Provide a runtime switch for selecting SkParagraph text layout (#23474)

common/settings.h

@@ -152,6 +152,9 @@ struct Settings {
   // Font settings
   bool use_test_fonts = false;
 
+  // Selects the SkParagraph implementation of the text layout engine.
+  bool enable_skparagraph = false;
+
   // All shells in the process share the same VM. The last shell to shutdown
   // should typically shut down the VM as well. However, applications depend on
   // the behavior of "warming-up" the VM by creating a shell that does not do

lib/ui/text/paragraph_builder.cc

@@ -295,14 +295,18 @@ ParagraphBuilder::ParagraphBuilder(
                                         ->client()
                                         ->GetFontCollection();
 
+  typedef std::unique_ptr<txt::ParagraphBuilder> (*ParagraphBuilderFactory)(
+      const txt::ParagraphStyle& style,
+      std::shared_ptr<txt::FontCollection> font_collection);
+  ParagraphBuilderFactory factory = txt::ParagraphBuilder::CreateTxtBuilder;
+
 #if FLUTTER_ENABLE_SKSHAPER
-#define FLUTTER_PARAGRAPH_BUILDER txt::ParagraphBuilder::CreateSkiaBuilder
-#else
-#define FLUTTER_PARAGRAPH_BUILDER txt::ParagraphBuilder::CreateTxtBuilder
+  if (UIDartState::Current()->enable_skparagraph()) {
+    factory = txt::ParagraphBuilder::CreateSkiaBuilder;
+  }
 #endif
 
-  m_paragraphBuilder =
-      FLUTTER_PARAGRAPH_BUILDER(style, font_collection.GetFontCollection());
+  m_paragraphBuilder = factory(style, font_collection.GetFontCollection());
 }
 
 ParagraphBuilder::~ParagraphBuilder() = default;

lib/ui/ui_dart_state.cc

@@ -28,7 +28,8 @@ UIDartState::UIDartState(
     UnhandledExceptionCallback unhandled_exception_callback,
     std::shared_ptr<IsolateNameServer> isolate_name_server,
     bool is_root_isolate,
-    std::shared_ptr<VolatilePathTracker> volatile_path_tracker)
+    std::shared_ptr<VolatilePathTracker> volatile_path_tracker,
+    bool enable_skparagraph)
     : task_runners_(std::move(task_runners)),
       add_callback_(std::move(add_callback)),
       remove_callback_(std::move(remove_callback)),
@@ -43,7 +44,8 @@ UIDartState::UIDartState(
       logger_prefix_(std::move(logger_prefix)),
       is_root_isolate_(is_root_isolate),
       unhandled_exception_callback_(unhandled_exception_callback),
-      isolate_name_server_(std::move(isolate_name_server)) {
+      isolate_name_server_(std::move(isolate_name_server)),
+      enable_skparagraph_(enable_skparagraph) {
   AddOrRemoveTaskObserver(true /* add */);
 }
 
@@ -185,4 +187,8 @@ void UIDartState::ReportUnhandledException(const std::string& error,
                  << stack_trace;
 }
 
+bool UIDartState::enable_skparagraph() const {
+  return enable_skparagraph_;
+}
+
 }  // namespace flutter

lib/ui/ui_dart_state.h

@@ -77,6 +77,8 @@ class UIDartState : public tonic::DartState {
   void ReportUnhandledException(const std::string& error,
                                 const std::string& stack_trace);
 
+  bool enable_skparagraph() const;
+
   template <class T>
   static flutter::SkiaGPUObject<T> CreateGPUObject(sk_sp<T> object) {
     if (!object) {
@@ -103,7 +105,8 @@ class UIDartState : public tonic::DartState {
               UnhandledExceptionCallback unhandled_exception_callback,
               std::shared_ptr<IsolateNameServer> isolate_name_server,
               bool is_root_isolate_,
-              std::shared_ptr<VolatilePathTracker> volatile_path_tracker);
+              std::shared_ptr<VolatilePathTracker> volatile_path_tracker,
+              bool enable_skparagraph);
 
