[core] fix opacity interpolation for composition expressions (#15738)

port https://github.com/mapbox/mapbox-gl-js/pull/8818

1 files changed, 4 insertions, 5 deletions

diff --git a/src/mbgl/renderer/paint_property_binder.hpp b/src/mbgl/renderer/paint_property_binder.hpp
index 1a36f8a2e5..db9f61411a 100644
--- a/src/mbgl/renderer/paint_property_binder.hpp
+++ b/src/mbgl/renderer/paint_property_binder.hpp
@@ -370,11 +370,10 @@ public:
     }
 
     std::tuple<float> interpolationFactor(float currentZoom) const override {
-        if (expression.useIntegerZoom) {
-            return std::tuple<float> { expression.interpolationFactor(zoomRange, std::floor(currentZoom)) };
-        } else {
-            return std::tuple<float> { expression.interpolationFactor(zoomRange, currentZoom) };
-        }
+        const float possiblyRoundedZoom = expression.useIntegerZoom ? std::floor(currentZoom) : currentZoom;
+
+        return std::tuple<float>{
+            ::fmax(0.0, ::fmin(1.0, expression.interpolationFactor(zoomRange, possiblyRoundedZoom)))};
     }
 
     std::tuple<T> uniformValue(const PossiblyEvaluatedPropertyValue<T>& currentValue) const override {