| Add a WebAssembly backend for the example 728acaa nandithebull yesterday | 1 | /// Native backend: the V library as a shared object / static archive, reached |
| 2 | /// through `dart:ffi`. |
| 3 | /// |
| 4 | /// Selected by the conditional import in `../vflutter_ffi.dart` on every |
| 5 | /// target except web. The web twin is `backend_web.dart`; the two files must |
| 6 | /// keep the same top-level signatures. |
| 7 | library; |
| 8 | |
| 9 | import 'dart:ffi'; |
| 10 | import 'dart:io'; |
| 11 | import 'dart:isolate'; |
| 12 | import 'dart:typed_data'; |
| 13 | |
| 14 | import 'package:ffi/ffi.dart'; |
| 15 | |
| 16 | import 'fractal_view.dart'; |
| 17 | |
| 18 | const String backendName = 'dart:ffi'; |
| 19 | |
| 20 | /// Isolates are real threads here, and `-gc none` means there is no |
| 21 | /// stop-the-world phase to serialise them. |
| 22 | const bool supportsIsolateParallelism = true; |
| 23 | |
| 24 | const String _libName = 'vflutter'; |
| 25 | |
| 26 | DynamicLibrary _open() { |
| 27 | if (Platform.isMacOS || Platform.isIOS) { |
| 28 | // Static archive linked into the app binary. |
| 29 | return DynamicLibrary.process(); |
| 30 | } |
| 31 | if (Platform.isAndroid || Platform.isLinux) { |
| 32 | return DynamicLibrary.open('lib$_libName.so'); |
| 33 | } |
| 34 | if (Platform.isWindows) { |
| 35 | return DynamicLibrary.open('$_libName.dll'); |
| 36 | } |
| 37 | throw UnsupportedError('vflutter_ffi: unsupported platform'); |
| 38 | } |
| 39 | |
| 40 | final DynamicLibrary _lib = _open(); |
| 41 | |
| 42 | final void Function() _vfInit = |
| 43 | _lib.lookupFunction<Void Function(), void Function()>('vf_init'); |
| 44 | |
| 45 | final int Function(int, int) _vfAdd = |
| 46 | _lib.lookupFunction<Int32 Function(Int32, Int32), int Function(int, int)>( |
| 47 | 'vf_add'); |
| 48 | |
| 49 | final Pointer<Utf8> Function(Pointer<Utf8>) _vfGreet = _lib.lookupFunction< |
| 50 | Pointer<Utf8> Function(Pointer<Utf8>), |
| 51 | Pointer<Utf8> Function(Pointer<Utf8>)>('vf_greet'); |
| 52 | |
| 53 | final void Function(Pointer<Void>) _vfFree = _lib.lookupFunction< |
| 54 | Void Function(Pointer<Void>), void Function(Pointer<Void>)>('vf_free'); |
| 55 | |
| 56 | final void Function(Pointer<Uint8>, int, int, int, double, double, double, int, |
| 57 | int, int) _vfMandelbrot = _lib.lookupFunction< |
| 58 | Void Function(Pointer<Uint8>, Size, Int32, Int32, Double, Double, |
| 59 | Double, Int32, Int32, Int32), |
| 60 | void Function(Pointer<Uint8>, int, int, int, double, double, double, |
| 61 | int, int, int)>('vf_mandelbrot'); |
| 62 | |
| 63 | bool _ready = false; |
| 64 | |
| 65 | bool get isInitialized => _ready; |
| 66 | |
| 67 | /// Loading a shared object is synchronous, so this is only here to match the |
| 68 | /// web backend's contract. Nothing awaits anything. |
| 69 | Future<void> initialize() async => ensureInitialized(); |
| 70 | |
| 71 | void ensureInitialized() { |
| 72 | if (_ready) return; |
| 73 | _vfInit(); |
| 74 | _ready = true; |
| 75 | } |
| 76 | |
| 77 | int add(int a, int b) { |
| 78 | ensureInitialized(); |
| 79 | return _vfAdd(a, b); |
| 80 | } |
| 81 | |
| 82 | String greet(String name) { |
| 83 | ensureInitialized(); |
| 84 | final arg = name.toNativeUtf8(); |
| 85 | Pointer<Utf8> res = nullptr; |
| 86 | try { |
| 87 | res = _vfGreet(arg); |
| 88 | if (res == nullptr) { |
| 89 | throw StateError('vf_greet returned null'); |
| 90 | } |
| 91 | return res.toDartString(); |
| 92 | } finally { |
| 93 | calloc.free(arg); |
| 94 | if (res != nullptr) _vfFree(res.cast()); |
| 95 | } |
| 96 | } |
| 97 | |
| 98 | Future<String> greetAsync(String name) => Isolate.run(() => greet(name)); |
| 99 | |
| 100 | Uint8List renderBand(FractalView view, int y0, int y1) { |
| 101 | ensureInitialized(); |
| 102 | final rows = y1 - y0; |
| 103 | if (rows <= 0) return Uint8List(0); |
| 104 | |
| 105 | final bytes = rows * view.width * 4; |
| 106 | final buf = calloc<Uint8>(bytes); |
| 107 | try { |
| 108 | // `bytes` is the real allocation size, not a restatement of the band: V |
| 109 | // checks it before writing, so an arithmetic slip here is caught there |
| 110 | // rather than becoming a heap overflow. |
| 111 | _vfMandelbrot(buf, bytes, view.width, view.height, view.centerX, |
| 112 | view.centerY, view.scale, view.maxIter, y0, y1); |
| 113 | // Copy out of native memory before it is freed. |
| 114 | return Uint8List.fromList(buf.asTypedList(bytes)); |
| 115 | } finally { |
| 116 | calloc.free(buf); |
| 117 | } |
| 118 | } |
| 119 | |
| 120 | Future<Uint8List> renderParallel(FractalView view, int tiles) async { |
| 121 | ensureInitialized(); |
| 122 | final count = tiles.clamp(1, view.height); |
| 123 | final rowsPer = (view.height / count).ceil(); |
| 124 | |
| 125 | final futures = <Future<Uint8List>>[]; |
| 126 | for (var t = 0; t < count; t++) { |
| 127 | final y0 = t * rowsPer; |
| 128 | final y1 = ((t + 1) * rowsPer).clamp(0, view.height); |
| 129 | if (y0 >= y1) break; |
| 130 | futures.add(Isolate.run(() => renderBand(view, y0, y1))); |
| 131 | } |
| 132 | |
| 133 | final bands = await Future.wait(futures); |
| 134 | final out = Uint8List(view.width * view.height * 4); |
| 135 | var offset = 0; |
| 136 | for (final band in bands) { |
| 137 | out.setRange(offset, offset + band.length, band); |
| 138 | offset += band.length; |
| 139 | } |
| 140 | return out; |
| 141 | } |