Impeller: the source

since 0.1.0 Backends
Open the live demo · Read the guide · View on GitHub
Regions the guide quotes: fallback (line 39), settings (line 50), read (line 54).
1/// The desktop and mobile path: `flutter_gpu`, through Impeller, the first
2/// backend `openDevice` tries on a native build.
3///
4/// Quoted by `backend_impeller.md` and shown whole in the Source tab.
5library;

7import 'package:flutter/widgets.dart';
8import 'package:flutter3d/flutter3d.dart';
9import 'package:flutter3d_showcase/src/demo/demo.dart';
10import 'package:vector_math/vector_math.dart';

12final class BackendImpellerDemo extends ShowcaseDemo {
late final GraphicsDevice _device;

@override
Scene build(DemoContext context) {
  _device = context.device;
  final Material stone = Material(
    name: 'stone',
    baseColor: Vector4(0.72, 0.5, 0.32, 1.0),
    roughness: 0.6,
  );
  final MeshNode ball = MeshNode(
    DeviceMesh.upload(
      context.device,
      SphereShape(segments: 24, rings: 12).build(),
    ),
    stone,
    name: 'ball',
  );
  return Scene()
    ..add(ball)
    ..add(
      LightNode(name: 'sun', intensity: 3.0)
        ..setLocalForward(Vector3(-0.4, -1.0, -0.3)),
    );
}

// `flutter3d_app`'s native `openDevice` never names a backend. It asks
// `flutter3d_hardware`'s registry to open one, having first made sure
// Impeller and the software rasteriser have both registered themselves:
//
//     ensureGpuBackendRegistered();
//     ensureCpuBackendRegistered();
//     return openRegisteredDevice(width: width, height: height, ...);
//
// Impeller is tried first; the software device is what a native build
// falls back to if flutter_gpu will not start.

@override
RenderSettings settings(DemoContext context) =>
    const RenderSettings(wireframe: true);

String _report(GraphicsDevice device) =>
    'wireframe: ${device.supportsWireframe}\n'
    'blend constant: ${device.supportsBlendColor}\n'
    'max colour attachments: ${device.maxColorAttachments}\n'
    'max anisotropy: ${device.maxAnisotropy}';

@override
Widget? customBody(
  BuildContext buildContext,
  DemoContext context,
) => Container(
  color: const Color(0xFF14161A),
  padding: const EdgeInsets.all(24),
  alignment: Alignment.topLeft,
  child: DefaultTextStyle(
    style: const TextStyle(color: Color(0xFFE8E8EC), fontSize: 16),
    child: Text(
      'On Metal and Vulkan, Impeller answers true to wireframe and can '
      'open more than one colour attachment; on its OpenGL ES path a '
      'second attachment aborts the process outright, which is why '
      'nothing above this asks for one without asking maxColorAttachments '
      'first. It answers false to a blend constant on every platform, '
      'because flutter_gpu\'s own RenderPass has no setter for one.\n\n'
      'What the device actually open right now answers:\n\n'
      '${_report(context.device)}',
    ),
  ),
);

@override
void verify(Scene scene, FrameResult frame) {
  if (frame.drawCalls < 1) {
    throw StateError('the ball was not drawn');
  }
  // Wireframe is the one capability that differs across all three
  // backends. This page asks for it unconditionally; whether the frame
  // actually got it has to match what the device that opened said it
  // could do, whichever backend that turned out to be.
  if (frame.wireframeDeclined != !_device.supportsWireframe) {
    throw StateError(
      'wireframeDeclined disagreed with supportsWireframe for the open '
      'device',
    );
  }
}
99}