[darwin] Generate style code for symbol-sort-key

3 files changed, 116 insertions, 2 deletions

diff --git a/platform/darwin/src/MGLSymbolStyleLayer.h b/platform/darwin/src/MGLSymbolStyleLayer.h
index 5c12b28544..f5047745f6 100644
--- a/platform/darwin/src/MGLSymbolStyleLayer.h
+++ b/platform/darwin/src/MGLSymbolStyleLayer.h
@@ -158,6 +158,11 @@ typedef NS_ENUM(NSUInteger, MGLSymbolPlacement) {
  */
 typedef NS_ENUM(NSUInteger, MGLSymbolZOrder) {
     /**
+     If `MGLSymbolStyleLayer.symbolSortKey` is set, sort based on that.
+     Otherwise sort symbols by their position relative to the viewport.
+     */
+    MGLSymbolZOrderAuto,
+    /**
      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.
@@ -1019,6 +1024,23 @@ MGL_EXPORT
 @property (nonatomic, null_resettable) NSExpression *symbolPlacement;
 
 /**
+ Sorts features in ascending order based on this value. Features with a higher
+ sort key will appear above features with a lower sort key wehn they overlap.
+ Features with a lower sort key will have priority over other features when
+ doing placement.
+ 
+ You can set this property to an expression containing any of the following:
+ 
+ * Constant numeric values
+ * Predefined functions, including mathematical and string operators
+ * Conditional expressions
+ * Variable assignments and references to assigned variables
+ * Interpolation and step functions applied to the `$zoomLevel` variable and/or
+ feature attributes
+ */
+@property (nonatomic, null_resettable) NSExpression *symbolSortKey;
+
+/**
  Distance between two symbol anchors.
  
  This property is measured in points.
@@ -1045,13 +1067,15 @@ MGL_EXPORT
 /**
  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.
+ The default value of this property is an expression that evaluates to `auto`.
+ 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:
+   * `auto`: If `symbol-sort-key` is set, sort based on that. Otherwise sort
+ symbols by their position relative to the viewport.
    * `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.
diff --git a/platform/darwin/src/MGLSymbolStyleLayer.mm b/platform/darwin/src/MGLSymbolStyleLayer.mm
index 6d91bbe87f..e54a0b9a15 100644
--- a/platform/darwin/src/MGLSymbolStyleLayer.mm
+++ b/platform/darwin/src/MGLSymbolStyleLayer.mm
@@ -54,6 +54,7 @@ namespace mbgl {
     });
 
     MBGL_DEFINE_ENUM(MGLSymbolZOrder, {
+        { MGLSymbolZOrderAuto, "auto" },
         { MGLSymbolZOrderViewportY, "viewport-y" },
         { MGLSymbolZOrderSource, "source" },
     });
@@ -587,6 +588,24 @@ namespace mbgl {
     return MGLStyleValueTransformer<mbgl::style::SymbolPlacementType, NSValue *, mbgl::style::SymbolPlacementType, MGLSymbolPlacement>().toExpression(propertyValue);
 }
 
+- (void)setSymbolSortKey:(NSExpression *)symbolSortKey {
+    MGLAssertStyleLayerIsValid();
+    MGLLogDebug(@"Setting symbolSortKey: %@", symbolSortKey);
+
+    auto mbglValue = MGLStyleValueTransformer<float, NSNumber *>().toPropertyValue<mbgl::style::PropertyValue<float>>(symbolSortKey, true);
+    self.rawLayer->setSymbolSortKey(mbglValue);
+}
+
+- (NSExpression *)symbolSortKey {
+    MGLAssertStyleLayerIsValid();
+
+    auto propertyValue = self.rawLayer->getSymbolSortKey();
+    if (propertyValue.isUndefined()) {
+        propertyValue = self.rawLayer->getDefaultSymbolSortKey();
+    }
+    return MGLStyleValueTransformer<float, NSNumber *>().toExpression(propertyValue);
+}
+
 - (void)setSymbolSpacing:(NSExpression *)symbolSpacing {
     MGLAssertStyleLayerIsValid();
     MGLLogDebug(@"Setting symbolSpacing: %@", symbolSpacing);
diff --git a/platform/darwin/test/MGLSymbolStyleLayerTests.mm b/platform/darwin/test/MGLSymbolStyleLayerTests.mm
index 083b12bcc3..87091acc1b 100644
--- a/platform/darwin/test/MGLSymbolStyleLayerTests.mm
+++ b/platform/darwin/test/MGLSymbolStyleLayerTests.mm
@@ -1003,6 +1003,75 @@
         XCTAssertThrowsSpecificNamed(layer.symbolPlacement = functionExpression, NSException, NSInvalidArgumentException, @"MGLSymbolLayer should raise an exception if a camera-data expression is applied to a property that does not support key paths to feature attributes.");
     }
 
