Reimplement style values atop NSExpression

include/mbgl/style/expression/interpolate.hpp

@@ -70,13 +70,20 @@ class InterpolateBase : public Expression {
     {}
 
     const std::unique_ptr<Expression>& getInput() const { return input; }
+    const Interpolator& getInterpolator() const { return interpolator; }
 
     void eachChild(const std::function<void(const Expression&)>& visit) const override {
         visit(*input);
         for (const auto& stop : stops) {
             visit(*stop.second);
         }
     }
+
+    void eachStop(const std::function<void(double, const Expression&)>& visit) const {
+        for (const auto& stop : stops) {
+            visit(stop.first, *stop.second);
+        }
+    }
 
     // Return the smallest range of stops that covers the interval [lower, upper]
     Range<float> getCoveringStops(const double lower, const double upper) const {

include/mbgl/style/expression/step.hpp

@@ -27,6 +27,7 @@ class Step : public Expression {
 
     EvaluationResult evaluate(const EvaluationContext& params) const override;
     void eachChild(const std::function<void(const Expression&)>& visit) const override;
+    void eachStop(const std::function<void(double, const Expression&)>& visit) const;
 
     const std::unique_ptr<Expression>& getInput() const { return input; }
     Range<float> getCoveringStops(const double lower, const double upper) const;

include/mbgl/style/function/camera_function.hpp

@@ -76,7 +76,9 @@ class CameraFunction {
     }
 
     bool useIntegerZoom = false;
-
+
+    const expression::Expression& getExpression() const { return *expression; }
+
     // retained for compatibility with pre-expression function API
     Stops stops;
 

include/mbgl/style/function/composite_function.hpp

@@ -111,6 +111,8 @@ class CompositeFunction {
         return *lhs.expression == *rhs.expression;
     }
 
+    const expression::Expression& getExpression() const { return *expression; }
+
     std::string property;
     Stops stops;
     optional<T> defaultValue;

include/mbgl/style/function/source_function.hpp

@@ -68,6 +68,8 @@ class SourceFunction {
 
     bool useIntegerZoom = false;
 
+    const expression::Expression& getExpression() const { return *expression; }
+
     // retained for compatibility with pre-expression function API
     std::string property;
     Stops stops;

include/mbgl/util/unitbezier.hpp

@@ -42,6 +42,17 @@ struct UnitBezier {
         , ay(1.0 - (3.0 * p1y) - (3.0 * (p2y - p1y) - (3.0 * p1y))) {
     }
 
+    std::pair<double, double> getP1() const {
+        return { cx / 3.0, cy / 3.0 };
+    }
+
+    std::pair<double, double> getP2() const {
+        return {
+            (bx + (3.0 * cx / 3.0) + cx) / 3.0,
+            (by + (3.0 * cy / 3.0) + cy) / 3.0,
+        };
+    }
+
     double sampleCurveX(double t) const {
         // `ax t^3 + bx t^2 + cx t' expanded using Horner's rule.
         return ((ax * t + bx) * t + cx) * t;

platform/darwin/docs/guides/For Style Authors.md.ejs

@@ -263,12 +263,16 @@ In style JSON | In Objective-C | In Swift
 ## Setting attribute values
 
 Each property representing a layout or paint attribute is set to an
-`MGLStyleValue` object, which is either an `MGLConstantStyleValue` object (for
-constant values) or an `MGLStyleFunction` object (for style functions). The
-style value object is a container for the raw value or function parameters that
-you want the attribute to be set to.
+`NSExpression` object. `NSExpression` objects play the same role as
+[expressions in the Mapbox Style Specification](https://www.mapbox.com/mapbox-gl-js/style-spec/#expressions),
+but you create the former using a very different syntax. `NSExpression`’s format
+string syntax is reminiscent of a spreadsheet formula or an expression in a
+database query. See the
+“[Predicates and Expressions](Predicates and Expressions.md)” guide for an
+overview of the expression support in this SDK. This SDK no longer supports
+style functions; use expressions instead.
 
-### Constant style values
+### Constant values in expressions
 
 In contrast to the JSON type that the style specification defines for each
 layout or paint property, the style value object often contains a more specific
@@ -279,10 +283,10 @@ or set.
 In style JSON | In Objective-C        | In Swift
 --------------|-----------------------|---------
 Color         | `<%- cocoaPrefix %>Color` | `<%- cocoaPrefix %>Color`
-Enum          | `NSValue` (see `NSValue(MGLAdditions)`) | `NSValue` (see `NSValue(MGLAdditions)`)
+Enum          | `NSString`            | `String`
 String        | `NSString`            | `String`
-Boolean       | `NSNumber.boolValue`  | `Bool`
-Number        | `NSNumber.floatValue` | `Float`
+Boolean       | `NSNumber.boolValue`  | `NSNumber.boolValue`
+Number        | `NSNumber.floatValue` | `NSNumber.floatValue`
 Array (`-dasharray`) | `NSArray<NSNumber>` | `[Float]`
 Array (`-font`) | `NSArray<NSString>` | `[String]`
 <% if (iOS) { -%>
@@ -312,38 +316,77 @@ translation downward. This is the reverse of how `CGVector` is interpreted on
 iOS.
 
