Make location indicator bearing a paint property

This change introduces a new property type, Rotation, that uses
a custom interpolator, and that is currently applied to
all style properties named "bearing", with a period attribute.

1 files changed, 24 insertions, 2 deletions

diff --git a/include/mbgl/util/interpolate.hpp b/include/mbgl/util/interpolate.hpp
index aff730a0a2..566f2b0a6b 100644
--- a/include/mbgl/util/interpolate.hpp
+++ b/include/mbgl/util/interpolate.hpp
@@ -1,9 +1,10 @@
 #pragma once
 
+#include <mbgl/style/expression/value.hpp>
+#include <mbgl/style/position.hpp>
+#include <mbgl/style/rotation.hpp>
 #include <mbgl/util/color.hpp>
 #include <mbgl/util/range.hpp>
-#include <mbgl/style/position.hpp>
-#include <mbgl/style/expression/value.hpp>
 
 #include <array>
 #include <vector>
@@ -102,6 +103,27 @@ public:
     }
 };
 
+template <>
+struct Interpolator<style::Rotation> {
+public:
+    style::Rotation operator()(const style::Rotation& a, const style::Rotation& b, const double t) {
+        assert(a.period() == b.period());
+        auto period = a.period();
+        auto aAngle = std::fmod(a.getAngle(), period);
+        auto bAngle = std::fmod(b.getAngle(), period);
+
+        if (aAngle - bAngle > period * 0.5) {
+            return {std::fmod(aAngle * (1.0 - t) + (bAngle + period) * t, period)};
+        }
+
+        if (aAngle - bAngle < period * -0.5) {
+            return {std::fmod((aAngle + period) * (1.0 - t) + bAngle * t, period)};
+        }
+
+        return {aAngle * (1.0 - t) + bAngle * t};
+    }
+};
+
 struct Uninterpolated {
     template <class T>
     T operator()(const T& a, const T&, const double) const {