[core] UnitBezier ctor is now constexpr

1 files changed, 19 insertions, 20 deletions

diff --git a/include/mbgl/util/unitbezier.hpp b/include/mbgl/util/unitbezier.hpp
index ce3e78f3cc..3a4994917b 100644
--- a/include/mbgl/util/unitbezier.hpp
+++ b/include/mbgl/util/unitbezier.hpp
@@ -31,32 +31,31 @@ namespace mbgl {
 namespace util {
 
 struct UnitBezier {
-    UnitBezier(double p1x, double p1y, double p2x, double p2y) {
-        // Calculate the polynomial coefficients, implicit first and last control points are (0,0) and (1,1).
-        cx = 3.0 * p1x;
-        bx = 3.0 * (p2x - p1x) - cx;
-        ax = 1.0 - cx - bx;
-
-        cy = 3.0 * p1y;
-        by = 3.0 * (p2y - p1y) - cy;
-        ay = 1.0 - cy - by;
+    // Calculate the polynomial coefficients, implicit first and last control points are (0,0) and (1,1).
+    constexpr UnitBezier(double p1x, double p1y, double p2x, double p2y)
+        : cx(3.0 * p1x)
+        , bx(3.0 * (p2x - p1x) - cx)
+        , ax(1.0 - cx - bx)
+        , cy(3.0 * p1y)
+        , by(3.0 * (p2y - p1y) - cy)
+        , ay(1.0 - cy - by) {
     }
 
-    double sampleCurveX(double t) {
+    double sampleCurveX(double t) const {
         // `ax t^3 + bx t^2 + cx t' expanded using Horner's rule.
         return ((ax * t + bx) * t + cx) * t;
     }
 
-    double sampleCurveY(double t) {
+    double sampleCurveY(double t) const {
         return ((ay * t + by) * t + cy) * t;
     }
 
-    double sampleCurveDerivativeX(double t) {
+    double sampleCurveDerivativeX(double t) const {
         return (3.0 * ax * t + 2.0 * bx) * t + cx;
     }
 
     // Given an x value, find a parametric value it came from.
-    double solveCurveX(double x, double epsilon) {
+    double solveCurveX(double x, double epsilon) const {
         double t0;
         double t1;
         double t2;
@@ -100,18 +99,18 @@ struct UnitBezier {
         return t2;
     }
 
-    double solve(double x, double epsilon) {
+    double solve(double x, double epsilon) const {
         return sampleCurveY(solveCurveX(x, epsilon));
     }
 
 private:
-    double ax;
-    double bx;
-    double cx;
+    const double cx;
+    const double bx;
+    const double ax;
 
-    double ay;
-    double by;
-    double cy;
+    const double cy;
+    const double by;
+    const double ay;
 };
 
 } // namespace util