From dfca8fb2149eea69e7cff08a15d964b4a5e4d710 Mon Sep 17 00:00:00 2001
From: Ansis Brammanis <ansis@mapbox.com>
Date: Wed, 2 Oct 2019 13:49:33 -0400
Subject: [core] fix opacity interpolation for composition expressions (#15738)

port https://github.com/mapbox/mapbox-gl-js/pull/8818
---
 platform/node/test/ignores.json             | 1 +
 src/mbgl/renderer/paint_property_binder.hpp | 9 ++++-----
 2 files changed, 5 insertions(+), 5 deletions(-)

diff --git a/platform/node/test/ignores.json b/platform/node/test/ignores.json
index f053b2add1..8da2905dbb 100644
--- a/platform/node/test/ignores.json
+++ b/platform/node/test/ignores.json
@@ -71,6 +71,7 @@
   "render-tests/circle-sort-key/literal": "https://github.com/mapbox/mapbox-gl-native/issues/15008",
   "render-tests/fill-sort-key/literal": "https://github.com/mapbox/mapbox-gl-native/issues/15008",
   "render-tests/line-sort-key/literal": "https://github.com/mapbox/mapbox-gl-native/issues/15008",
+  "render-tests/regressions/mapbox-gl-js#8817": "skip - https://github.com/mapbox/mapbox-gl-native/issues/15737",
   "query-tests/fill-extrusion/base-in": "https://github.com/mapbox/mapbox-gl-native/issues/13139",
   "query-tests/fill-extrusion/box-in": "https://github.com/mapbox/mapbox-gl-native/issues/13139",
   "query-tests/fill-extrusion/side-in": "https://github.com/mapbox/mapbox-gl-native/issues/13139",
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 {
-- 
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