6 files changed, 445 insertions, 6 deletions
diff --git a/platform/darwin/src/MGLHeatmapStyleLayer.h b/platform/darwin/src/MGLHeatmapStyleLayer.h
new file mode 100644
index 0000000000..35095fd52e
--- /dev/null
+++ b/platform/darwin/src/MGLHeatmapStyleLayer.h
@@ -0,0 +1,189 @@
+// This file is generated.
+// Edit platform/darwin/scripts/generate-style-code.js, then run `make darwin-style-code`.
+
+#import "MGLFoundation.h"
+#import "MGLVectorStyleLayer.h"
+
+NS_ASSUME_NONNULL_BEGIN
+
+/**
+ An `MGLHeatmapStyleLayer` is a style layer that renders a <a
+ href="https://en.wikipedia.org/wiki/Heat_map">heatmap</a>.
+ 
+ A heatmap visualizes the spatial distribution of a large, dense set of point
+ data, using color to avoid cluttering the map with individual points at low
+ zoom levels. The points are weighted by an attribute you specify. Use a heatmap
+ style layer in conjunction with point or point collection features in vector
+ tiles loaded by an `MGLVectorSource` object or `MGLPointAnnotation`,
+ `MGLPointFeature`, `MGLPointCollection`, or `MGLPointCollectionFeature`
+ instances in an `MGLShapeSource` object.
+ 
+ Consider accompanying a heatmap style layer with an `MGLCircleStyleLayer` or
+ `MGLSymbolStyleLayer` at high zoom levels. If you are unsure whether the point
+ data in an `MGLShapeSource` is dense enough to warrant a heatmap, you can
+ alternatively cluster the source using the `MGLShapeSourceOptionClustered`
+ option and render the data using an `MGLCircleStyleLayer` or
+ `MGLSymbolStyleLayer`.
+
+ You can access an existing heatmap style layer using the
+ `-[MGLStyle layerWithIdentifier:]` method if you know its identifier;
+ otherwise, find it using the `MGLStyle.layers` property. You can also create a
+ new heatmap style layer and add it to the style using a method such as
+ `-[MGLStyle addLayer:]`.
+
+ ### Example
+
+ ```swift
+ let layer = MGLHeatmapStyleLayer(identifier: "earthquake-heat", source: earthquakes)
+ layer.heatmapWeight = NSExpression(format: "FUNCTION(magnitude, 'mgl_interpolateWithCurveType:parameters:stops:', 'linear', nil, %@)",
+                                    [0: 0,
+                                     6: 1])
+ layer.heatmapIntensity = NSExpression(format: "FUNCTION($zoomLevel, 'mgl_interpolateWithCurveType:parameters:stops:', 'linear', nil, %@)",
+                                       [0: 1,
+                                        9: 3])
+ mapView.style?.addLayer(layer)
+ ```
+ */
+MGL_EXPORT
+@interface MGLHeatmapStyleLayer : MGLVectorStyleLayer
+
+/**
+ Returns a heatmap style layer initialized with an identifier and source.
+
+ After initializing and configuring the style layer, add it to a map view’s
+ style using the `-[MGLStyle addLayer:]` or
+ `-[MGLStyle insertLayer:belowLayer:]` method.
+
+ @param identifier A string that uniquely identifies the source in the style to
+    which it is added.
+ @param source The source from which to obtain the data to style. If the source
+    has not yet been added to the current style, the behavior is undefined.
+ @return An initialized foreground style layer.
+ */
+- (instancetype)initWithIdentifier:(NSString *)identifier source:(MGLSource *)source;
+
+#pragma mark - Accessing the Paint Attributes
+
+/**
+ Defines the color of each point based on its density value in a heatmap. Should
+ be an expression that uses `$heatmapDensity` as input.
+ 
+ The default value of this property is an expression that evaluates to a rainbow
+ color scale from blue to red. 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 `UIColor` values
+ * Predefined functions, including mathematical and string operators
+ * Conditional expressions
+ * Variable assignments and references to assigned variables
+ * Interpolation and step functions applied to the `$heatmapDensity` variable
+ 
+ This property does not support applying interpolation or step functions to
+ feature attributes.
