
Subject: [PATCH] Add opacify() et al

---
 lib/src/functions.dart | 21 +++++++++++++++++++++
 1 file changed, 21 insertions(+)

diff --git a/lib/src/functions.dart b/lib/src/functions.dart
index d8a399ef..44c9cefa 100644
--- a/lib/src/functions.dart
+++ b/lib/src/functions.dart
@@ -222,6 +222,13 @@ void defineCoreFunctions(Environment environment) {
     return new SassNumber(color.alpha);
   }));
 
+  environment.setFunction(new BuiltInCallable("opacify", r"$color", _opacify));
+  environment.setFunction(new BuiltInCallable("fade-in", r"$color", _opacify));
+  environment.setFunction(
+      new BuiltInCallable("transparentize", r"$color", _transparentize));
+  environment
+      .setFunction(new BuiltInCallable("fade-out", r"$color", _transparentize));
+
   // ## Introspection
 
   environment.setFunction(new BuiltInCallable("inspect", r"$value",
@@ -280,3 +287,17 @@ SassColor _mix(SassColor color1, SassColor color2, SassNumber weight) {
       (color1.blue * weight1 + color2.blue * weight2).round(),
       color1.alpha * weightScale + color2.alpha * (1 - weightScale));
 }
+
+SassColor _opacify(List<Value> arguments) {
+  var color = arguments[0].assertColor("color");
+  var amount = arguments[1].assertNumber("amount");
+
+  return color.changeAlpha(color.alpha + amount.valueInRange(0, 1, "amount"));
+}
+
+SassColor _transparentize(List<Value> arguments) {
+  var color = arguments[0].assertColor("color");
+  var amount = arguments[1].assertNumber("amount");
+
+  return color.changeAlpha(color.alpha - amount.valueInRange(0, 1, "amount"));
+}