Allow FlutterViewController to specify whether its FlutterView is opaque (flutter/engine#6570)

* Allow FlutterViewController to specify whether its FlutterView is opaque

engine/src/flutter/shell/platform/darwin/ios/framework/Headers/FlutterViewController.h

@@ -93,6 +93,15 @@ FLUTTER_EXPORT
  */
 @property(strong, nonatomic) UIView* splashScreenView;
 
+/**
+ * Controls whether the created view will be opaque or not.
+ *
+ * Default is `YES`.  Note that setting this to `NO` may negatively impact performance
+ * when using hardware acceleration, and toggling this will trigger a re-layout of the
+ * view.
+ */
+@property(nonatomic, getter=isViewOpaque) BOOL viewOpaque;
+
 @end
 
 #endif  // FLUTTER_FLUTTERVIEWCONTROLLER_H_

engine/src/flutter/shell/platform/darwin/ios/framework/Source/FlutterView.h

@@ -9,10 +9,25 @@
 
 #include <memory>
 
+#include "flutter/fml/memory/weak_ptr.h"
+#include "flutter/shell/common/shell.h"
 #include "flutter/shell/platform/darwin/ios/ios_surface.h"
 
+@protocol FlutterScreenshotDelegate <NSObject>
+
+- (shell::Rasterizer::Screenshot)takeScreenshot:(shell::Rasterizer::ScreenshotType)type
+                                asBase64Encoded:(BOOL)base64Encode;
+
+@end
+
 @interface FlutterView : UIView
 
+- (instancetype)init NS_UNAVAILABLE;
+- (instancetype)initWithFrame:(CGRect)frame NS_UNAVAILABLE;
+- (instancetype)initWithCoder:(NSCoder*)aDecoder NS_UNAVAILABLE;
+
+- (instancetype)initWithDelegate:(id<FlutterScreenshotDelegate>)delegate
+                          opaque:(BOOL)opaque NS_DESIGNATED_INITIALIZER;
 - (std::unique_ptr<shell::IOSSurface>)createSurface;
 
 @end

engine/src/flutter/shell/platform/darwin/ios/framework/Source/FlutterView.mm

@@ -12,8 +12,6 @@
 #include "flutter/fml/trace_event.h"
 #include "flutter/shell/common/platform_view.h"
 #include "flutter/shell/common/rasterizer.h"
-#include "flutter/shell/common/shell.h"
-#include "flutter/shell/platform/darwin/ios/framework/Source/FlutterViewController_Internal.h"
 #include "flutter/shell/platform/darwin/ios/ios_surface_gl.h"
 #include "flutter/shell/platform/darwin/ios/ios_surface_software.h"
 #include "third_party/skia/include/utils/mac/SkCGUtils.h"
@@ -24,28 +22,42 @@
 
 @implementation FlutterView
 
-- (FlutterViewController*)flutterViewController {
-  // Find the first view controller in the responder chain and see if it is a FlutterViewController.
-  for (UIResponder* responder = self.nextResponder; responder != nil;
-       responder = responder.nextResponder) {
-    if ([responder isKindOfClass:[UIViewController class]]) {
-      if ([responder isKindOfClass:[FlutterViewController class]]) {
-        return reinterpret_cast<FlutterViewController*>(responder);
-      } else {
-        // Should only happen if a non-FlutterViewController tries to somehow (via dynamic class
-        // resolution or reparenting) set a FlutterView as its view.
-        return nil;
-      }
-    }
+id<FlutterScreenshotDelegate> _delegate;
+
+- (instancetype)init {
+  @throw([NSException exceptionWithName:@"FlutterView must initWithDelegate"
+                                 reason:nil
+                               userInfo:nil]);
+}
+
+- (instancetype)initWithFrame:(CGRect)frame {
+  @throw([NSException exceptionWithName:@"FlutterView must initWithDelegate"
+                                 reason:nil
+                               userInfo:nil]);
+}
+
+- (instancetype)initWithCoder:(NSCoder*)aDecoder {
+  @throw([NSException exceptionWithName:@"FlutterView must initWithDelegate"
+                                 reason:nil
+                               userInfo:nil]);
+}
+
+- (instancetype)initWithDelegate:(id<FlutterScreenshotDelegate>)delegate opaque:(BOOL)opaque {
+  FML_DCHECK(delegate) << "Delegate must not be nil.";
+  self = [super initWithFrame:CGRectNull];
+
+  if (self) {
+    _delegate = delegate;
+    self.layer.opaque = opaque;
   }
-  return nil;
+
+  return self;
 }
 