+ */
+@property (nonatomic, null_resettable) NSExpression *heatmapColor;
+
+/**
+ Similar to `heatmapWeight` but controls the intensity of the heatmap globally.
+ Primarily used for adjusting the heatmap based on zoom level.
+ 
+ The default value of this property is an expression that evaluates to the float
+ `1`. Set this property to `nil` to reset it to the default value.
+ 
+ You can set this property to an expression containing any of the following:
+ 
+ * Constant numeric values
+ * Predefined functions, including mathematical and string operators
+ * Conditional expressions
+ * Variable assignments and references to assigned variables
+ * Interpolation and step functions applied to the `$zoomLevel` variable
+ 
+ This property does not support applying interpolation or step functions to
+ feature attributes.
+ */
+@property (nonatomic, null_resettable) NSExpression *heatmapIntensity;
+
+/**
+ The transition affecting any changes to this layer’s `heatmapIntensity` property.
+
+ This property corresponds to the `heatmap-intensity-transition` property in the style JSON file format.
+*/
+@property (nonatomic) MGLTransition heatmapIntensityTransition;
+
+/**
+ The global opacity at which the heatmap layer will be drawn.
+ 
+ The default value of this property is an expression that evaluates to the float
+ `1`. 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 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 `$zoomLevel` variable
+ 
+ This property does not support applying interpolation or step functions to
+ feature attributes.
+ */
+@property (nonatomic, null_resettable) NSExpression *heatmapOpacity;
+
+/**
+ The transition affecting any changes to this layer’s `heatmapOpacity` property.
+
+ This property corresponds to the `heatmap-opacity-transition` property in the style JSON file format.
+*/
+@property (nonatomic) MGLTransition heatmapOpacityTransition;
+
+/**
+ Radius of influence of one heatmap point in points. Increasing the value makes
+ the heatmap smoother, but less detailed.
+ 
+ This property is measured in points.
+ 
+ The default value of this property is an expression that evaluates to the float
+ `30`. Set this property to `nil` to reset it to the default value.
+ 
+ You can set this property to an expression containing any of the following:
+ 
+ * Constant numeric values
+ * Predefined functions, including mathematical and string operators
+ * Conditional expressions
+ * Variable assignments and references to assigned variables
+ * Interpolation and step functions applied to the `$zoomLevel` variable and/or
+ feature attributes
+ */
+@property (nonatomic, null_resettable) NSExpression *heatmapRadius;
+
+/**
+ The transition affecting any changes to this layer’s `heatmapRadius` property.
+
+ This property corresponds to the `heatmap-radius-transition` property in the style JSON file format.
+*/
+@property (nonatomic) MGLTransition heatmapRadiusTransition;
+
+/**
+ A measure of how much an individual point contributes to the heatmap. A value
+ of 10 would be equivalent to having 10 points of weight 1 in the same spot.
+ Especially useful when combined with clustering.
+ 
+ The default value of this property is an expression that evaluates to the float
+ `1`. 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 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 *heatmapWeight;
+
+@end
+
+NS_ASSUME_NONNULL_END
diff --git a/platform/darwin/src/MGLHeatmapStyleLayer.mm b/platform/darwin/src/MGLHeatmapStyleLayer.mm
new file mode 100644
index 0000000000..a394dbda3b
--- /dev/null
+++ b/platform/darwin/src/MGLHeatmapStyleLayer.mm
@@ -0,0 +1,210 @@
+// This file is generated.
+// Edit platform/darwin/scripts/generate-style-code.js, then run `make darwin-style-code`.
