[core] Variable label placement

platform/darwin/scripts/generate-style-code.js

@@ -137,6 +137,8 @@ global.objCTestValue = function (property, layerType, arraysAsStructs, indent) {
                     }
                     return '@"{1, 1}"';
                 }
+                case 'anchor':
+                    return `@"{'top','bottom'}"`;
                 default:
                     throw new Error(`unknown array type for ${property.name}`);
             }
@@ -185,6 +187,8 @@ global.mbglTestValue = function (property, layerType) {
                 case 'offset':
                 case 'translate':
                     return '{ 1, 1 }';
+                case 'anchor':
+                    return '{ mbgl::style::SymbolAnchorType::Top, mbgl::style::SymbolAnchorType::Bottom }';
                 default:
                     throw new Error(`unknown array type for ${property.name}`);
             }
@@ -200,6 +204,13 @@ global.mbglExpressionTestValue = function (property, layerType) {
             return `"${_.last(_.keys(property.values))}"`;
         case 'color':
             return 'mbgl::Color(1, 0, 0, 1)';
+        case 'array':
+            switch (arrayType(property)) {
+                case 'anchor':
+                    return `{"top", "bottom"}`;
+                default:
+                    break;
+            }
         default:
             return global.mbglTestValue(property, layerType);
     }
@@ -539,11 +550,12 @@ global.propertyType = function (property) {
                 case 'font':
                     return 'NSArray<NSString *> *';
                 case 'padding':
-                    return 'NSValue *';
                 case 'position':
                 case 'offset':
                 case 'translate':
                     return 'NSValue *';
+                case 'anchor':
+                    return 'NSArray<NSValue *> *';
                 default:
                     throw new Error(`unknown array type for ${property.name}`);
             }
@@ -588,6 +600,8 @@ global.valueTransformerArguments = function (property) {
                 case 'offset':
                 case 'translate':
                     return ['std::array<float, 2>', objCType];
+                case 'anchor':
+                    return ['std::vector<mbgl::style::SymbolAnchorType>', objCType, 'mbgl::style::SymbolAnchorType', 'MGLTextAnchor'];
                 default:
                     throw new Error(`unknown array type for ${property.name}`);
             }
@@ -637,6 +651,8 @@ global.mbglType = function(property) {
                     return 'std::array<float, 2>';
                 case 'position':
                     return 'mbgl::style::Position';
+                case 'anchor':
+                    return 'std::vector<mbgl::style::SymbolAnchorType>';
                 default:
                     throw new Error(`unknown array type for ${property.name}`);
             }

platform/darwin/src/MGLStyleValue_Private.h

@@ -307,10 +307,8 @@ class MGLStyleValueTransformer {
 
     // Enumerations
     template <typename MBGLEnum = MBGLType, typename MGLEnum = ObjCEnum>
-    static NSValue *toMGLRawStyleValue(const MBGLEnum &value) {
-        auto str = mbgl::Enum<MBGLEnum>::toString(value);
-        MGLEnum mglType = *mbgl::Enum<MGLEnum>::toEnum(str);
-        return [NSValue value:&mglType withObjCType:@encode(MGLEnum)];
+    static NSString *toMGLRawStyleValue(const MBGLEnum &value) {
+        return @(mbgl::Enum<MBGLEnum>::toString(value));
     }
 
     /// Converts all types of mbgl property values into an equivalent NSExpression.
@@ -320,15 +318,6 @@ class MGLStyleValueTransformer {
             return nil;
         }
 
-        /**
-         As hack to allow converting enum => string values, we accept a second, dummy parameter in
-         the toRawStyleSpecValue() methods for converting 'atomic' (non-style-function) values.
-         This allows us to use `std::enable_if` to test (at compile time) whether or not MBGLType is an Enum.
-         */
-        template <typename MBGLEnum = MBGLType,
-            class = typename std::enable_if<!std::is_enum<MBGLEnum>::value>::type,
-        typename MGLEnum = ObjCEnum,
-            class = typename std::enable_if<!std::is_enum<MGLEnum>::value>::type>
         NSExpression *operator()(const MBGLType &value) const {
             id constantValue = toMGLRawStyleValue(value);
             if ([constantValue isKindOfClass:[NSArray class]]) {
@@ -337,15 +326,6 @@ class MGLStyleValueTransformer {
             return [NSExpression expressionForConstantValue:constantValue];
         }
 
