[ios, macos] Convert NSColor/UIColor expressions to CSS color string values

When converting a constant NSExpression to an mbgl::Value, turn an NSColor or UIColor into an std::string containing a CSS color string. This allows developers to set an attribute of an MGLFeature to an NSColor or UIColor (rather than a CSS color string, which would be foreign), then use it in an MGLStyleFunction with identity interpolation.

1 files changed, 10 insertions, 0 deletions

diff --git a/platform/darwin/src/NSExpression+MGLAdditions.mm b/platform/darwin/src/NSExpression+MGLAdditions.mm
index c54102b8c9..a7759cda9d 100644
--- a/platform/darwin/src/NSExpression+MGLAdditions.mm
+++ b/platform/darwin/src/NSExpression+MGLAdditions.mm
@@ -1,5 +1,12 @@
 #import "NSExpression+MGLAdditions.h"
 
+#import "MGLTypes.h"
+#if TARGET_OS_IPHONE
+    #import "UIColor+MGLAdditions.h"
+#else
+    #import "NSColor+MGLAdditions.h"
+#endif
+
 @implementation NSExpression (MGLAdditions)
 
 - (std::vector<mbgl::Value>)mgl_aggregateMBGLValue {
@@ -56,6 +63,9 @@
             // We use long long here to avoid any truncation.
             return { (int64_t)number.longLongValue };
         }
+    } else if ([value isKindOfClass:[MGLColor class]]) {
+        auto hexString = [(MGLColor *)value mgl_color].stringify();
+        return { hexString };
     } else if (value && value != [NSNull null]) {
         [NSException raise:NSInvalidArgumentException
                     format:@"Can’t convert %s:%@ to mbgl::Value", [value objCType], value];