+
+#import "MGLSource.h"
+#import "NSPredicate+MGLAdditions.h"
+#import "NSDate+MGLAdditions.h"
+#import "MGLStyleLayer_Private.h"
+#import "MGLStyleValue_Private.h"
+#import "MGLHeatmapStyleLayer.h"
+
+#include <mbgl/style/transition_options.hpp>
+#include <mbgl/style/layers/heatmap_layer.hpp>
+
+@interface MGLHeatmapStyleLayer ()
+
+@property (nonatomic, readonly) mbgl::style::HeatmapLayer *rawLayer;
+
+@end
+
+@implementation MGLHeatmapStyleLayer
+
+- (instancetype)initWithIdentifier:(NSString *)identifier source:(MGLSource *)source
+{
+    auto layer = std::make_unique<mbgl::style::HeatmapLayer>(identifier.UTF8String, source.identifier.UTF8String);
+    return self = [super initWithPendingLayer:std::move(layer)];
+}
+
+- (mbgl::style::HeatmapLayer *)rawLayer
+{
+    return (mbgl::style::HeatmapLayer *)super.rawLayer;
+}
+
+- (NSString *)sourceIdentifier
+{
+    MGLAssertStyleLayerIsValid();
+
+    return @(self.rawLayer->getSourceID().c_str());
+}
+
+- (NSString *)sourceLayerIdentifier
+{
+    MGLAssertStyleLayerIsValid();
+
+    auto layerID = self.rawLayer->getSourceLayer();
+    return layerID.empty() ? nil : @(layerID.c_str());
+}
+
+- (void)setSourceLayerIdentifier:(NSString *)sourceLayerIdentifier
+{
+    MGLAssertStyleLayerIsValid();
+
+    self.rawLayer->setSourceLayer(sourceLayerIdentifier.UTF8String ?: "");
+}
+
+- (void)setPredicate:(NSPredicate *)predicate
+{
+    MGLAssertStyleLayerIsValid();
+
+    self.rawLayer->setFilter(predicate ? predicate.mgl_filter : mbgl::style::NullFilter());
+}
+
+- (NSPredicate *)predicate
+{
+    MGLAssertStyleLayerIsValid();
+
+    return [NSPredicate mgl_predicateWithFilter:self.rawLayer->getFilter()];
+}
+
+#pragma mark - Accessing the Paint Attributes
+
+- (void)setHeatmapColor:(NSExpression *)heatmapColor {
+    MGLAssertStyleLayerIsValid();
+
+    auto mbglValue = MGLStyleValueTransformer<mbgl::Color, MGLColor *>().toPropertyValue<mbgl::style::HeatmapColorPropertyValue>(heatmapColor);
+    self.rawLayer->setHeatmapColor(mbglValue);
+}
+
+- (NSExpression *)heatmapColor {
+    MGLAssertStyleLayerIsValid();
+
+    auto propertyValue = self.rawLayer->getHeatmapColor();
+    if (propertyValue.isUndefined()) {
+        propertyValue = self.rawLayer->getDefaultHeatmapColor();
+    }
+    return MGLStyleValueTransformer<mbgl::Color, MGLColor *>().toExpression(propertyValue);
+}
+
+- (void)setHeatmapIntensity:(NSExpression *)heatmapIntensity {
+    MGLAssertStyleLayerIsValid();
+
+    auto mbglValue = MGLStyleValueTransformer<float, NSNumber *>().toPropertyValue<mbgl::style::PropertyValue<float>>(heatmapIntensity);
+    self.rawLayer->setHeatmapIntensity(mbglValue);
+}
+
+- (NSExpression *)heatmapIntensity {
+    MGLAssertStyleLayerIsValid();
+
+    auto propertyValue = self.rawLayer->getHeatmapIntensity();
+    if (propertyValue.isUndefined()) {
+        propertyValue = self.rawLayer->getDefaultHeatmapIntensity();
+    }
+    return MGLStyleValueTransformer<float, NSNumber *>().toExpression(propertyValue);
+}
+
+- (void)setHeatmapIntensityTransition:(MGLTransition )transition {
+    MGLAssertStyleLayerIsValid();
+
+    mbgl::style::TransitionOptions options { { MGLDurationFromTimeInterval(transition.duration) }, { MGLDurationFromTimeInterval(transition.delay) } };
+    self.rawLayer->setHeatmapIntensityTransition(options);
+}
+
+- (MGLTransition)heatmapIntensityTransition {