   ~UIDartState() override;
 
@@ -136,6 +139,7 @@ class UIDartState : public tonic::DartState {
   tonic::DartMicrotaskQueue microtask_queue_;
   UnhandledExceptionCallback unhandled_exception_callback_;
   const std::shared_ptr<IsolateNameServer> isolate_name_server_;
+  const bool enable_skparagraph_;
 
   void AddOrRemoveTaskObserver(bool add);
 };

runtime/dart_isolate.cc

@@ -271,7 +271,8 @@ DartIsolate::DartIsolate(
                   settings.unhandled_exception_callback,
                   DartVMRef::GetIsolateNameServer(),
                   is_root_isolate,
-                  std::move(volatile_path_tracker)),
+                  std::move(volatile_path_tracker),
+                  settings.enable_skparagraph),
       may_insecurely_connect_to_all_domains_(
           settings.may_insecurely_connect_to_all_domains),
       domain_network_policy_(settings.domain_network_policy) {

shell/common/switches.cc

@@ -378,6 +378,9 @@ Settings SettingsFromCommandLine(const fml::CommandLine& command_line) {
   settings.use_test_fonts =
       command_line.HasOption(FlagForSwitch(Switch::UseTestFonts));
 
+  settings.enable_skparagraph =
+      command_line.HasOption(FlagForSwitch(Switch::EnableSkParagraph));
+
   std::string all_dart_flags;
   if (command_line.GetOptionValue(FlagForSwitch(Switch::DartFlags),
                                   &all_dart_flags)) {

shell/common/switches.h

@@ -202,6 +202,9 @@ DEF_SWITCH(
 DEF_SWITCH(OldGenHeapSize,
            "old-gen-heap-size",
            "The size limit in megabytes for the Dart VM old gen heap space.")
+DEF_SWITCH(EnableSkParagraph,
+           "enable-skparagraph",
+           "Selects the SkParagraph implementation of the text layout engine.")
 
 DEF_SWITCHES_END
 

shell/platform/android/io/flutter/embedding/engine/loader/FlutterLoader.java

@@ -33,6 +33,8 @@ public class FlutterLoader {
 
   private static final String OLD_GEN_HEAP_SIZE_META_DATA_KEY =
       "io.flutter.embedding.android.OldGenHeapSize";
+  private static final String ENABLE_SKPARAGRAPH_META_DATA_KEY =
+      "io.flutter.embedding.android.EnableSkParagraph";
 
   // Must match values in flutter::switches
   static final String AOT_SHARED_LIBRARY_NAME = "aot-shared-library-name";
@@ -263,6 +265,10 @@ public class FlutterLoader {
 
       shellArgs.add("--old-gen-heap-size=" + oldGenHeapSizeMegaBytes);
 
+      if (metaData != null && metaData.getBoolean(ENABLE_SKPARAGRAPH_META_DATA_KEY)) {
+        shellArgs.add("--enable-skparagraph");
+      }
+
       long initTimeMillis = SystemClock.uptimeMillis() - initStartTimestampMillis;
 
       flutterJNI.init(

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

@@ -141,6 +141,10 @@ flutter::Settings FLTDefaultSettingsForBundle(NSBundle* bundle) {
   settings.domain_network_policy =
       [FlutterDartProject domainNetworkPolicy:appTransportSecurity].UTF8String;
 
+  // SkParagraph text layout library
+  NSNumber* enableSkParagraph = [mainBundle objectForInfoDictionaryKey:@"FLTEnableSkParagraph"];
+  settings.enable_skparagraph = (enableSkParagraph != nil) ? enableSkParagraph.boolValue : false;
+
 #if FLUTTER_RUNTIME_MODE == FLUTTER_RUNTIME_MODE_DEBUG
   // There are no ownership concerns here as all mappings are owned by the
   // embedder and not the engine.