[core] Add `line-gradient` property

Porting of https://github.com/mapbox/mapbox-gl-js/pull/6303
See the link above for the description of the feature and
its limitations).

Based on patch from @lbud (Lauren Budorick).

1 files changed, 17 insertions, 0 deletions

diff --git a/platform/darwin/src/MGLLineStyleLayer.mm b/platform/darwin/src/MGLLineStyleLayer.mm
index 3bad2a8b98..5cf0762475 100644
--- a/platform/darwin/src/MGLLineStyleLayer.mm
+++ b/platform/darwin/src/MGLLineStyleLayer.mm
@@ -306,6 +306,23 @@ namespace mbgl {
     return transition;
 }
 
+- (void)setLineGradient:(NSExpression *)lineGradient {
+    MGLAssertStyleLayerIsValid();
+
+    auto mbglValue = MGLStyleValueTransformer<mbgl::Color, MGLColor *>().toPropertyValue<mbgl::style::ColorRampPropertyValue>(lineGradient);
+    self.rawLayer->setLineGradient(mbglValue);
+}
+
+- (NSExpression *)lineGradient {
+    MGLAssertStyleLayerIsValid();
+
+    auto propertyValue = self.rawLayer->getLineGradient();
+    if (propertyValue.isUndefined()) {
+        propertyValue = self.rawLayer->getDefaultLineGradient();
+    }
+    return MGLStyleValueTransformer<mbgl::Color, MGLColor *>().toExpression(propertyValue);
+}
+
 - (void)setLineOffset:(NSExpression *)lineOffset {
     MGLAssertStyleLayerIsValid();