[ios, macos] Add text-color support to format expressions. (#14146)

Added the possibility of overriding paint properties inside the format expression.

Added an example of how to create an MGLAttributedExpression object and documented the attributes keys and value types.

Fixed a bug that ignored the font names.

3 files changed, 15 insertions, 3 deletions

diff --git a/platform/macos/docs/guides/For Style Authors.md b/platform/macos/docs/guides/For Style Authors.md
index 038ddf1f93..220ce3d50e 100644
--- a/platform/macos/docs/guides/For Style Authors.md
+++ b/platform/macos/docs/guides/For Style Authors.md
@@ -411,5 +411,16 @@ In style JSON             | In the format string
 `["any", f0, …, fn]`      | `p0 OR … OR pn`
 `["none", f0, …, fn]`     | `NOT (p0 OR … OR pn)`
 
+## Specifying the text format
+
+The following format attributes are defined as `NSString` constans that you
+can use to update the formatting of `MGLSymbolStyleLayer.text` property.
+
+In style JSON | In Objective-C        | In Swift
+--------------|-----------------------|---------
+`text-font`      | `MGLFontNamesAttribute` | `.fontNamesAttribute`
+`font-scale`      | `MGLFontSizeAttribute` | `.fontSizeAttribute`
+`text-color`  | `MGLFontColorAttribute` | `.fontColorAttribute`
+
 See the “[Predicates and Expressions](predicates-and-expressions.html)” guide for
 a full description of the supported operators and operand types.
diff --git a/platform/macos/src/NSColor+MGLAdditions.h b/platform/macos/src/NSColor+MGLAdditions.h
index 21c939fec6..a3c5aba63f 100644
--- a/platform/macos/src/NSColor+MGLAdditions.h
+++ b/platform/macos/src/NSColor+MGLAdditions.h
@@ -23,5 +23,6 @@
 
 + (NSExpression *)mgl_expressionForRGBComponents:(NSArray<NSExpression *> *)components;
 + (NSExpression *)mgl_expressionForRGBAComponents:(NSArray<NSExpression *> *)components;
++ (NSColor *)mgl_colorWithRGBComponents:(NSArray<NSExpression *> *)componentExpressions;
 
 @end
diff --git a/platform/macos/src/NSColor+MGLAdditions.mm b/platform/macos/src/NSColor+MGLAdditions.mm
index c73c1a41b7..ea7d99f66d 100644
--- a/platform/macos/src/NSColor+MGLAdditions.mm
+++ b/platform/macos/src/NSColor+MGLAdditions.mm
@@ -37,7 +37,7 @@
 @implementation NSExpression (MGLColorAdditions)
 
 + (NSExpression *)mgl_expressionForRGBComponents:(NSArray<NSExpression *> *)components {
-    if (NSColor *color = [self mgl_colorWithComponentExpressions:components]) {
+    if (NSColor *color = [self mgl_colorWithRGBComponents:components]) {
         return [NSExpression expressionForConstantValue:color];
     }
     
@@ -49,7 +49,7 @@
 }
 
 + (NSExpression *)mgl_expressionForRGBAComponents:(NSArray<NSExpression *> *)components {
-    if (NSColor *color = [self mgl_colorWithComponentExpressions:components]) {
+    if (NSColor *color = [self mgl_colorWithRGBComponents:components]) {
         return [NSExpression expressionForConstantValue:color];
     }
     
@@ -62,7 +62,7 @@
 /**
  Returns a color object corresponding to the given component expressions.
  */
-+ (NSColor *)mgl_colorWithComponentExpressions:(NSArray<NSExpression *> *)componentExpressions {
++ (NSColor *)mgl_colorWithRGBComponents:(NSArray<NSExpression *> *)componentExpressions {
     // Map the component expressions to constant components. If any component is
     // a non-constant expression, the components cannot be converted into a
     // constant color value.