Add support for multiple top-level windows on Windows

ci/licenses_golden/excluded_files

@@ -398,6 +398,7 @@
 ../../../flutter/shell/platform/windows/client_wrapper/flutter_engine_unittests.cc
 ../../../flutter/shell/platform/windows/client_wrapper/flutter_view_controller_unittests.cc
 ../../../flutter/shell/platform/windows/client_wrapper/flutter_view_unittests.cc
+../../../flutter/shell/platform/windows/client_wrapper/flutter_window_controller_unittests.cc
 ../../../flutter/shell/platform/windows/client_wrapper/plugin_registrar_windows_unittests.cc
 ../../../flutter/shell/platform/windows/client_wrapper/testing
 ../../../flutter/shell/platform/windows/compositor_opengl_unittests.cc

ci/licenses_golden/licenses_flutter

@@ -44407,6 +44407,7 @@ ORIGIN: ../../../flutter/shell/platform/common/client_wrapper/include/flutter/st
 ORIGIN: ../../../flutter/shell/platform/common/client_wrapper/include/flutter/standard_message_codec.h + ../../../flutter/LICENSE
 ORIGIN: ../../../flutter/shell/platform/common/client_wrapper/include/flutter/standard_method_codec.h + ../../../flutter/LICENSE
 ORIGIN: ../../../flutter/shell/platform/common/client_wrapper/include/flutter/texture_registrar.h + ../../../flutter/LICENSE
+ORIGIN: ../../../flutter/shell/platform/common/client_wrapper/include/flutter/windowing.h + ../../../flutter/LICENSE
 ORIGIN: ../../../flutter/shell/platform/common/client_wrapper/plugin_registrar.cc + ../../../flutter/LICENSE
 ORIGIN: ../../../flutter/shell/platform/common/client_wrapper/standard_codec.cc + ../../../flutter/LICENSE
 ORIGIN: ../../../flutter/shell/platform/common/client_wrapper/texture_registrar_impl.h + ../../../flutter/LICENSE
@@ -47286,6 +47287,7 @@ FILE: ../../../flutter/shell/platform/common/client_wrapper/include/flutter/stan
 FILE: ../../../flutter/shell/platform/common/client_wrapper/include/flutter/standard_message_codec.h
 FILE: ../../../flutter/shell/platform/common/client_wrapper/include/flutter/standard_method_codec.h
 FILE: ../../../flutter/shell/platform/common/client_wrapper/include/flutter/texture_registrar.h
+FILE: ../../../flutter/shell/platform/common/client_wrapper/include/flutter/windowing.h
 FILE: ../../../flutter/shell/platform/common/client_wrapper/plugin_registrar.cc
 FILE: ../../../flutter/shell/platform/common/client_wrapper/standard_codec.cc
 FILE: ../../../flutter/shell/platform/common/client_wrapper/texture_registrar_impl.h
@@ -48000,11 +48002,18 @@ FILE: ../../../flutter/shell/platform/windows/accessibility_plugin.cc
 FILE: ../../../flutter/shell/platform/windows/accessibility_plugin.h
 FILE: ../../../flutter/shell/platform/windows/client_wrapper/flutter_engine.cc
 FILE: ../../../flutter/shell/platform/windows/client_wrapper/flutter_view_controller.cc
+FILE: ../../../flutter/shell/platform/windows/client_wrapper/flutter_win32_window.cc
+FILE: ../../../flutter/shell/platform/windows/client_wrapper/flutter_window_controller.cc
 FILE: ../../../flutter/shell/platform/windows/client_wrapper/include/flutter/dart_project.h
 FILE: ../../../flutter/shell/platform/windows/client_wrapper/include/flutter/flutter_engine.h
 FILE: ../../../flutter/shell/platform/windows/client_wrapper/include/flutter/flutter_view.h
 FILE: ../../../flutter/shell/platform/windows/client_wrapper/include/flutter/flutter_view_controller.h
+FILE: ../../../flutter/shell/platform/windows/client_wrapper/include/flutter/flutter_win32_window.h
+FILE: ../../../flutter/shell/platform/windows/client_wrapper/include/flutter/flutter_window_controller.h
 FILE: ../../../flutter/shell/platform/windows/client_wrapper/include/flutter/plugin_registrar_windows.h
+FILE: ../../../flutter/shell/platform/windows/client_wrapper/include/flutter/win32_window.h
+FILE: ../../../flutter/shell/platform/windows/client_wrapper/include/flutter/win32_wrapper.h
+FILE: ../../../flutter/shell/platform/windows/client_wrapper/win32_window.cc
 FILE: ../../../flutter/shell/platform/windows/compositor.h
 FILE: ../../../flutter/shell/platform/windows/compositor_opengl.cc
 FILE: ../../../flutter/shell/platform/windows/compositor_opengl.h

