Account for root surface transformation on the surfaces managed by th…

…e external view embedder. (flutter#11384)

The earlier design speculated that embedders could affect the same
transformations on the layers post engine compositor presentation but before
final composition.

However, the linked issue points out that this design is not suitable for use
with hardware overlay planes. When rendering to the same, to affect the
transformation before composition, embedders would have to render to an
off-screen render target and then apply the transformation before presentation.
This patch negates the need for that off-screen render pass.

To be clear, the previous architecture is still fully viable. Embedders still
have full control over layer transformations before composition. This is an
optimization for the hardware overlay planes use-case.

Fixes b/139758641

ci/licenses_golden/licenses_flutter

@@ -24,8 +24,6 @@ FILE: ../../../flutter/common/task_runners.cc
 FILE: ../../../flutter/common/task_runners.h
 FILE: ../../../flutter/flow/compositor_context.cc
 FILE: ../../../flutter/flow/compositor_context.h
-FILE: ../../../flutter/flow/debug_print.cc
-FILE: ../../../flutter/flow/debug_print.h
 FILE: ../../../flutter/flow/embedded_views.cc
 FILE: ../../../flutter/flow/embedded_views.h
 FILE: ../../../flutter/flow/instrumentation.cc
@@ -849,10 +847,15 @@ FILE: ../../../flutter/shell/platform/embedder/embedder_task_runner.h
 FILE: ../../../flutter/shell/platform/embedder/embedder_thread_host.cc
 FILE: ../../../flutter/shell/platform/embedder/embedder_thread_host.h
 FILE: ../../../flutter/shell/platform/embedder/fixtures/compositor.png
+FILE: ../../../flutter/shell/platform/embedder/fixtures/compositor_root_surface_xformation.png
 FILE: ../../../flutter/shell/platform/embedder/fixtures/compositor_software.png
 FILE: ../../../flutter/shell/platform/embedder/fixtures/compositor_with_platform_layer_on_bottom.png
 FILE: ../../../flutter/shell/platform/embedder/fixtures/compositor_with_root_layer_only.png
+FILE: ../../../flutter/shell/platform/embedder/fixtures/gradient.png
+FILE: ../../../flutter/shell/platform/embedder/fixtures/gradient_xform.png
 FILE: ../../../flutter/shell/platform/embedder/fixtures/main.dart
+FILE: ../../../flutter/shell/platform/embedder/fixtures/scene_without_custom_compositor.png
+FILE: ../../../flutter/shell/platform/embedder/fixtures/scene_without_custom_compositor_with_xform.png
 FILE: ../../../flutter/shell/platform/embedder/platform_view_embedder.cc
 FILE: ../../../flutter/shell/platform/embedder/platform_view_embedder.h
 FILE: ../../../flutter/shell/platform/embedder/vsync_waiter_embedder.cc

flow/BUILD.gn

@@ -12,8 +12,6 @@ source_set("flow") {
   sources = [
     "compositor_context.cc",
     "compositor_context.h",
-    "debug_print.cc",
-    "debug_print.h",
     "embedded_views.cc",
     "embedded_views.h",
     "instrumentation.cc",

lib/ui/painting/image_decoder_unittests.cc

@@ -19,7 +19,8 @@ class TestIOManager final : public IOManager {
  public:
   TestIOManager(fml::RefPtr<fml::TaskRunner> task_runner,
                 bool has_gpu_context = true)
-      : gl_context_(has_gpu_context ? gl_surface_.CreateGrContext() : nullptr),
+      : gl_surface_(SkISize::Make(1, 1)),
+        gl_context_(has_gpu_context ? gl_surface_.CreateGrContext() : nullptr),
         weak_gl_context_factory_(
             has_gpu_context ? std::make_unique<fml::WeakPtrFactory<GrContext>>(
                                   gl_context_.get())

shell/common/shell_test.cc

@@ -234,7 +234,8 @@ void ShellTest::AddNativeCallback(std::string name,
 
 ShellTestPlatformView::ShellTestPlatformView(PlatformView::Delegate& delegate,
                                              TaskRunners task_runners)
-    : PlatformView(delegate, std::move(task_runners)) {}
+    : PlatformView(delegate, std::move(task_runners)),
+      gl_surface_(SkISize::Make(800, 600)) {}
 
