From 105621c67593dd3036e19da0033480f32ffa1655 Mon Sep 17 00:00:00 2001
From: John Firebaugh <john.firebaugh@gmail.com>
Date: Thu, 14 Dec 2017 13:41:08 -0800
Subject: [PATCH] Use toString() for to-string implementation; fix
 premultiplication bugs

---
 src/style-spec/expression/definitions/index.js    |  8 ++++----
 .../expression-tests/to-rgba/alpha/test.json      | 15 +++++++++++++++
 2 files changed, 19 insertions(+), 4 deletions(-)
 create mode 100644 test/integration/expression-tests/to-rgba/alpha/test.json

diff --git a/src/style-spec/expression/definitions/index.js b/src/style-spec/expression/definitions/index.js
index e398d409de6..38388b19a1b 100644
--- a/src/style-spec/expression/definitions/index.js
+++ b/src/style-spec/expression/definitions/index.js
@@ -57,10 +57,10 @@ function rgba(ctx, [r, g, b, a]) {
     r = r.evaluate(ctx);
     g = g.evaluate(ctx);
     b = b.evaluate(ctx);
-    a = a && a.evaluate(ctx);
+    a = a ? a.evaluate(ctx) : 1;
     const error = validateRGBA(r, g, b, a);
     if (error) throw new RuntimeError(error);
-    return new Color(r / 255, g / 255, b / 255, a);
+    return new Color(r / 255 * a, g / 255 * a, b / 255 * a, a);
 }
 
 function has(key, obj) {
@@ -101,7 +101,7 @@ CompoundExpression.register(expressions, {
             if (v === null || type === 'string' || type === 'number' || type === 'boolean') {
                 return String(v);
             } else if (v instanceof Color) {
-                return `rgba(${v.r * 255},${v.g * 255},${v.b * 255},${v.a})`;
+                return v.toString();
             } else {
                 return JSON.stringify(v);
             }
@@ -117,7 +117,7 @@ CompoundExpression.register(expressions, {
         [ColorType],
         (ctx, [v]) => {
             const {r, g, b, a} = v.evaluate(ctx);
-            return [255 * r, 255 * g, 255 * b, a];
+            return [255 * r / a, 255 * g / a, 255 * b / a, a];
         }
     ],
     'rgb': [
diff --git a/test/integration/expression-tests/to-rgba/alpha/test.json b/test/integration/expression-tests/to-rgba/alpha/test.json
new file mode 100644
index 00000000000..56656a7adf2
--- /dev/null
+++ b/test/integration/expression-tests/to-rgba/alpha/test.json
@@ -0,0 +1,15 @@
+{
+  "expression": ["to-rgba", ["rgba", 0, 128, 255, 0.5]],
+  "inputs": [
+    [{}, {}]
+  ],
+  "expected": {
+    "outputs": [[0, 128, 255, 0.5]],
+    "compiled": {
+      "result": "success",
+      "isZoomConstant": true,
+      "isFeatureConstant": true,
+      "type": "array<number, 4>"
+    }
+  }
+}