It looks like this pull request may not have tests. Please make sure to add tests or get an explicit test exemption before merging.

If you are not sure if you need tests, consider this rule of thumb: the purpose of a test is to make sure someone doesn't accidentally revert the fix. Ask yourself, is there anything in your PR that you feel it is important we not accidentally revert back to how it was before your fix?

Reviewers: Read the Tree Hygiene page and make sure this patch meets those guidelines before LGTMing. If you believe this PR qualifies for a test exemption, contact "@test-exemption-reviewer" in the #hackers channel in Discord (don't just cc them here, they won't see it!). The test exemption team is a small volunteer group, so all reviewers should feel empowered to ask for tests, without delegating that responsibility entirely to the test exemption group.

@xiaowei-guan this PR doesn't have a test, unfortunately I'm not that familiar with this code so I can't give you a pointer on the best way to test it and I'm not readily seeing unit testing set up here. I cannot approve it without some sort of test though.

OK, I will add unit test later.

For a test, these might be useful resources for prior art you can copy:

1. This is the C++ code that launches the engine to render some content using OpenGL + Impeller:

   flutter/engine/src/flutter/shell/platform/embedder/tests/embedder_gl_unittests.cc

   Lines 4773 to 4830 in 9b9f997

   	TEST_F(EmbedderTest, CanRenderWithImpellerOpenGL) {
   	auto& context = GetEmbedderContext<EmbedderTestContextGL>();
   	EmbedderConfigBuilder builder(context);
   	bool present_called = false;
   	context.SetGLPresentCallback(
   	[&present_called](FlutterPresentInfo present_info) {
   	present_called = true;
   	});
   	builder.AddCommandLineArgument("--enable-impeller");
   	builder.SetDartEntrypoint("render_impeller_test");
   	builder.SetSurface(DlISize(800, 600));
   	builder.SetCompositor();
   	builder.SetRenderTargetType(
   	EmbedderTestBackingStoreProducer::RenderTargetType::kOpenGLFramebuffer);
   	auto rendered_scene = context.GetNextSceneImage();
   	auto engine = builder.LaunchEngine();
   	ASSERT_TRUE(engine.is_valid());
   	// Bind to an arbitrary FBO in order to verify that Impeller binds to the
   	// provided FBO during rendering.
   	typedef void (*glGenFramebuffersProc)(GLsizei n, GLuint* ids);
   	typedef void (*glBindFramebufferProc)(GLenum target, GLuint framebuffer);
   	auto glGenFramebuffers = reinterpret_cast<glGenFramebuffersProc>(
   	context.GLGetProcAddress("glGenFramebuffers"));
   	auto glBindFramebuffer = reinterpret_cast<glBindFramebufferProc>(
   	context.GLGetProcAddress("glBindFramebuffer"));
   	const flutter::Shell& shell = ToEmbedderEngine(engine.get())->GetShell();
   	fml::AutoResetWaitableEvent raster_event;
   	shell.GetTaskRunners().GetRasterTaskRunner()->PostTask([&] {
   	GLuint fbo;
   	glGenFramebuffers(1, &fbo);
   	glBindFramebuffer(GL_FRAMEBUFFER, fbo);
   	raster_event.Signal();
   	});
   	raster_event.Wait();
   	// Send a window metrics events so frames may be scheduled.
   	FlutterWindowMetricsEvent event = {};
   	event.struct_size = sizeof(event);
   	event.width = 800;
   	event.height = 600;
   	event.pixel_ratio = 1.0;
   	ASSERT_EQ(FlutterEngineSendWindowMetricsEvent(engine.get(), &event),
   	kSuccess);
   	ASSERT_TRUE(ImageMatchesFixture(
   	FixtureNameForBackend(EmbedderTestContextType::kOpenGLContext,
   	"impeller_test.png"),
   	rendered_scene));
   	// The scene will be rendered by the compositor, and the surface present
   	// callback should not be invoked.
   	ASSERT_FALSE(present_called);
   	}

2. This is the Dart code that renders some content:

   flutter/engine/src/flutter/shell/platform/embedder/fixtures/main.dart

   Lines 1560 to 1576 in 9b9f997

   	@pragma('vm:entry-point')
   	// ignore: non_constant_identifier_names
   	void render_impeller_test() {
   	PlatformDispatcher.instance.onBeginFrame = (Duration duration) {
   	final builder = SceneBuilder();
   	builder.pushOffset(0.0, 0.0);
   	final paint = Paint();
   	paint.color = const Color.fromARGB(255, 0, 0, 255);
   	final baseRecorder = PictureRecorder();
   	final canvas = Canvas(baseRecorder);
   	canvas.drawPaint(Paint()..color = const Color.fromARGB(255, 255, 0, 0));
   	canvas.drawRect(const Rect.fromLTRB(20.0, 20.0, 200.0, 150.0), paint);
   	builder.addPicture(Offset.zero, baseRecorder.endRecording());
   	builder.pop();
   	PlatformDispatcher.instance.views.first.render(builder.build());
   	};
   	PlatformDispatcher.instance.scheduleFrame();

3. This is the snapshot of the expected test output: https://github.com/flutter/flutter/blob/9b9f9975c76a1474b96426d22cd34cc589ad6f53/engine/src/flutter/shell/platform/embedder/fixtures/impeller_test.png

@xiaowei-guan this PR doesn't have a test, unfortunately I'm not that familiar with this code so I can't give you a pointer on the best way to test it and I'm not readily seeing unit testing set up here. I cannot approve it without some sort of test though.

@gaaclarke I have added a unit test for rendering a impeller texture.

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Rebased

An existing Git SHA, 8004628ca0401a70bec720d16800ae8b71f43eae, was detected, and no actions were taken.

To re-trigger presubmits after closing or re-opeing a PR, or pushing a HEAD commit (i.e. with --force) that already was pushed before, push a blank commit (git commit --allow-empty -m "Trigger Build") or rebase to continue.

Notes from google testing: There is a merge conflict in the PR that cannot be rolled cleanly, please rebase the PR.

We just rebased, but I'll try again.

jinx

autosubmit label was removed for flutter/flutter/181656, because - The status or check suite Google testing has failed. Please fix the issues identified (or deflake) before re-applying this label.

autosubmit label was removed for flutter/flutter/181656, because - The status or check suite Google testing has failed. Please fix the issues identified (or deflake) before re-applying this label.

Rebase again

I have rebased locally against upstream/master and forced pushed, but the g3 conflict persists. Could a maintainer help check if this is an internal sync issue?

It's reporting a merge conflict, I tried to hit the button to attempt again but no luck. There is zero feedback about where the merge conflict is happening. I'll try reaching out to someone that works on this tool.