+    MGLAssertStyleLayerIsValid();
+
+    mbgl::style::TransitionOptions transitionOptions = self.rawLayer->getHeatmapIntensityTransition();
+    MGLTransition transition;
+    transition.duration = MGLTimeIntervalFromDuration(transitionOptions.duration.value_or(mbgl::Duration::zero()));
+    transition.delay = MGLTimeIntervalFromDuration(transitionOptions.delay.value_or(mbgl::Duration::zero()));
+
+    return transition;
+}
+
+- (void)setHeatmapOpacity:(NSExpression *)heatmapOpacity {
+    MGLAssertStyleLayerIsValid();
+
+    auto mbglValue = MGLStyleValueTransformer<float, NSNumber *>().toPropertyValue<mbgl::style::PropertyValue<float>>(heatmapOpacity);
+    self.rawLayer->setHeatmapOpacity(mbglValue);
+}
+
+- (NSExpression *)heatmapOpacity {
+    MGLAssertStyleLayerIsValid();
+
+    auto propertyValue = self.rawLayer->getHeatmapOpacity();
+    if (propertyValue.isUndefined()) {
+        propertyValue = self.rawLayer->getDefaultHeatmapOpacity();
+    }
+    return MGLStyleValueTransformer<float, NSNumber *>().toExpression(propertyValue);
+}
+
+- (void)setHeatmapOpacityTransition:(MGLTransition )transition {
+    MGLAssertStyleLayerIsValid();
+
+    mbgl::style::TransitionOptions options { { MGLDurationFromTimeInterval(transition.duration) }, { MGLDurationFromTimeInterval(transition.delay) } };
+    self.rawLayer->setHeatmapOpacityTransition(options);
+}
+
+- (MGLTransition)heatmapOpacityTransition {
+    MGLAssertStyleLayerIsValid();
+
+    mbgl::style::TransitionOptions transitionOptions = self.rawLayer->getHeatmapOpacityTransition();
+    MGLTransition transition;
+    transition.duration = MGLTimeIntervalFromDuration(transitionOptions.duration.value_or(mbgl::Duration::zero()));
+    transition.delay = MGLTimeIntervalFromDuration(transitionOptions.delay.value_or(mbgl::Duration::zero()));
+
+    return transition;
+}
+
+- (void)setHeatmapRadius:(NSExpression *)heatmapRadius {
+    MGLAssertStyleLayerIsValid();
+
+    auto mbglValue = MGLStyleValueTransformer<float, NSNumber *>().toPropertyValue<mbgl::style::DataDrivenPropertyValue<float>>(heatmapRadius);
+    self.rawLayer->setHeatmapRadius(mbglValue);
+}
+
+- (NSExpression *)heatmapRadius {
+    MGLAssertStyleLayerIsValid();
+
+    auto propertyValue = self.rawLayer->getHeatmapRadius();
+    if (propertyValue.isUndefined()) {
+        propertyValue = self.rawLayer->getDefaultHeatmapRadius();
+    }
+    return MGLStyleValueTransformer<float, NSNumber *>().toExpression(propertyValue);
+}
+
+- (void)setHeatmapRadiusTransition:(MGLTransition )transition {
+    MGLAssertStyleLayerIsValid();
+
+    mbgl::style::TransitionOptions options { { MGLDurationFromTimeInterval(transition.duration) }, { MGLDurationFromTimeInterval(transition.delay) } };
+    self.rawLayer->setHeatmapRadiusTransition(options);
+}
+
+- (MGLTransition)heatmapRadiusTransition {
+    MGLAssertStyleLayerIsValid();
+
+    mbgl::style::TransitionOptions transitionOptions = self.rawLayer->getHeatmapRadiusTransition();
+    MGLTransition transition;
+    transition.duration = MGLTimeIntervalFromDuration(transitionOptions.duration.value_or(mbgl::Duration::zero()));
+    transition.delay = MGLTimeIntervalFromDuration(transitionOptions.delay.value_or(mbgl::Duration::zero()));
+
+    return transition;
+}
+
+- (void)setHeatmapWeight:(NSExpression *)heatmapWeight {
