[ios, macos] More robust color conversion

3 files changed, 85 insertions, 14 deletions

diff --git a/platform/darwin/src/NSExpression+MGLAdditions.mm b/platform/darwin/src/NSExpression+MGLAdditions.mm
index 8108ddb7b9..2bdebc89bb 100644
--- a/platform/darwin/src/NSExpression+MGLAdditions.mm
+++ b/platform/darwin/src/NSExpression+MGLAdditions.mm
@@ -901,16 +901,9 @@ NSArray *MGLSubexpressionsWithJSONObjects(NSArray *objects) {
                             format:@"Casting expression to %@ not yet implemented.", type];
             } else if ([function isEqualToString:@"MGL_FUNCTION"]) {
                 return self.arguments.mgl_jsonExpressionObject;
-            } else if (op == [MGLColor class]) {
-                if ([function isEqualToString:@"colorWithRed:green:blue:"]
-                    || [function isEqualToString:@"colorWithCalibratedRed:green:blue:"]) {
-                    NSArray *arguments = self.arguments.mgl_jsonExpressionObject;
-                    return [@[@"rgb"] arrayByAddingObjectsFromArray:arguments];
-                } else if ([function isEqualToString:@"colorWithRed:green:blue:alpha:"]
-                           || [function isEqualToString:@"colorWithCalibratedRed:green:blue:alpha:"]) {
-                    NSArray *arguments = self.arguments.mgl_jsonExpressionObject;
-                    return [@[@"rgba"] arrayByAddingObjectsFromArray:arguments];
-                }
+            } else if (op == [MGLColor class] && [function isEqualToString:@"colorWithRed:green:blue:alpha:"]) {
+                NSArray *arguments = self.arguments.mgl_jsonExpressionObject;
+                return [@[@"rgba"] arrayByAddingObjectsFromArray:arguments];
             } else if ([function isEqualToString:@"median:"] ||
                        [function isEqualToString:@"mode:"] ||
                        [function isEqualToString:@"stddev:"] ||
diff --git a/platform/ios/src/UIColor+MGLAdditions.mm b/platform/ios/src/UIColor+MGLAdditions.mm
index 2b8dfb0446..9ca39acda4 100644
--- a/platform/ios/src/UIColor+MGLAdditions.mm
+++ b/platform/ios/src/UIColor+MGLAdditions.mm
@@ -25,13 +25,48 @@
 @implementation NSExpression (MGLColorAdditions)
 
 + (NSExpression *)mgl_expressionForRGBComponents:(NSArray<NSExpression *> *)components {
+    if (UIColor *color = [self mgl_colorWithRGBComponents:components]) {
+        return [NSExpression expressionForConstantValue:color];
+    }
+    
     NSExpression *color = [NSExpression expressionForConstantValue:[UIColor class]];
-    return [NSExpression expressionForFunction:color selectorName:@"colorWithRed:green:blue:" arguments:components];
+    NSExpression *alpha = [NSExpression expressionForConstantValue:@1.0];
+    return [NSExpression expressionForFunction:color
+                                  selectorName:@"colorWithRed:green:blue:alpha:"
+                                     arguments:[components arrayByAddingObject:alpha]];
 }
 
 + (NSExpression *)mgl_expressionForRGBAComponents:(NSArray<NSExpression *> *)components {
+    if (UIColor *color = [self mgl_colorWithRGBComponents:components]) {
+        return [NSExpression expressionForConstantValue:color];
+    }
+    
     NSExpression *color = [NSExpression expressionForConstantValue:[UIColor class]];
-    return [NSExpression expressionForFunction:color selectorName:@"colorWithRed:green:blue:alpha:" arguments:components];
+    return [NSExpression expressionForFunction:color
+                                  selectorName:@"colorWithRed:green:blue:alpha:"
+                                     arguments:components];
+}
+
++ (UIColor *)mgl_colorWithRGBComponents:(NSArray<NSExpression *> *)components {
+    if (components.count < 3 || components.count > 4) {
+        return nil;
+    }
+    
+    for (NSExpression *component in components) {
+        if (component.expressionType != NSConstantValueExpressionType) {
+            return nil;
+        }
+        
+        NSNumber *number = (NSNumber *)component.constantValue;
+        if (![number isKindOfClass:[NSNumber class]]) {
+            return nil;
+        }
+    }
+    
+    return [UIColor colorWithRed:[components[0].constantValue doubleValue] / 255.0
+                           green:[components[1].constantValue doubleValue] / 255.0
+                            blue:[components[2].constantValue doubleValue] / 255.0
+                           alpha:components.count == 3 ? [components[3].constantValue doubleValue] : 1.0];
 }
 
 @end
diff --git a/platform/macos/src/NSColor+MGLAdditions.mm b/platform/macos/src/NSColor+MGLAdditions.mm
index e80a2910f8..4ffc1ef0b2 100644
--- a/platform/macos/src/NSColor+MGLAdditions.mm
+++ b/platform/macos/src/NSColor+MGLAdditions.mm
@@ -37,13 +37,56 @@
 @implementation NSExpression (MGLColorAdditions)
 
 + (NSExpression *)mgl_expressionForRGBComponents:(NSArray<NSExpression *> *)components {
+    if (NSColor *color = [self mgl_colorWithComponentExpressions:components]) {
+        return [NSExpression expressionForConstantValue:color];
+    }
+    
     NSExpression *color = [NSExpression expressionForConstantValue:[NSColor class]];
-    return [NSExpression expressionForFunction:color selectorName:@"colorWithCalibratedRed:green:blue:" arguments:components];
+    NSExpression *alpha = [NSExpression expressionForConstantValue:@1.0];
+    return [NSExpression expressionForFunction:color
+                                  selectorName:@"colorWithRed:green:blue:alpha:"
+                                     arguments:[components arrayByAddingObject:alpha]];
 }
 
 + (NSExpression *)mgl_expressionForRGBAComponents:(NSArray<NSExpression *> *)components {
+    if (NSColor *color = [self mgl_colorWithComponentExpressions:components]) {
+        return [NSExpression expressionForConstantValue:color];
+    }
+    
     NSExpression *color = [NSExpression expressionForConstantValue:[NSColor class]];
-    return [NSExpression expressionForFunction:color selectorName:@"colorWithCalibratedRed:green:blue:alpha:" arguments:components];
+    return [NSExpression expressionForFunction:color
+                                  selectorName:@"colorWithRed:green:blue:alpha:"
+                                     arguments:components];
+}
+
+/**
+ Returns a color object corresponding to the given component expressions.
+ */
++ (NSColor *)mgl_colorWithComponentExpressions:(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.
+    std::vector<CGFloat> components;
+    for (NSExpression *componentExpression in componentExpressions) {
+        if (componentExpression.expressionType != NSConstantValueExpressionType) {
+            return nil;
+        }
+        
+        NSNumber *component = (NSNumber *)componentExpression.constantValue;
+        if (![component isKindOfClass:[NSNumber class]]) {
+            return nil;
+        }
+        
+        components.push_back(component.doubleValue / 255.0);
+    }
+    // Alpha
+    components.back() *= 255.0;
+    
+    // The Mapbox Style Specification does not specify a color space, but it is
+    // assumed to be sRGB for consistency with CSS.
+    return [NSColor colorWithColorSpace:[NSColorSpace sRGBColorSpace]
+                             components:&components[0]
+                                  count:components.size()];
 }
 
 @end