2 files changed, 91 insertions, 0 deletions

diff --git a/platform/darwin/src/MGLSymbolStyleLayer.h b/platform/darwin/src/MGLSymbolStyleLayer.h
index afaea9a74f..363f9efee7 100644
--- a/platform/darwin/src/MGLSymbolStyleLayer.h
+++ b/platform/darwin/src/MGLSymbolStyleLayer.h
@@ -151,6 +151,26 @@ typedef NS_ENUM(NSUInteger, MGLSymbolPlacement) {
 };
 
 /**
+ Controls the order in which overlapping symbols in the same layer are rendered
+
+ Values of this type are used in the `MGLSymbolStyleLayer.symbolZOrder`
+ property.
+ */
+typedef NS_ENUM(NSUInteger, MGLSymbolZOrder) {
+    /**
+     Specify this z order if symbols’ appearance relies on lower features
+     overlapping higher features. For example, symbols with a pin-like
+     appearance would require this z order.
+     */
+    MGLSymbolZOrderViewportY,
+    /**
+     Specify this z order if the order in which features appear in the source is
+     significant.
+     */
+    MGLSymbolZOrderSource,
+};
+
+/**
  Part of the text placed closest to the anchor.
 
  Values of this type are used in the `MGLSymbolStyleLayer.textAnchor`
@@ -1005,6 +1025,32 @@ MGL_EXPORT
 @property (nonatomic, null_resettable) NSExpression *symbolSpacing;
 
 /**
+ Controls the order in which overlapping symbols in the same layer are rendered
+ 
+ The default value of this property is an expression that evaluates to
+ `viewport-y`. Set this property to `nil` to reset it to the default value.
+ 
+ You can set this property to an expression containing any of the following:
+ 
+ * Constant `MGLSymbolZOrder` values
+ * Any of the following constant string values:
+   * `viewport-y`: Specify this z order if symbols’ appearance relies on lower
+ features overlapping higher features. For example, symbols with a pin-like
+ appearance would require this z order.
+   * `source`: Specify this z order if the order in which features appear in the
+ source is significant.
+ * Predefined functions, including mathematical and string operators
+ * Conditional expressions
+ * Variable assignments and references to assigned variables
+ * Step functions applied to the `$zoomLevel` variable
+ 
+ This property does not support applying interpolation functions to the
+ `$zoomLevel` variable or applying interpolation or step functions to feature
+ attributes.
+ */
+@property (nonatomic, null_resettable) NSExpression *symbolZOrder;
+
+/**
  Value to use for a text label.
  
  Within a constant string value, a feature attribute name enclosed in curly
@@ -2141,6 +2187,19 @@ MGL_EXPORT
 @property (readonly) MGLSymbolPlacement MGLSymbolPlacementValue;
 
 /**
+ Creates a new value object containing the given `MGLSymbolZOrder` enumeration.
+
+ @param symbolZOrder The value for the new object.
+ @return A new value object that contains the enumeration value.
+ */
++ (instancetype)valueWithMGLSymbolZOrder:(MGLSymbolZOrder)symbolZOrder;
+
+/**
+ The `MGLSymbolZOrder` enumeration representation of the value.
+ */
+@property (readonly) MGLSymbolZOrder MGLSymbolZOrderValue;
+
+/**
  Creates a new value object containing the given `MGLTextAnchor` enumeration.
 
  @param textAnchor The value for the new object.
diff --git a/platform/darwin/src/MGLSymbolStyleLayer.mm b/platform/darwin/src/MGLSymbolStyleLayer.mm
index ad023a1a03..4c0fcfe539 100644
--- a/platform/darwin/src/MGLSymbolStyleLayer.mm
+++ b/platform/darwin/src/MGLSymbolStyleLayer.mm
@@ -50,6 +50,11 @@ namespace mbgl {
         { MGLSymbolPlacementLineCenter, "line-center" },
     });
 
+    MBGL_DEFINE_ENUM(MGLSymbolZOrder, {
+        { MGLSymbolZOrderViewportY, "viewport-y" },
+        { MGLSymbolZOrderSource, "source" },
+    });
+
     MBGL_DEFINE_ENUM(MGLTextAnchor, {
         { MGLTextAnchorCenter, "center" },
         { MGLTextAnchorLeft, "left" },
@@ -573,6 +578,23 @@ namespace mbgl {
     return MGLStyleValueTransformer<float, NSNumber *>().toExpression(propertyValue);
 }
 
+- (void)setSymbolZOrder:(NSExpression *)symbolZOrder {
+    MGLAssertStyleLayerIsValid();
+
+    auto mbglValue = MGLStyleValueTransformer<mbgl::style::SymbolZOrderType, NSValue *, mbgl::style::SymbolZOrderType, MGLSymbolZOrder>().toPropertyValue<mbgl::style::PropertyValue<mbgl::style::SymbolZOrderType>>(symbolZOrder, false);
+    self.rawLayer->setSymbolZOrder(mbglValue);
+}
+
+- (NSExpression *)symbolZOrder {
+    MGLAssertStyleLayerIsValid();
+
+    auto propertyValue = self.rawLayer->getSymbolZOrder();
+    if (propertyValue.isUndefined()) {
+        propertyValue = self.rawLayer->getDefaultSymbolZOrder();
+    }
+    return MGLStyleValueTransformer<mbgl::style::SymbolZOrderType, NSValue *, mbgl::style::SymbolZOrderType, MGLSymbolZOrder>().toExpression(propertyValue);
+}
+
 - (void)setText:(NSExpression *)text {
     MGLAssertStyleLayerIsValid();
 
@@ -1440,6 +1462,16 @@ namespace mbgl {
     return symbolPlacement;
 }
 
++ (NSValue *)valueWithMGLSymbolZOrder:(MGLSymbolZOrder)symbolZOrder {
+    return [NSValue value:&symbolZOrder withObjCType:@encode(MGLSymbolZOrder)];
+}
+
+- (MGLSymbolZOrder)MGLSymbolZOrderValue {
+    MGLSymbolZOrder symbolZOrder;
+    [self getValue:&symbolZOrder];
+    return symbolZOrder;
+}
+
 + (NSValue *)valueWithMGLTextAnchor:(MGLTextAnchor)textAnchor {
     return [NSValue value:&textAnchor withObjCType:@encode(MGLTextAnchor)];
 }