-        template <typename MBGLEnum = MBGLType,
-            class = typename std::enable_if<std::is_enum<MBGLEnum>::value>::type,
-        typename MGLEnum = ObjCEnum,
-            class = typename std::enable_if<std::is_enum<MGLEnum>::value>::type>
-        NSExpression *operator()(const MBGLEnum &value) const {
-            NSString *constantValue = @(mbgl::Enum<MBGLEnum>::toString(value));
-            return [NSExpression expressionForConstantValue:constantValue];
-        }
-
         NSExpression *operator()(const mbgl::style::PropertyExpression<MBGLType> &mbglValue) const {
             return [NSExpression expressionWithMGLJSONObject:MGLJSONObjectFromMBGLExpression(mbglValue.getExpression())];
         }

platform/darwin/src/MGLSymbolStyleLayer.h

@@ -222,6 +222,10 @@ typedef NS_ENUM(NSUInteger, MGLTextAnchor) {
  property.
  */
 typedef NS_ENUM(NSUInteger, MGLTextJustification) {
+    /**
+     The text is aligned towards the anchor position.
+     */
+    MGLTextJustificationAuto,
     /**
      The text is aligned to the left.
      */
@@ -1279,6 +1283,7 @@ MGL_EXPORT
 
  * Constant `MGLTextJustification` values
  * Any of the following constant string values:
+   * `auto`: The text is aligned towards the anchor position.
    * `left`: The text is aligned to the left.
    * `center`: The text is centered.
    * `right`: The text is aligned to the right.
@@ -1349,8 +1354,8 @@ MGL_EXPORT
  `NSValue` object containing a `CGVector` struct set to 0 ems rightward and 0
  ems downward. Set this property to `nil` to reset it to the default value.
 
- This property is only applied to the style if `text` is non-`nil`. Otherwise,
- it is ignored.
+ This property is only applied to the style if `text` is non-`nil`, and
+ `textRadialOffset` is set to `nil`. Otherwise, it is ignored.
 
  You can set this property to an expression containing any of the following:
 
@@ -1372,8 +1377,8 @@ MGL_EXPORT
  `NSValue` object containing a `CGVector` struct set to 0 ems rightward and 0
  ems upward. Set this property to `nil` to reset it to the default value.
 
- This property is only applied to the style if `text` is non-`nil`. Otherwise,
- it is ignored.
+ This property is only applied to the style if `text` is non-`nil`, and
+ `textRadialOffset` is set to `nil`. Otherwise, it is ignored.
 
  You can set this property to an expression containing any of the following:
 
@@ -1463,6 +1468,27 @@ MGL_EXPORT
  */
 @property (nonatomic, null_resettable) NSExpression *textPitchAlignment;
 
+/**
+ Radial offset of text, in the direction of the symbol's anchor. Useful in
+ combination with `textVariableAnchor`, which doesn't support the
+ two-dimensional `textOffset`.
+
+ This property is measured in ems.
+
+ This property is only applied to the style if `textOffset` is set to `nil`.
+ Otherwise, it is ignored.
+
+ 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 *textRadialOffset;
+
 /**
  Rotates the text clockwise.
 
