[core] Fix cubic-bezier interpolation for zooms outside stop range.

Fixes issue #12812. Using `util::interpolationFactor` handles the case where inputLevels.min == inputLevels.max, so it returns an interpolation factor of "0" instead of dividing by 0.
mapbox · Sep 6, 2018 · dbcbac4 · dbcbac4
1 parent 3e23cae
commit dbcbac4
Showing 1 changed file with 7 additions and 1 deletion.
diff --git a/include/mbgl/style/expression/interpolator.hpp b/include/mbgl/style/expression/interpolator.hpp
@@ -33,7 +33,13 @@ class CubicBezierInterpolator {
     CubicBezierInterpolator(double x1_, double y1_, double x2_, double y2_) : ub(x1_, y1_, x2_, y2_) {}
 
     double interpolationFactor(const Range<double>& inputLevels, const double input) const {
-        return ub.solve(input / (inputLevels.max - inputLevels.min), 1e-6);
+        return ub.solve(util::interpolationFactor(1.0,
+                                                  Range<float> {
+                                                      static_cast<float>(inputLevels.min),
+                                                      static_cast<float>(inputLevels.max)
+                                                  },
+                                                  input),
+                        1e-6);
     }
 
     bool operator==(const CubicBezierInterpolator& rhs) const {