From 3ab40611a51e1917c1aea395b44e5efc91e3359e Mon Sep 17 00:00:00 2001
From: Ansis Brammanis <ansis@mapbox.com>
Date: Tue, 1 Oct 2019 15:53:31 -0400
Subject: [PATCH] [core] fix opacity interpolation for composition expressions

port https://github.com/mapbox/mapbox-gl-js/pull/8818
---
 platform/node/test/ignores.json             |  1 +
 src/mbgl/renderer/paint_property_binder.hpp | 10 +++++-----
 2 files changed, 6 insertions(+), 5 deletions(-)

diff --git a/platform/node/test/ignores.json b/platform/node/test/ignores.json
index f053b2add1e..8da2905dbb0 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 1a36f8a2e58..402827de3c2 100644
--- a/src/mbgl/renderer/paint_property_binder.hpp
+++ b/src/mbgl/renderer/paint_property_binder.hpp
@@ -370,11 +370,11 @@ class CompositeFunctionPaintPropertyBinder final : public PaintPropertyBinder<T,
     }
 
     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> { std::fmax(0.0, std::fmin(1.0, expression.interpolationFactor(zoomRange, possiblyRoundedZoom))) };
     }
 
     std::tuple<T> uniformValue(const PossiblyEvaluatedPropertyValue<T>& currentValue) const override {