 <% } -%>
-### Style functions
-
-A _style function_ allows you to vary the value of a layout or paint attribute
-based on the zoom level, data provided by content sources, or both. For more
-information about style functions, see “[Using Style Functions at Runtime](using-style-functions-at-runtime.html)”.
-
-Each kind of style function is represented by a distinct class, but you
-typically create style functions as you create any other style value, using
-class methods on `MGLStyleValue`:
-
-In style specification     | SDK class                   | SDK factory method
----------------------------|-----------------------------|-------------------
-zoom function              | `MGLCameraStyleFunction`    | `+[MGLStyleValue valueWithInterpolationMode:cameraStops:options:]`
-property function          | `MGLSourceStyleFunction`    | `+[MGLStyleValue valueWithInterpolationMode:sourceStops:attributeName:options:]`
-zoom-and-property function | `MGLCompositeStyleFunction` | `+[MGLStyleValue valueWithInterpolationMode:compositeStops:attributeName:options:]`
-
-The documentation for each individual style layer property indicates the kinds
-of style functions that are enabled for that property.
-
-When you create a style function, you specify an _interpolation mode_ and a
-series of _stops_. Each stop determines the effective value displayed at a
-particular zoom level (for camera functions) or the effective value on features
-with a particular attribute value in the content source (for source functions).
-The interpolation mode tells the SDK how to calculate the effective value
-between any two stops:
-
-In style specification       | In the SDK
------------------------------|-----------
-`exponential`                | `MGLInterpolationModeExponential`
-`interval`                   | `MGLInterpolationModeInterval`
-`categorical`                | `MGLInterpolationModeCategorical`
-`identity`                   | `MGLInterpolationModeIdentity`
+### Expression operators
+
+In style specification | Method, function, or predicate type | Format string syntax
+-----------------------|-------------------------------------|---------------------
+`array`                | |
+`boolean`              | |
+`literal`              | `+[NSExpression expressionForConstantValue:]` | `%@` representing `NSArray` or `NSDictionary`
+`number`               | |
+`string`               | |
+`to-boolean`           | `boolValue` |
+`to-color`             | |
+`to-number`            | `mgl_numberWithFallbackValues:` |
+`to-string`            | `stringValue` |
+`typeof`               | |
+`geometry-type`        | |
+`id`                   | |
+`properties`           | |
+`at`                   | |
+`get`                  | `+[NSExpression expressionForKeyPath:]` | Key path
+`has`                  | |
+`length`               | `count:` | `count({1, 2, 2, 3, 4, 7, 9})`
+`!`                    | `NSNotPredicateType` | `NOT (p0 OR … OR pn)`
+`!=`                   | `NSNotEqualToPredicateOperatorType` | `key != value`
+`<`                    | `NSLessThanPredicateOperatorType` | `key < value`
+`<=`                   | `NSLessThanOrEqualToPredicateOperatorType` | `key <= value`
+`==`                   | `NSEqualToPredicateOperatorType` | `key == value`
+`>`                    | `NSGreaterThanPredicateOperatorType` | `key > value`
+`>=`                   | `NSGreaterThanOrEqualToPredicateOperatorType` | `key >= value`
+`all`                  | `NSAndPredicateType` | `p0 AND … AND pn`
+`any`                  | `NSOrPredicateType` | `p0 OR … OR pn`
+`case`                 | `+[NSExpression expressionForConditional:trueExpression:falseExpression:]` | `TERNARY(condition, trueExpression, falseExpression)`
+`coalesce`             | |
+`match`                | |
+`interpolate`          | `mgl_interpolateWithCurveType:parameters:stops:` |
+`step`                 | `mgl_stepWithMinimum:stops:` |
+`let`                  | `mgl_expressionWithContext:` |
+`var`                  | `+[NSExpression expressionForVariable:]` | `$variable`
+`concat`               | `stringByAppendingString:` |
+`downcase`             | `lowercase:` | `lowercase('DOWNTOWN')`
+`upcase`               | `uppercase:` | `uppercase('Elysian Fields')`
+<% if (macOS) { -%>
+`rgb`                  | `+[NSColor colorWithCalibratedRed:green:blue:alpha:]` |
+`rgba`                 | `+[NSColor colorWithCalibratedRed:green:blue:alpha:]` |
+<% } else { %>
+`rgb`                  | `+[UIColor colorWithRed:green:blue:alpha:]` |
+`rgba`                 | `+[UIColor colorWithRed:green:blue:alpha:]` |
+<% } -%>
+`to-rgba`              | |
+`-`                    | `from:subtract:` | `2 - 1`
+`*`                    | `multiply:by:` | `1 * 2`
+`/`                    | `divide:by:` | `1 / 2`
+`%`                    | `modulus:by:` |
+`^`                    | `raise:toPower:` | `2 ** 2`
+`+`                    | `add:to:` | `1 + 2`
+`acos`                 | |
+`asin`                 | |
+`atan`                 | |
+`cos`                  | |
+`e`                    | | `%@` representing `NSNumber` containing `M_E`
+`ln`                   | `ln:` | `ln(2)`
+`ln2`                  | | `%@` representing `NSNumber` containing `M_LN2`
+`log10`                | `log:` | `log(1)`
+`log2`                 | |
+`max`                  | `max:` | `max({1, 2, 2, 3, 4, 7, 9})`
+`min`                  | `min:` | `min({1, 2, 2, 3, 4, 7, 9})`
+`pi`                   | | `%@` representing `NSNumber` containing `M_PI`
+`sin`                  | |
+`sqrt`                 | `sqrt:` | `sqrt(2)`
+`tan`                  | |
+`zoom`                 | | `$zoom`
+`heatmap-density`      | | `$heatmapDensity`
 
 ## Filtering sources
 
@@ -368,5 +411,5 @@ In style JSON             | In the format string
 `["any", f0, …, fn]`      | `p0 OR … OR pn`
 `["none", f0, …, fn]`     | `NOT (p0 OR … OR pn)`
 
-See the `MGLVectorStyleLayer.predicate` documentation for a full description of
-the supported operators and operand types.
+See the “[Predicates and Expressions](Predicates and Expressions.md)” guide for
+a full description of the supported operators and operand types.