Made sure not to turn on wide gamut support without impeller. (flutter#41460)

fixes flutter#125430

[C++, Objective-C, Java style guides]: https://github.com/flutter/engine/blob/main/CONTRIBUTING.md#style

Author: gaaclarke

shell/platform/darwin/ios/framework/Source/FlutterDartProject.mm

@@ -439,4 +439,8 @@ - (BOOL)isWideGamutEnabled {
   return _settings.enable_wide_gamut;
 }
 
+- (BOOL)isImpellerEnabled {
+  return _settings.enable_impeller;
+}
+
 @end

shell/platform/darwin/ios/framework/Source/FlutterDartProject_Internal.h

@@ -20,6 +20,7 @@ flutter::Settings FLTDefaultSettingsForBundle(NSBundle* _Nullable bundle = nil,
 @interface FlutterDartProject ()
 
 @property(nonatomic, readonly) BOOL isWideGamutEnabled;
+@property(nonatomic, readonly) BOOL isImpellerEnabled;
 
 /**
  * This is currently used for *only for tests* to override settings.

shell/platform/darwin/ios/framework/Source/FlutterEngine.mm

@@ -1402,6 +1402,10 @@ - (FlutterDartProject*)project {
   return _dartProject.get();
 }
 
+- (BOOL)isUsingImpeller {
+  return self.project.isImpellerEnabled;
+}
+
 @end
 
 @implementation FlutterEngineRegistrar {

shell/platform/darwin/ios/framework/Source/FlutterView.h

@@ -17,6 +17,8 @@
 
 @protocol FlutterViewEngineDelegate <NSObject>
 
+@property(nonatomic, readonly) BOOL isUsingImpeller;
+
 - (flutter::Rasterizer::Screenshot)takeScreenshot:(flutter::Rasterizer::ScreenshotType)type
                                   asBase64Encoded:(BOOL)base64Encode;
 

shell/platform/darwin/ios/framework/Source/FlutterView.mm

@@ -16,19 +16,6 @@
 #import "flutter/shell/platform/darwin/ios/ios_surface_software.h"
 #include "third_party/skia/include/utils/mac/SkCGUtils.h"
 
-static BOOL IsWideGamutSupported() {
-#if TARGET_OS_SIMULATOR
-  // As of Xcode 14.1, the wide gamut surface pixel formats are not supported by
-  // the simulator.
-  return NO;
-#else
-  // This predicates the decision on the capabilities of the iOS device's
-  // display.  This means external displays will not support wide gamut if the
-  // device's display doesn't support it.  It practice that should be never.
-  return UIScreen.mainScreen.traitCollection.displayGamut != UIDisplayGamutSRGB;
-#endif
-}
-
 @implementation FlutterView {
   id<FlutterViewEngineDelegate> _delegate;
   BOOL _isWideGamutEnabled;
@@ -49,6 +36,30 @@ - (instancetype)initWithCoder:(NSCoder*)aDecoder {
   return nil;
 }
 
+- (UIScreen*)screen {
+  if (@available(iOS 13.0, *)) {
+    return self.window.windowScene.screen;
+  }
+  return UIScreen.mainScreen;
+}
+
+- (BOOL)isWideGamutSupported {
+#if TARGET_OS_SIMULATOR
+  // As of Xcode 14.1, the wide gamut surface pixel formats are not supported by
+  // the simulator.
+  return NO;
+#endif
+
+  if (![_delegate isUsingImpeller]) {
+    return NO;
+  }
+
+  // This predicates the decision on the capabilities of the iOS device's
+  // display.  This means external displays will not support wide gamut if the
+  // device's display doesn't support it.  It practice that should be never.
+  return self.screen.traitCollection.displayGamut != UIDisplayGamutSRGB;
+}
+
 - (instancetype)initWithDelegate:(id<FlutterViewEngineDelegate>)delegate
                           opaque:(BOOL)opaque
                  enableWideGamut:(BOOL)isWideGamutEnabled {
@@ -63,7 +74,7 @@ - (instancetype)initWithDelegate:(id<FlutterViewEngineDelegate>)delegate
   if (self) {
     _delegate = delegate;
     _isWideGamutEnabled = isWideGamutEnabled;
-    if (_isWideGamutEnabled && !IsWideGamutSupported()) {
+    if (_isWideGamutEnabled && self.isWideGamutSupported) {
       FML_DLOG(WARNING) << "Rendering wide gamut colors is turned on but isn't "
                            "supported, downgrading the color gamut to sRGB.";
     }
@@ -92,7 +103,7 @@ - (void)layoutSubviews {
     layer.contentsScale = screenScale;
     layer.rasterizationScale = screenScale;
     layer.framebufferOnly = flutter::Settings::kSurfaceDataAccessible ? NO : YES;
-    if (_isWideGamutEnabled && IsWideGamutSupported()) {
+    if (_isWideGamutEnabled && self.isWideGamutSupported) {
       CGColorSpaceRef srgb = CGColorSpaceCreateWithName(kCGColorSpaceExtendedSRGB);
       layer.colorspace = srgb;
       CFRelease(srgb);

shell/platform/darwin/ios/framework/Source/FlutterViewTest.mm

@@ -9,6 +9,7 @@
 
 @interface FakeDelegate : NSObject <FlutterViewEngineDelegate>
 @property(nonatomic) BOOL callbackCalled;
+@property(nonatomic, assign) BOOL isUsingImpeller;
 @end
 
 @implementation FakeDelegate {
@@ -55,4 +56,14 @@ - (void)testFlutterViewBackgroundColorIsNotNil {
   XCTAssertNotNil(view.backgroundColor);
 }
 
+- (void)testIgnoreWideColorWithoutImpeller {
+  FakeDelegate* delegate = [[FakeDelegate alloc] init];
+  delegate.isUsingImpeller = NO;
+  FlutterView* view = [[FlutterView alloc] initWithDelegate:delegate opaque:NO enableWideGamut:YES];
+  [view layoutSubviews];
+  XCTAssertTrue([view.layer isKindOfClass:NSClassFromString(@"CAMetalLayer")]);
+  CAMetalLayer* layer = (CAMetalLayer*)view.layer;
+  XCTAssertEqual(layer.pixelFormat, MTLPixelFormatBGRA8Unorm);
+}
+
 @end