 - (void)layoutSubviews {
   if ([self.layer isKindOfClass:[CAEAGLLayer class]]) {
     CAEAGLLayer* layer = reinterpret_cast<CAEAGLLayer*>(self.layer);
     layer.allowsGroupOpacity = YES;
-    layer.opaque = YES;
     CGFloat screenScale = [UIScreen mainScreen].scale;
     layer.contentsScale = screenScale;
     layer.rasterizationScale = screenScale;
@@ -84,16 +96,8 @@
     return;
   }
 
-  FlutterViewController* controller = [self flutterViewController];
-
-  if (controller == nil) {
-    return;
-  }
-
-  auto& shell = [controller shell];
-
-  auto screenshot = shell.Screenshot(shell::Rasterizer::ScreenshotType::UncompressedImage,
-                                     false /* base64 encode */);
+  auto screenshot = [_delegate takeScreenshot:shell::Rasterizer::ScreenshotType::UncompressedImage
+                              asBase64Encoded:NO];
 
   if (!screenshot.data || screenshot.data->isEmpty() || screenshot.frame_size.isEmpty()) {
     return;

engine/src/flutter/shell/platform/darwin/ios/framework/Source/FlutterViewController.mm

@@ -22,7 +22,7 @@
 #include "flutter/shell/platform/darwin/ios/framework/Source/platform_message_response_darwin.h"
 #include "flutter/shell/platform/darwin/ios/platform_view_ios.h"
 
-@interface FlutterViewController () <FlutterTextInputDelegate>
+@interface FlutterViewController () <FlutterTextInputDelegate, FlutterScreenshotDelegate>
 @property(nonatomic, readonly) NSMutableDictionary* pluginPublications;
 @end
 
@@ -58,6 +58,7 @@
   blink::ViewportMetrics _viewportMetrics;
   int64_t _nextTextureId;
   BOOL _initialized;
+  BOOL _viewOpaque;
 
   fml::scoped_nsobject<FlutterObservatoryPublisher> _publisher;
 }
@@ -75,6 +76,8 @@
     else
       _dartProject.reset([projectOrNil retain]);
 
+    self.viewOpaque = YES;
+
     [self performCommonViewControllerInitialization];
   }
 
@@ -146,7 +149,7 @@
                                   _threadHost.io_thread->GetTaskRunner()           // io
   );
 
-  _flutterView.reset([[FlutterView alloc] init]);
+  _flutterView.reset([[FlutterView alloc] initWithDelegate:self opaque:self.isViewOpaque]);
 
   // Lambda captures by pointers to ObjC objects are fine here because the create call is
   // synchronous.
@@ -180,6 +183,18 @@
   return true;
 }
 
+- (BOOL)isViewOpaque {
+  return _viewOpaque;
+}
+
+- (void)viewOpaque:(BOOL)value {
+  _viewOpaque = value;
+  if (_flutterView.get().layer.opaque != value) {
+    _flutterView.get().layer.opaque = value;
+    [_flutterView.get().layer setNeedsLayout];
+  }
+}
+
 - (void)setupChannels {
   _localizationChannel.reset([[FlutterMethodChannel alloc]
          initWithName:@"flutter/localization"
@@ -840,6 +855,14 @@ static blink::PointerData::DeviceKind DeviceKindFromTouchType(UITouch* touch) {
                               arguments:@[ @(client), actionString ]];
 }
 
+#pragma mark - Screenshot Delegate
+
+- (shell::Rasterizer::Screenshot)takeScreenshot:(shell::Rasterizer::ScreenshotType)type
+                                asBase64Encoded:(BOOL)base64Encode {
+  FML_DCHECK(_shell) << "Cannot takeScreenshot without a shell";
+  return _shell->Screenshot(type, base64Encode);
+}
+
 #pragma mark - Orientation updates
 
 - (void)onOrientationPreferencesUpdated:(NSNotification*)notification {