PlatformView Blur for Backdrop Filter

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

@@ -384,6 +384,7 @@ - (BOOL)flt_hasFirstResponderInViewHierarchySubtree {
   if (flutter_view_ == nullptr) {
     return;
   }
+
   FML_DCHECK(CATransform3DEqualToTransform(embedded_view.layer.transform, CATransform3DIdentity));
   ResetAnchor(embedded_view.layer);
   ChildClippingView* clipView = (ChildClippingView*)embedded_view.superview;
@@ -423,6 +424,7 @@ - (BOOL)flt_hasFirstResponderInViewHierarchySubtree {
         embedded_view.alpha = (*iter)->GetAlphaFloat() * embedded_view.alpha;
         break;
       case kBackdropFilter:
+        [clipView applyBackdropFilterWithRadius:@(5)];
         break;
     }
     ++iter;

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

@@ -3,6 +3,7 @@
 // found in the LICENSE file.
 
 #import <OCMock/OCMock.h>
+#import <UIKit/UIKit.h>
 #import <XCTest/XCTest.h>
 
 #import "flutter/shell/platform/darwin/common/framework/Headers/FlutterBinaryMessenger.h"
@@ -242,6 +243,129 @@ - (void)testChildClippingViewHitTests {
   XCTAssertTrue([childClippingView pointInside:CGPointMake(199, 199) withEvent:nil]);
 }
 
