From 4a5dc37245d23805d13865f5ef9c5f26e539a9ca Mon Sep 17 00:00:00 2001
From: Molly Lloyd <molly@mapbox.com>
Date: Thu, 14 Jun 2018 14:35:39 -0700
Subject: [core] Implement CrossFadedDataDrivenProperty to add support for
 feature expressions in `*-pattern` properties

---
 src/mbgl/renderer/property_evaluation_parameters.hpp | 19 +++++++++++++++++++
 1 file changed, 19 insertions(+)

(limited to 'src/mbgl/renderer/property_evaluation_parameters.hpp')

diff --git a/src/mbgl/renderer/property_evaluation_parameters.hpp b/src/mbgl/renderer/property_evaluation_parameters.hpp
index da6a4a0892..0e1c317294 100644
--- a/src/mbgl/renderer/property_evaluation_parameters.hpp
+++ b/src/mbgl/renderer/property_evaluation_parameters.hpp
@@ -5,6 +5,13 @@
 
 namespace mbgl {
 
+class CrossfadeParameters {
+public:
+    float fromScale;
+    float toScale;
+    float t;
+};
+
 class PropertyEvaluationParameters {
 public:
     explicit PropertyEvaluationParameters(float z_)
@@ -24,6 +31,18 @@ public:
           defaultFadeDuration(std::move(defaultFadeDuration_)),
           useIntegerZoom(useIntegerZoom_) {}
 
+    CrossfadeParameters getCrossfadeParameters() const {
+        const float fraction = z - std::floor(z);
+        const std::chrono::duration<float> d = defaultFadeDuration;
+        const float t = d != std::chrono::duration<float>::zero()
+                ? std::min((now - zoomHistory.lastIntegerZoomTime) / d, 1.0f)
+                : 1.0f;
+
+        return z > zoomHistory.lastIntegerZoom
+            ? CrossfadeParameters { 2.0f, 1.0f, fraction + (1.0f - fraction) * t }
+            : CrossfadeParameters { 0.5f, 1.0f, 1 - (1 - t) * fraction };
+    }
+
     float z;
     TimePoint now;
     ZoomHistory zoomHistory;
-- 
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