+    MGLAssertStyleLayerIsValid();
+
+    auto mbglValue = MGLStyleValueTransformer<float, NSNumber *>().toPropertyValue<mbgl::style::DataDrivenPropertyValue<float>>(heatmapWeight);
+    self.rawLayer->setHeatmapWeight(mbglValue);
+}
+
+- (NSExpression *)heatmapWeight {
+    MGLAssertStyleLayerIsValid();
+
+    auto propertyValue = self.rawLayer->getHeatmapWeight();
+    if (propertyValue.isUndefined()) {
+        propertyValue = self.rawLayer->getDefaultHeatmapWeight();
+    }
+    return MGLStyleValueTransformer<float, NSNumber *>().toExpression(propertyValue);
+}
+
+@end
diff --git a/platform/darwin/src/MGLStyle.mm b/platform/darwin/src/MGLStyle.mm
index 5128944312..f6fc5533be 100644
--- a/platform/darwin/src/MGLStyle.mm
+++ b/platform/darwin/src/MGLStyle.mm
@@ -8,6 +8,7 @@
 #import "MGLLineStyleLayer.h"
 #import "MGLCircleStyleLayer.h"
 #import "MGLSymbolStyleLayer.h"
+#import "MGLHeatmapStyleLayer.h"
 #import "MGLHillshadeStyleLayer.h"
 #import "MGLRasterStyleLayer.h"
 #import "MGLBackgroundStyleLayer.h"
@@ -36,6 +37,7 @@
 #include <mbgl/style/layers/line_layer.hpp>
 #include <mbgl/style/layers/symbol_layer.hpp>
 #include <mbgl/style/layers/raster_layer.hpp>
+#include <mbgl/style/layers/heatmap_layer.hpp>
 #include <mbgl/style/layers/hillshade_layer.hpp>
 #include <mbgl/style/layers/circle_layer.hpp>
 #include <mbgl/style/layers/background_layer.hpp>
@@ -401,6 +403,8 @@ static NSURL *MGLStyleURL_trafficNight;
         return [[MGLSymbolStyleLayer alloc] initWithRawLayer:symbolLayer];
     } else if (auto rasterLayer = rawLayer->as<mbgl::style::RasterLayer>()) {
         return [[MGLRasterStyleLayer alloc] initWithRawLayer:rasterLayer];
+    } else if (auto heatmapLayer = rawLayer->as<mbgl::style::HeatmapLayer>()) {
+        return [[MGLHeatmapStyleLayer alloc] initWithRawLayer:heatmapLayer];
     } else if (auto hillshadeLayer = rawLayer->as<mbgl::style::HillshadeLayer>()) {
         return [[MGLHillshadeStyleLayer alloc] initWithRawLayer:hillshadeLayer];
     } else if (auto circleLayer = rawLayer->as<mbgl::style::CircleLayer>()) {
diff --git a/platform/darwin/src/MGLStyleLayer.mm.ejs b/platform/darwin/src/MGLStyleLayer.mm.ejs
index 41b029791f..ac7676a1cc 100644
--- a/platform/darwin/src/MGLStyleLayer.mm.ejs
+++ b/platform/darwin/src/MGLStyleLayer.mm.ejs
@@ -157,7 +157,9 @@ namespace mbgl {
 - (void)set<%- camelize(property.name) %>:(NSExpression *)<%- objCName(property) %> {
     MGLAssertStyleLayerIsValid();
 
-<% if (property["property-function"]) { -%>
+<% if (property.name === 'heatmap-color') { -%>
+    auto mbglValue = MGLStyleValueTransformer<mbgl::Color, MGLColor *>().toPropertyValue<mbgl::style::HeatmapColorPropertyValue>(heatmapColor);
+<% } else if (property["property-function"]) { -%>
     auto mbglValue = MGLStyleValueTransformer<<%- valueTransformerArguments(property).join(', ') %>>().toPropertyValue<mbgl::style::DataDrivenPropertyValue<<%- valueTransformerArguments(property)[0] %>>>(<%- objCName(property) %>);
 <% } else { -%>
     auto mbglValue = MGLStyleValueTransformer<<%- valueTransformerArguments(property).join(', ') %>>().toPropertyValue<mbgl::style::PropertyValue<<%- valueTransformerArguments(property)[0] %>>>(<%- objCName(property) %>);
diff --git a/platform/darwin/src/MGLStyleValue_Private.h b/platform/darwin/src/MGLStyleValue_Private.h
index ba4b413a3c..5124c29a90 100644