+    // symbol-sort-key
+    {
+        XCTAssertTrue(rawLayer->getSymbolSortKey().isUndefined(),
+                      @"symbol-sort-key should be unset initially.");
+        NSExpression *defaultExpression = layer.symbolSortKey;
+
+        NSExpression *constantExpression = [NSExpression expressionWithFormat:@"1"];
+        layer.symbolSortKey = constantExpression;
+        mbgl::style::PropertyValue<float> propertyValue = { 1.0 };
+        XCTAssertEqual(rawLayer->getSymbolSortKey(), propertyValue,
+                       @"Setting symbolSortKey to a constant value expression should update symbol-sort-key.");
+        XCTAssertEqualObjects(layer.symbolSortKey, constantExpression,
+                              @"symbolSortKey should round-trip constant value expressions.");
+
+        constantExpression = [NSExpression expressionWithFormat:@"1"];
+        NSExpression *functionExpression = [NSExpression expressionWithFormat:@"mgl_step:from:stops:($zoomLevel, %@, %@)", constantExpression, @{@18: constantExpression}];
+        layer.symbolSortKey = functionExpression;
+
+        {
+            using namespace mbgl::style::expression::dsl;
+            propertyValue = mbgl::style::PropertyExpression<float>(
+                step(zoom(), literal(1.0), 18.0, literal(1.0))
+            );
+        }
+
+        XCTAssertEqual(rawLayer->getSymbolSortKey(), propertyValue,
+                       @"Setting symbolSortKey to a camera expression should update symbol-sort-key.");
+        XCTAssertEqualObjects(layer.symbolSortKey, functionExpression,
+                              @"symbolSortKey should round-trip camera expressions.");
+
+        functionExpression = [NSExpression expressionWithFormat:@"mgl_interpolate:withCurveType:parameters:stops:(keyName, 'linear', nil, %@)", @{@18: constantExpression}];
+        layer.symbolSortKey = functionExpression;
+
+        {
+            using namespace mbgl::style::expression::dsl;
+            propertyValue = mbgl::style::PropertyExpression<float>(
+                interpolate(linear(), number(get("keyName")), 18.0, literal(1.0))
+            );
+        }
+
+        XCTAssertEqual(rawLayer->getSymbolSortKey(), propertyValue,
+                       @"Setting symbolSortKey to a data expression should update symbol-sort-key.");
+        NSExpression *pedanticFunctionExpression = [NSExpression expressionWithFormat:@"mgl_interpolate:withCurveType:parameters:stops:(CAST(keyName, 'NSNumber'), 'linear', nil, %@)", @{@18: constantExpression}];
+        XCTAssertEqualObjects(layer.symbolSortKey, pedanticFunctionExpression,
+                              @"symbolSortKey should round-trip data expressions.");
+
+        functionExpression = [NSExpression expressionWithFormat:@"mgl_interpolate:withCurveType:parameters:stops:($zoomLevel, 'linear', nil, %@)", @{@10: functionExpression}];
+        layer.symbolSortKey = functionExpression;
+
+        {
+            using namespace mbgl::style::expression::dsl;
+            propertyValue = mbgl::style::PropertyExpression<float>(
+                interpolate(linear(), zoom(), 10.0, interpolate(linear(), number(get("keyName")), 18.0, literal(1.0)))
+            );
+        }
+
+        XCTAssertEqual(rawLayer->getSymbolSortKey(), propertyValue,
+                       @"Setting symbolSortKey to a camera-data expression should update symbol-sort-key.");
+        pedanticFunctionExpression = [NSExpression expressionWithFormat:@"mgl_interpolate:withCurveType:parameters:stops:($zoomLevel, 'linear', nil, %@)", @{@10: pedanticFunctionExpression}];
+        XCTAssertEqualObjects(layer.symbolSortKey, pedanticFunctionExpression,
+                              @"symbolSortKey should round-trip camera-data expressions.");
+
+        layer.symbolSortKey = nil;
+        XCTAssertTrue(rawLayer->getSymbolSortKey().isUndefined(),
+                      @"Unsetting symbolSortKey should return symbol-sort-key to the default value.");
+        XCTAssertEqualObjects(layer.symbolSortKey, defaultExpression,
+                              @"symbolSortKey should return the default value after being unset.");
+    }
+
     // symbol-spacing
     {
         XCTAssertTrue(rawLayer->getSymbolSpacing().isUndefined(),
@@ -2994,6 +3063,7 @@
     [self testPropertyName:@"maximum-text-width" isBoolean:NO];
     [self testPropertyName:@"symbol-avoids-edges" isBoolean:YES];
     [self testPropertyName:@"symbol-placement" isBoolean:NO];
+    [self testPropertyName:@"symbol-sort-key" isBoolean:NO];
     [self testPropertyName:@"symbol-spacing" isBoolean:NO];
     [self testPropertyName:@"symbol-z-order" isBoolean:NO];
     [self testPropertyName:@"text" isBoolean:NO];
@@ -3053,6 +3123,7 @@
     XCTAssertEqual([NSValue valueWithMGLSymbolPlacement:MGLSymbolPlacementPoint].MGLSymbolPlacementValue, MGLSymbolPlacementPoint);
     XCTAssertEqual([NSValue valueWithMGLSymbolPlacement:MGLSymbolPlacementLine].MGLSymbolPlacementValue, MGLSymbolPlacementLine);
     XCTAssertEqual([NSValue valueWithMGLSymbolPlacement:MGLSymbolPlacementLineCenter].MGLSymbolPlacementValue, MGLSymbolPlacementLineCenter);
+    XCTAssertEqual([NSValue valueWithMGLSymbolZOrder:MGLSymbolZOrderAuto].MGLSymbolZOrderValue, MGLSymbolZOrderAuto);
     XCTAssertEqual([NSValue valueWithMGLSymbolZOrder:MGLSymbolZOrderViewportY].MGLSymbolZOrderValue, MGLSymbolZOrderViewportY);
     XCTAssertEqual([NSValue valueWithMGLSymbolZOrder:MGLSymbolZOrderSource].MGLSymbolZOrderValue, MGLSymbolZOrderSource);
     XCTAssertEqual([NSValue valueWithMGLTextAnchor:MGLTextAnchorCenter].MGLTextAnchorValue, MGLTextAnchorCenter);