[core] Add `line-gradient` property

Porting of https://github.com/mapbox/mapbox-gl-js/pull/6303
See the link above for the description of the feature and
its limitations).

Based on patch from @lbud (Lauren Budorick).

1 files changed, 7 insertions, 2 deletions

diff --git a/src/mbgl/renderer/buckets/line_bucket.hpp b/src/mbgl/renderer/buckets/line_bucket.hpp
index 8fe7184941..23d30ca416 100644
--- a/src/mbgl/renderer/buckets/line_bucket.hpp
+++ b/src/mbgl/renderer/buckets/line_bucket.hpp
@@ -47,12 +47,17 @@ private:
         TriangleElement(uint16_t a_, uint16_t b_, uint16_t c_) : a(a_), b(b_), c(c_) {}
         uint16_t a, b, c;
     };
+
+    class Distances;
     void addCurrentVertex(const GeometryCoordinate& currentVertex, double& distance,
             const Point<double>& normal, double endLeft, double endRight, bool round,
-            std::size_t startVertex, std::vector<LineBucket::TriangleElement>& triangleStore);
+            std::size_t startVertex, std::vector<LineBucket::TriangleElement>& triangleStore,
+            optional<Distances> distances);
+
     void addPieSliceVertex(const GeometryCoordinate& currentVertex, double distance,
             const Point<double>& extrude, bool lineTurnsLeft, std::size_t startVertex,
-            std::vector<TriangleElement>& triangleStore);
+            std::vector<TriangleElement>& triangleStore,
+            optional<Distances> distances);
 
     std::ptrdiff_t e1;
     std::ptrdiff_t e2;