--- a/platform/darwin/src/MGLStyleValue_Private.h
+++ b/platform/darwin/src/MGLStyleValue_Private.h
@@ -10,6 +10,7 @@
 #import "MGLConversion.h"
 #include <mbgl/style/conversion/property_value.hpp>
 #include <mbgl/style/conversion/data_driven_property_value.hpp>
+#include <mbgl/style/conversion/heatmap_color_property_value.hpp>
 #include <mbgl/style/conversion/position.hpp>
 #import <mbgl/style/types.hpp>
 
@@ -52,11 +53,20 @@ public:
         return mbglValue.evaluate(evaluator);
     }
     
+    // Convert an mbgl heatmap color property value into an mgl style value
+    NSExpression *toExpression(const mbgl::style::HeatmapColorPropertyValue &mbglValue) {
+        if (mbglValue.isUndefined()) {
+            return nil;
+        }
+        return [NSExpression mgl_expressionWithJSONObject:MGLJSONObjectFromMBGLExpression(mbglValue.getExpression())];
+    }
+
     /**
      Converts an NSExpression to an mbgl property value.
      */
     template <typename MBGLValue>
-    MBGLValue toPropertyValue(NSExpression *expression) {
+    typename std::enable_if_t<!std::is_same<MBGLValue, mbgl::style::HeatmapColorPropertyValue>::value,
+    MBGLValue> toPropertyValue(NSExpression *expression) {
         if (!expression) {
             return {};
         }
@@ -85,6 +95,30 @@ public:
         
         return *value;
     }
+    
+    /**
+     Converts an NSExpression to an mbgl property value.
+     */
+    template <typename MBGLValue>
+    typename std::enable_if_t<std::is_same<MBGLValue, mbgl::style::HeatmapColorPropertyValue>::value,
+    MBGLValue> toPropertyValue(NSExpression *expression) {
+        if (!expression) {
+            return {};
+        }
+        
+        NSArray *jsonExpression = expression.mgl_jsonExpressionObject;
+        
+        mbgl::style::conversion::Error valueError;
+        auto value = mbgl::style::conversion::convert<mbgl::style::HeatmapColorPropertyValue>(
+            mbgl::style::conversion::makeConvertible(jsonExpression), valueError);
+        if (!value) {
+            [NSException raise:NSInvalidArgumentException
+                        format:@"Invalid property value: %@", @(valueError.message.c_str())];
+            return {};
+        }
+        
+        return *value;
+    }
 
 private: // Private utilities for converting from mgl to mbgl values
     
diff --git a/platform/darwin/src/MGLVectorStyleLayer.h b/platform/darwin/src/MGLVectorStyleLayer.h
index 7780a34c7f..177b1b70f0 100644
--- a/platform/darwin/src/MGLVectorStyleLayer.h
+++ b/platform/darwin/src/MGLVectorStyleLayer.h
@@ -10,10 +10,10 @@ NS_ASSUME_NONNULL_BEGIN
  is defined by an `MGLShapeSource` or `MGLVectorSource` object.
 
  Create instances of `MGLCircleStyleLayer`, `MGLFillStyleLayer`,
- `MGLFillExtrusionStyleLayer`, `MGLLineStyleLayer`, and `MGLSymbolStyleLayer` in
- order to use `MGLVectorStyleLayer`'s properties and methods. Do not create
- instances of `MGLVectorStyleLayer` directly, and do not create your own
- subclasses of this class.
+ `MGLFillExtrusionStyleLayer`, `MGLHeatmapStyleLayer`, `MGLLineStyleLayer`, and
+ `MGLSymbolStyleLayer` in order to use `MGLVectorStyleLayer`'s properties and
+ methods. Do not create instances of `MGLVectorStyleLayer` directly, and do not
+ create your own subclasses of this class.
  */
 MGL_EXPORT
 @interface MGLVectorStyleLayer : MGLForegroundStyleLayer