From c231191dbc6f055341fd25ce97309614dc52802f Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Minh=20Nguye=CC=82=CC=83n?= <mxn@1ec5.org>
Date: Thu, 29 Mar 2018 12:55:29 -0700
Subject: [core] Round-trip linear interpolators

---
 mapbox-gl-js                              |  2 +-
 src/mbgl/style/conversion/stringify.hpp   | 20 ++++++++++++++------
 src/mbgl/style/expression/interpolate.cpp |  6 +++++-
 test/style/conversion/stringify.test.cpp  |  2 ++
 4 files changed, 22 insertions(+), 8 deletions(-)

diff --git a/mapbox-gl-js b/mapbox-gl-js
index 8a19f60799..34902f8db3 160000
--- a/mapbox-gl-js
+++ b/mapbox-gl-js
@@ -1 +1 @@
-Subproject commit 8a19f6079933817fd73eed71159130b8ac53a00f
+Subproject commit 34902f8db3f8a3757a465d62a96b8fa731ee1461
diff --git a/src/mbgl/style/conversion/stringify.hpp b/src/mbgl/style/conversion/stringify.hpp
index 7924a442c4..9e16d8b2c6 100644
--- a/src/mbgl/style/conversion/stringify.hpp
+++ b/src/mbgl/style/conversion/stringify.hpp
@@ -303,9 +303,13 @@ public:
     template <class T>
     void operator()(const ExponentialStops<T>& f) {
         writer.Key("type");
-        writer.String("exponential");
-        writer.Key("base");
-        writer.Double(f.base);
+        if (f.base == 1) {
+            writer.String("linear");
+        } else {
+            writer.String("exponential");
+            writer.Key("base");
+            writer.Double(f.base);
+        }
         writer.Key("stops");
         stringifyStops(f.stops);
     }
@@ -335,9 +339,13 @@ public:
     template <class T>
     void operator()(const CompositeExponentialStops<T>& f) {
         writer.Key("type");
-        writer.String("exponential");
-        writer.Key("base");
-        writer.Double(f.base);
+        if (f.base == 1) {
+            writer.String("linear");
+        } else {
+            writer.String("exponential");
+            writer.Key("base");
+            writer.Double(f.base);
+        }
         writer.Key("stops");
         stringifyCompositeStops(f.stops);
     }
diff --git a/src/mbgl/style/expression/interpolate.cpp b/src/mbgl/style/expression/interpolate.cpp
index 30b2cba81b..daad8523f2 100644
--- a/src/mbgl/style/expression/interpolate.cpp
+++ b/src/mbgl/style/expression/interpolate.cpp
@@ -223,7 +223,11 @@ mbgl::Value Interpolate<T>::serialize() const {
     
     interpolator.match(
         [&](const ExponentialInterpolator& exponential) {
-            serialized.emplace_back(std::vector<mbgl::Value>{{ std::string("exponential"), exponential.base }});
+            if (exponential.base == 1) {
+                serialized.emplace_back(std::vector<mbgl::Value>{{ std::string("linear") }});
+            } else {
+                serialized.emplace_back(std::vector<mbgl::Value>{{ std::string("exponential"), exponential.base }});
+            }
         },
         [&](const CubicBezierInterpolator& cubicBezier) {
             static const std::string cubicBezierTag("cubic-bezier");
diff --git a/test/style/conversion/stringify.test.cpp b/test/style/conversion/stringify.test.cpp
index 0b2940a0e0..06349c9388 100644
--- a/test/style/conversion/stringify.test.cpp
+++ b/test/style/conversion/stringify.test.cpp
@@ -80,6 +80,8 @@ TEST(Stringify, Filter) {
 }
 
 TEST(Stringify, CameraFunction) {
+    ASSERT_EQ(stringify(CameraFunction<float>(ExponentialStops<float> { {{0, 1}}, 1 })),
+        "{\"type\":\"linear\",\"stops\":[[0.0,1.0]]}");
     ASSERT_EQ(stringify(CameraFunction<float>(ExponentialStops<float> { {{0, 1}}, 2 })),
         "{\"type\":\"exponential\",\"base\":2.0,\"stops\":[[0.0,1.0]]}");
     ASSERT_EQ(stringify(CameraFunction<float>(IntervalStops<float> { {{0, 1}} })),
-- 
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