 ShellTestPlatformView::~ShellTestPlatformView() = default;
 

shell/platform/embedder/BUILD.gn

@@ -85,9 +85,14 @@ test_fixtures("fixtures") {
   dart_main = "fixtures/main.dart"
   fixtures = [
     "fixtures/compositor.png",
+    "fixtures/gradient.png",
+    "fixtures/gradient_xform.png",
     "fixtures/compositor_software.png",
     "fixtures/compositor_with_platform_layer_on_bottom.png",
     "fixtures/compositor_with_root_layer_only.png",
+    "fixtures/compositor_root_surface_xformation.png",
+    "fixtures/scene_without_custom_compositor.png",
+    "fixtures/scene_without_custom_compositor_with_xform.png",
   ]
 }
 
@@ -119,6 +124,7 @@ if (current_toolchain == host_toolchain) {
       "$flutter_root/runtime",
       "$flutter_root/testing:dart",
       "$flutter_root/testing:opengl",
+      "$flutter_root/testing:skia",
       "//third_party/skia",
       "//third_party/tonic",
     ]

shell/platform/embedder/embedder.cc

@@ -171,6 +171,13 @@ InferOpenGLPlatformViewCreationCallback(
                                    transformation.pers2    //
           );
         };
+
+    // If there is an external view embedder, ask it to apply the surface
+    // transformation to its surfaces as well.
+    if (external_view_embedder) {
+      external_view_embedder->SetSurfaceTransformationCallback(
+          gl_surface_transformation_callback);
+    }
   }
 
   flutter::GPUSurfaceGLDelegate::GLProcResolver gl_proc_resolver = nullptr;
@@ -296,13 +303,13 @@ static sk_sp<SkSurface> MakeSkSurfaceFromBackingStore(
       SkSurfaceProps::InitType::kLegacyFontHost_InitType);
 
   auto surface = SkSurface::MakeFromBackendTexture(
-      context,                   // context
-      backend_texture,           // back-end texture
-      kTopLeft_GrSurfaceOrigin,  // surface origin
-      1,                         // sample count
-      kN32_SkColorType,          // color type
-      SkColorSpace::MakeSRGB(),  // color space
-      &surface_properties,       // surface properties
+      context,                      // context
+      backend_texture,              // back-end texture
+      kBottomLeft_GrSurfaceOrigin,  // surface origin
+      1,                            // sample count
+      kN32_SkColorType,             // color type
+      SkColorSpace::MakeSRGB(),     // color space
+      &surface_properties,          // surface properties
       static_cast<SkSurface::TextureReleaseProc>(
           texture->destruction_callback),  // release proc
       texture->user_data                   // release context
@@ -337,12 +344,12 @@ static sk_sp<SkSurface> MakeSkSurfaceFromBackingStore(
       SkSurfaceProps::InitType::kLegacyFontHost_InitType);
 
   auto surface = SkSurface::MakeFromBackendRenderTarget(
-      context,                   //  context
-      backend_render_target,     // backend render target
-      kTopLeft_GrSurfaceOrigin,  // surface origin
-      kN32_SkColorType,          // color type
-      SkColorSpace::MakeSRGB(),  // color space
-      &surface_properties,       // surface properties
+      context,                      //  context
+      backend_render_target,        // backend render target
+      kBottomLeft_GrSurfaceOrigin,  // surface origin
+      kN32_SkColorType,             // color type
+      SkColorSpace::MakeSRGB(),     // color space
+      &surface_properties,          // surface properties
       static_cast<SkSurface::RenderTargetReleaseProc>(
           framebuffer->destruction_callback),  // release proc
       framebuffer->user_data                   // release context

shell/platform/embedder/embedder.h

@@ -282,6 +282,14 @@ typedef struct {
   bool fbo_reset_after_present;
   /// The transformation to apply to the render target before any rendering
   /// operations. This callback is optional.
+  /// @attention      When using a custom compositor, the layer offset and sizes
+  ///                 will be affected by this transformation. It will be
+  ///                 embedder responsibility to render contents at the
+  ///                 transformed offset and size. This is useful for embedders
+  ///                 that want to render transformed contents directly into
+  ///                 hardware overlay planes without having to apply extra
+  ///                 transformations to layer contents (which may necessitate
+  ///                 an expensive off-screen render pass).
   TransformationCallback surface_transformation;
   ProcResolver gl_proc_resolver;
   /// When the embedder specifies that a texture has a frame available, the