+- (void)testChildClippingViewApplyBackdropFilter {
+  flutter::FlutterPlatformViewsTestMockPlatformViewDelegate mock_delegate;
+  auto thread_task_runner = CreateNewThread("FlutterPlatformViewsTest");
+  flutter::TaskRunners runners(/*label=*/self.name.UTF8String,
+                               /*platform=*/thread_task_runner,
+                               /*raster=*/thread_task_runner,
+                               /*ui=*/thread_task_runner,
+                               /*io=*/thread_task_runner);
+  auto flutterPlatformViewsController = std::make_shared<flutter::FlutterPlatformViewsController>();
+  auto platform_view = std::make_unique<flutter::PlatformViewIOS>(
+      /*delegate=*/mock_delegate,
+      /*rendering_api=*/flutter::IOSRenderingAPI::kSoftware,
+      /*platform_views_controller=*/flutterPlatformViewsController,
+      /*task_runners=*/runners);
+
+  FlutterPlatformViewsTestMockFlutterPlatformFactory* factory =
+      [[FlutterPlatformViewsTestMockFlutterPlatformFactory new] autorelease];
+  flutterPlatformViewsController->RegisterViewFactory(
+      factory, @"MockFlutterPlatformView",
+      FlutterPlatformViewGestureRecognizersBlockingPolicyEager);
+  FlutterResult result = ^(id result) {
+  };
+  flutterPlatformViewsController->OnMethodCall(
+      [FlutterMethodCall
+          methodCallWithMethodName:@"create"
+                         arguments:@{@"id" : @2, @"viewType" : @"MockFlutterPlatformView"}],
+      result);  // TODO EMILY: should viewType be backdropFilter?
+
+  XCTAssertNotNil(gMockPlatformView);
+
+  UIView* mockFlutterView = [[[UIView alloc] initWithFrame:CGRectMake(0, 0, 10, 10)] autorelease];
+  flutterPlatformViewsController->SetFlutterView(mockFlutterView);
+  // Create embedded view params
+  flutter::MutatorsStack stack;
+  // Layer tree always pushes a screen scale factor to the stack
+  SkMatrix screenScaleMatrix =
+      SkMatrix::Scale([UIScreen mainScreen].scale, [UIScreen mainScreen].scale);
+  stack.PushTransform(screenScaleMatrix);  // TODO EMILY: change this to PushBackdropFilter
+
+  auto embeddedViewParams =
+      std::make_unique<flutter::EmbeddedViewParams>(screenScaleMatrix, SkSize::Make(10, 10), stack);
+
+  flutterPlatformViewsController->PrerollCompositeEmbeddedView(2, std::move(embeddedViewParams));
+  flutterPlatformViewsController->CompositeEmbeddedView(2);
+  XCTAssertTrue([gMockPlatformView.superview.superview isKindOfClass:[ChildClippingView class]]);
+  ChildClippingView* childClippingView = (ChildClippingView*)gMockPlatformView.superview.superview;
+  [mockFlutterView addSubview:childClippingView];
+
+  [mockFlutterView setNeedsLayout];
+  [mockFlutterView layoutIfNeeded];
+
+  // childClippingView has the CAFilter
+  XCTAssertEqual(1, (int)[childClippingView.layer.filters count]);
+
+  NSObject* gaussianFilter = [childClippingView.layer.filters firstObject];
+  XCTAssertEqual(@(5), [gaussianFilter valueForKey:@"inputRadius"]);
+
+  // No new views were added
+  XCTAssertEqual(0, (int)[gMockPlatformView.subviews count]);
+}
+
+- (void)testChildClippingViewApplyDuplicateBackdropFilter {
+  flutter::FlutterPlatformViewsTestMockPlatformViewDelegate mock_delegate;
+  auto thread_task_runner = CreateNewThread("FlutterPlatformViewsTest");
+  flutter::TaskRunners runners(/*label=*/self.name.UTF8String,
+                               /*platform=*/thread_task_runner,
+                               /*raster=*/thread_task_runner,
+                               /*ui=*/thread_task_runner,
+                               /*io=*/thread_task_runner);
+  auto flutterPlatformViewsController = std::make_shared<flutter::FlutterPlatformViewsController>();
+  auto platform_view = std::make_unique<flutter::PlatformViewIOS>(
+      /*delegate=*/mock_delegate,
+      /*rendering_api=*/flutter::IOSRenderingAPI::kSoftware,
+      /*platform_views_controller=*/flutterPlatformViewsController,
+      /*task_runners=*/runners);
+
+  FlutterPlatformViewsTestMockFlutterPlatformFactory* factory =
+      [[FlutterPlatformViewsTestMockFlutterPlatformFactory new] autorelease];
+  flutterPlatformViewsController->RegisterViewFactory(
+      factory, @"MockFlutterPlatformView",
+      FlutterPlatformViewGestureRecognizersBlockingPolicyEager);
+  FlutterResult result = ^(id result) {
+  };
+  flutterPlatformViewsController->OnMethodCall(
+      [FlutterMethodCall
+          methodCallWithMethodName:@"create"
+                         arguments:@{@"id" : @2, @"viewType" : @"MockFlutterPlatformView"}],
+      result);  // TODO EMILY: should viewType be backdropFilter?
+
+  XCTAssertNotNil(gMockPlatformView);
+
+  UIView* mockFlutterView = [[[UIView alloc] initWithFrame:CGRectMake(0, 0, 10, 10)] autorelease];
+  flutterPlatformViewsController->SetFlutterView(mockFlutterView);
+  // Create embedded view params
+  flutter::MutatorsStack stack;
+  // Layer tree always pushes a screen scale factor to the stack
+  SkMatrix screenScaleMatrix =
+      SkMatrix::Scale([UIScreen mainScreen].scale, [UIScreen mainScreen].scale);
+  stack.PushTransform(screenScaleMatrix);  // TODO EMILY: change this to PushBackdropFilter
+  stack.PushTransform(screenScaleMatrix);
+
+  auto embeddedViewParams =
+      std::make_unique<flutter::EmbeddedViewParams>(screenScaleMatrix, SkSize::Make(10, 10), stack);
+
+  flutterPlatformViewsController->PrerollCompositeEmbeddedView(2, std::move(embeddedViewParams));
+  flutterPlatformViewsController->CompositeEmbeddedView(2);
+  XCTAssertTrue([gMockPlatformView.superview.superview isKindOfClass:[ChildClippingView class]]);
+  ChildClippingView* childClippingView = (ChildClippingView*)gMockPlatformView.superview.superview;
+  [mockFlutterView addSubview:childClippingView];
+
+  [mockFlutterView setNeedsLayout];
+  [mockFlutterView layoutIfNeeded];
+
+  // childClippingView has the CAFilter, no additional filters were added
+  XCTAssertEqual(1, (int)[childClippingView.layer.filters count]);
+
+  NSObject* gaussianFilter = [childClippingView.layer.filters firstObject];
+  XCTAssertEqual(@(5), [gaussianFilter valueForKey:@"inputRadius"]);
+
+  // No new views were added
+  XCTAssertEqual(0, (int)[gMockPlatformView.subviews count]);
+}
+
 - (void)testCompositePlatformView {
   flutter::FlutterPlatformViewsTestMockPlatformViewDelegate mock_delegate;
   auto thread_task_runner = CreateNewThread("FlutterPlatformViewsTest");