@@ -1549,6 +1575,32 @@ MGL_EXPORT
  */
 @property (nonatomic, null_resettable) NSExpression *textTransform;
 
+/**
+ To increase the chance of placing high-priority labels on the map, you can
+ provide an array of `textAnchor` locations: the render will attempt to place
+ the label at each location, in order, before moving onto the next label. Use
+ `textJustify: auto` to choose justification based on anchor position. To apply
+ an offset, use the `textRadialOffset` instead of the two-dimensional
+ `textOffset`.
+
+ This property is only applied to the style if `textAnchor` is set to `nil`, and
+ `textOffset` is set to `nil`, and `symbolPlacement` is set to an expression
+ that evaluates to or `MGLSymbolPlacementPoint`. Otherwise, it is ignored.
+
+ You can set this property to an expression containing any of the following:
+
+ * Constant array values
+ * 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 *textVariableAnchor;
+
 #pragma mark - Accessing the Paint Attributes
 
 #if TARGET_OS_IPHONE

platform/darwin/src/MGLSymbolStyleLayer.mm

@@ -71,6 +71,7 @@
     });
 
     MBGL_DEFINE_ENUM(MGLTextJustification, {
+        { MGLTextJustificationAuto, "auto" },
         { MGLTextJustificationLeft, "left" },
         { MGLTextJustificationCenter, "center" },
         { MGLTextJustificationRight, "right" },
@@ -906,6 +907,24 @@ - (NSExpression *)textPitchAlignment {
     return MGLStyleValueTransformer<mbgl::style::AlignmentType, NSValue *, mbgl::style::AlignmentType, MGLTextPitchAlignment>().toExpression(propertyValue);
 }
 
+- (void)setTextRadialOffset:(NSExpression *)textRadialOffset {
+    MGLAssertStyleLayerIsValid();
+    MGLLogDebug(@"Setting textRadialOffset: %@", textRadialOffset);
+
+    auto mbglValue = MGLStyleValueTransformer<float, NSNumber *>().toPropertyValue<mbgl::style::PropertyValue<float>>(textRadialOffset, true);
+    self.rawLayer->setTextRadialOffset(mbglValue);
+}
+
+- (NSExpression *)textRadialOffset {
+    MGLAssertStyleLayerIsValid();
+
+    auto propertyValue = self.rawLayer->getTextRadialOffset();
+    if (propertyValue.isUndefined()) {
+        propertyValue = self.rawLayer->getDefaultTextRadialOffset();
+    }
+    return MGLStyleValueTransformer<float, NSNumber *>().toExpression(propertyValue);
+}
+
 - (void)setTextRotation:(NSExpression *)textRotation {
     MGLAssertStyleLayerIsValid();
     MGLLogDebug(@"Setting textRotation: %@", textRotation);
@@ -967,6 +986,24 @@ - (NSExpression *)textTransform {
     return MGLStyleValueTransformer<mbgl::style::TextTransformType, NSValue *, mbgl::style::TextTransformType, MGLTextTransform>().toExpression(propertyValue);
 }
 
+- (void)setTextVariableAnchor:(NSExpression *)textVariableAnchor {
+    MGLAssertStyleLayerIsValid();
+    MGLLogDebug(@"Setting textVariableAnchor: %@", textVariableAnchor);
+
+    auto mbglValue = MGLStyleValueTransformer<std::vector<mbgl::style::SymbolAnchorType>, NSArray<NSValue *> *, mbgl::style::SymbolAnchorType, MGLTextAnchor>().toPropertyValue<mbgl::style::PropertyValue<std::vector<mbgl::style::SymbolAnchorType>>>(textVariableAnchor, false);
+    self.rawLayer->setTextVariableAnchor(mbglValue);
+}
+
+- (NSExpression *)textVariableAnchor {
+    MGLAssertStyleLayerIsValid();
+
+    auto propertyValue = self.rawLayer->getTextVariableAnchor();
+    if (propertyValue.isUndefined()) {
+        propertyValue = self.rawLayer->getDefaultTextVariableAnchor();
+    }
+    return MGLStyleValueTransformer<std::vector<mbgl::style::SymbolAnchorType>, NSArray<NSValue *> *, mbgl::style::SymbolAnchorType, MGLTextAnchor>().toExpression(propertyValue);
+}
+
 #pragma mark - Accessing the Paint Attributes
 
 - (void)setIconColor:(NSExpression *)iconColor {