Embedding Dart in Your Application

Transcript

1. Embedding Dart in Your Application Don Olmstead Software Engineer | Dart Enthusiast
2. Agenda • Why embed Dart? • Demo • Embedding • Extending • Wrapping up
3. The browser is the platform HTML5 + WebGL ◦ Can make robust 3D applications ◦ Cross-platform ◦ Continually evolving JavaScript
4. Why embed Dart?
5. Why embed Dart?
6. Why embed Dart?
7. The challenge Q: Can Dart be embedded into an application? A: YES!
8. The opportunity
9. Demo time • Goals ◦ Provide an example on how to embed Dart in a native application ◦ Server ▪ Communicate between Dart and C++ ▪ Expose Websockets server ◦ Client ▪ Show real-time updates of the controller's state ▪ Control information through Websockets ▪ UI using Canvas
10. Embedding the VM • Create Isolates ◦ Dart_CreateIsolate • Handle loading of libraries ◦ Dart_SetLibraryTagHandler • Read source code ◦ Resolve uri ◦ Load file from location • Invoke main method ◦ Dart_Invoke
11. Isolate creation Isolate* Isolate::createIsolate(const char* scriptUri, const char* main, bool resolveScript, void* data, char** error) { Dart_Isolate isolate = Dart_CreateIsolate(scriptUri, main, snapshot_buffer, data, error); if (isolate) { Dart_SetLibraryTagHandler(__libraryTagHandler); Dart_Handle uriLibrary = __uriLibrary->load(); // Setup URI library Dart_Handle coreLibrary = __coreLibrary->load(); // Setup core builtin library Dart_Handle ioLibrary = __ioLibrary->load(); // Setup IO library Dart_Handle library = __loadScript(scriptUri, resolveScript, coreLibrary); // Load the script into the isolate Dart_LibraryImportLibrary(library, coreLibrary); // Implicitly import the core library return new Isolate(isolate, library, static_cast<Isolate*>(data)); } return 0; }
12. Complications with embedding • Built in library sources not easily accessible ◦ Have to modify code to access source ◦ Easier to just use a snapshot ▪ Also not intuitive to get at • Core library has to be imported into the isolate ◦ Dart_LibraryImportLibrary
13. Extending the VM • Create a native resolver ◦ Dart_SetNativeResolver ◦ Links string names to native functions • Provide linkage between Dart object and C/C++ object ◦ Handle creation/destruction • Write Dart code that wraps the native code • Respond to calls from Dart
14. A native resolver Dart_NativeFunction Builtin::NativeLookup(Dart_Handle name, int argument_count) { const char* function_name = NULL; Dart_Handle result = Dart_StringToCString(name, &function_name); int num_entries = sizeof(BuiltinEntries) / sizeof(struct NativeEntries); for (int i = 0; i < num_entries; i++) { struct NativeEntries* entry = &(BuiltinEntries[i]); if (!strcmp(function_name, entry->name_)) { return (entry->argument_count_ == argument_count) ? reinterpret_cast<Dart_NativeFunction>(entry->function_) : NULL; } } return NULL; }
15. The Dart side #library('embed:input'); #import('dart:nativewrappers'); class GamePadState extends NativeFieldWrapperClass1 { GamePadState() { _initialize(); } void _initialize() native 'GamePadState_New'; bool get isConnected() native 'GamePadState_IsConnected'; double get leftThumbstickX() native 'GamePadState_GetLeftThumbstickX'; double get leftThumbstickY() native 'GamePadState_GetLeftThumbstickY'; double get rightThumbstickX() native 'GamePadState_GetRightThumbstickX'; double get rightThumbstickY() native 'GamePadState_GetRightThumbstickY'; double get leftTrigger() native 'GamePadState_GetLeftTrigger'; double get rightTrigger() native 'GamePadState_GetRightTrigger'; int get buttons() native 'GamePadState_GetButtons'; }
16. The C++ side (instance lifetime) void GamePadState_New(Dart_NativeArguments args) { Dart_Handle instance = Dart_GetNativeArgument(args, 0); GamePadState* state = new GamePadState(); Dart_SetNativeInstanceField(instance, 0, reinterpret_cast<intptr_t>(state)); Dart_NewWeakPersistentHandle(instance, state, GamePadState_Delete); } void GamePadState_Delete(Dart_Handle handle, void* data) { GamePadState* state = static_cast<GamePadState*>(data); delete state; }
17. The C++ side (using) template <typename T> void getNativeField(Dart_NativeArguments args, int index, T** value) { Dart_Handle handle = Dart_GetNativeArgument(args, index); std::intptr_t ptr; Dart_GetNativeInstanceField(handle, 0, &ptr); *value = reinterpret_cast<T*>(ptr); } void GamePadState_IsConnected(Dart_NativeArguments args) { GamePadState* state = 0; getNativeField(args, 0, &state); Dart_SetReturnValue(args, Dart_NewBoolean(state->isConnected())); }
18. Improving the experience • Move functionality into an auxiliary library ◦ Simplify the embedding experience • Handle common cases ◦ Allow easy loading of built in libraries ◦ Provide a simple way to link in native functions • Create a binding library
19. Thanks for listening! Don Olmstead @don_olmstead +Don Olmstead http://donolmstead.me Code available on Github https://github.com/donny-dont/DartEmbeddingDemo
20. More gamedev with Dart! Game Engine Development with Dart and WebGL November 10th and 11th