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

@@ -48,6 +48,10 @@
 // The parent view handles clipping to its subviews.
 @interface ChildClippingView : UIView
 
+// Adds a blur filter to its layers.
+- (void)applyBackdropFilterWithRadius:
+    (NSNumber*)blurRadius;  // TODO EMILY: is it better to pass an int?
+
 @end
 
 namespace flutter {

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

@@ -56,7 +56,9 @@ void ResetAnchor(CALayer* layer) {
 
 }  // namespace flutter
 
-@implementation ChildClippingView
+@implementation ChildClippingView {
+  NSObject* _gaussianFilter;
+}
 
 // The ChildClippingView's frame is the bounding rect of the platform view. we only want touches to
 // be hit tested and consumed by this view if they are inside the embedded platform view which could
@@ -70,6 +72,45 @@ - (BOOL)pointInside:(CGPoint)point withEvent:(UIEvent*)event {
   return NO;
 }
 
+- (void)applyBackdropFilterWithRadius:(NSNumber*)blurRadius {
+  if (!_gaussianFilter) {
+    UIVisualEffectView* visualEffectView = [[UIVisualEffectView alloc]
+        initWithEffect:[UIBlurEffect effectWithStyle:UIBlurEffectStyleLight]];
+
+    UIView* view = [visualEffectView.subviews firstObject];
+    if (!view) {
+      FML_DLOG(ERROR) << "Apple's API for UIVisualEffectView changed. Update the implementation to "
+                         "access the Gaussian blur filter.";
+      return;
+    }
+
+    _gaussianFilter = [[view.layer.filters firstObject] retain];
+    if (!_gaussianFilter)
+      return;
+
+    FML_DCHECK([[_gaussianFilter valueForKey:@"name"] isEqual:@"gaussianBlur"]);
+    [visualEffectView release];
+  }
+
+  if (![[_gaussianFilter valueForKey:@"inputRadius"] isKindOfClass:[NSNumber class]]) {
+    FML_DLOG(ERROR) << "Apple's API for UIVisualEffectView changed. Update the implementation to "
+                       "access the Gaussian blur filter's properties.";
+    return;
+  }
+
+  if ([[_gaussianFilter valueForKey:@"inputRadius"] isEqual:blurRadius])
+    return;
+
+  [_gaussianFilter setValue:blurRadius forKey:@"inputRadius"];
+  self.layer.filters = @[ _gaussianFilter ];
+}
+
+- (void)dealloc {
+  [_gaussianFilter release];
+  _gaussianFilter = nil;
+  [super dealloc];
+}
+
 @end
 
 @interface FlutterClippingMaskView ()

testing/ios/IosUnitTests/IosUnitTests.xcodeproj/project.pbxproj

@@ -446,6 +446,7 @@
 			buildSettings = {
 				ASSETCATALOG_COMPILER_APPICON_NAME = AppIcon;
 				CODE_SIGN_STYLE = Automatic;
+				DEVELOPMENT_TEAM = "";
 				INFOPLIST_FILE = App/Info.plist;
 				LD_RUNPATH_SEARCH_PATHS = (
 					"$(inherited)",
@@ -466,6 +467,7 @@
 			buildSettings = {
 				ASSETCATALOG_COMPILER_APPICON_NAME = AppIcon;
 				CODE_SIGN_STYLE = Automatic;
+				DEVELOPMENT_TEAM = "";
 				INFOPLIST_FILE = App/Info.plist;
 				LD_RUNPATH_SEARCH_PATHS = (
 					"$(inherited)",