[core] use constexpr constants

1 files changed, 28 insertions, 17 deletions

diff --git a/include/mbgl/util/constants.hpp b/include/mbgl/util/constants.hpp
index 5bfb252bce..c49b1ab9df 100644
--- a/include/mbgl/util/constants.hpp
+++ b/include/mbgl/util/constants.hpp
@@ -11,23 +11,34 @@ namespace mbgl {
 
 namespace util {
 
-extern const float tileSize;
-extern const int32_t EXTENT;
-
-extern const double DEG2RAD;
-extern const double RAD2DEG;
-extern const double M2PI;
-extern const double EARTH_RADIUS_M;
-extern const double LATITUDE_MAX;
-extern const double LONGITUDE_MAX;
-extern const double DEGREES_MAX;
-extern const double PITCH_MAX;
-extern const double MIN_ZOOM;
-extern const double MAX_ZOOM;
-
-extern const uint64_t DEFAULT_MAX_CACHE_SIZE;
-
-extern const SystemDuration CLOCK_SKEW_RETRY_TIMEOUT;
+constexpr float tileSize = 512;
+
+/*
+ * The maximum extent of a feature that can be safely stored in the buffer.
+ * In practice, all features are converted to this extent before being added.
+ *
+ * Positions are stored as signed 16bit integers.
+ * One bit is lost for signedness to support featuers extending past the left edge of the tile.
+ * One bit is lost because the line vertex buffer packs 1 bit of other data into the int.
+ * One bit is lost to support features extending past the extent on the right edge of the tile.
+ * This leaves us with 2^13 = 8192
+ */
+constexpr int32_t EXTENT = 8192;
+
+constexpr double DEG2RAD = M_PI / 180.0;
+constexpr double RAD2DEG = 180.0 / M_PI;
+constexpr double M2PI = M_PI * 2;
+constexpr double EARTH_RADIUS_M = 6378137;
+constexpr double LATITUDE_MAX = 85.051128779806604;
+constexpr double LONGITUDE_MAX = 180;
+constexpr double DEGREES_MAX = 360;
+constexpr double PITCH_MAX = M_PI / 3;
+constexpr double MIN_ZOOM = 0.0;
+constexpr double MAX_ZOOM = 25.5;
+
+constexpr uint64_t DEFAULT_MAX_CACHE_SIZE = 50 * 1024 * 1024;;
+
+constexpr SystemDuration CLOCK_SKEW_RETRY_TIMEOUT = Seconds(30);
 
 } // namespace util