shell/platform/common/client_wrapper/core_wrapper_files.gni

@@ -25,6 +25,7 @@ core_cpp_client_wrapper_includes =
                     "include/flutter/standard_message_codec.h",
                     "include/flutter/standard_method_codec.h",
                     "include/flutter/texture_registrar.h",
+                    "include/flutter/windowing.h",
                   ],
                   "abspath")
 

shell/platform/common/client_wrapper/include/flutter/windowing.h

@@ -0,0 +1,148 @@
+// Copyright 2013 The Flutter Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef FLUTTER_SHELL_PLATFORM_COMMON_CLIENT_WRAPPER_INCLUDE_FLUTTER_WINDOWING_H_
+#define FLUTTER_SHELL_PLATFORM_COMMON_CLIENT_WRAPPER_INCLUDE_FLUTTER_WINDOWING_H_
+
+#include <optional>
+
+namespace flutter {
+
+// The unique identifier for a view.
+using FlutterViewId = int64_t;
+
+// A point (x, y) in 2D space for window positioning.
+struct WindowPoint {
+  int x{0};
+  int y{0};
+
+  friend auto operator+(WindowPoint const& lhs,
+                        WindowPoint const& rhs) -> WindowPoint {
+    return {lhs.x + rhs.x, lhs.y + rhs.y};
+  }
+
+  friend auto operator-(WindowPoint const& lhs,
+                        WindowPoint const& rhs) -> WindowPoint {
+    return {lhs.x - rhs.x, lhs.y - rhs.y};
+  }
+
+  friend bool operator==(WindowPoint const& lhs, WindowPoint const& rhs) {
+    return lhs.x == rhs.x && lhs.y == rhs.y;
+  }
+};
+
+// A size (width, height) in 2D space.
+struct WindowSize {
+  int width{0};
+  int height{0};
+
+  explicit operator WindowPoint() const { return {width, height}; }
+
+  friend bool operator==(WindowSize const& lhs, WindowSize const& rhs) {
+    return lhs.width == rhs.width && lhs.height == rhs.height;
+  }
+};
+
+// A rectangular area defined by a top-left point and size.
+struct WindowRectangle {
+  WindowPoint top_left;
+  WindowSize size;
+
+  // Checks if this rectangle fully contains |rect|.
+  // Note: An empty rectangle can still contain other empty rectangles,
+  // which are treated as points or lines of thickness zero
+  auto contains(WindowRectangle const& rect) const -> bool {
+    return rect.top_left.x >= top_left.x &&
+           rect.top_left.x + rect.size.width <= top_left.x + size.width &&
+           rect.top_left.y >= top_left.y &&
+           rect.top_left.y + rect.size.height <= top_left.y + size.height;
+  }
+
+  friend bool operator==(WindowRectangle const& lhs,
+                         WindowRectangle const& rhs) {
+    return lhs.top_left == rhs.top_left && lhs.size == rhs.size;
+  }
+};
+
+// Defines how a child window should be positioned relative to its parent.
+struct WindowPositioner {
+  // Allowed anchor positions.
+  enum class Anchor {
+    center,        // Center.
+    top,           // Top, centered horizontally.
+    bottom,        // Bottom, centered horizontally.
+    left,          // Left, centered vertically.
+    right,         // Right, centered vertically.
+    top_left,      // Top-left corner.
+    bottom_left,   // Bottom-left corner.
+    top_right,     // Top-right corner.
+    bottom_right,  // Bottom-right corner.
+  };
+
+  // Specifies how a window should be adjusted if it doesn't fit the placement
+  // bounds. In order of precedence:
+  // 1. 'flip_{x|y|any}': reverse the anchor points and offset along an axis.
+  // 2. 'slide_{x|y|any}': adjust the offset along an axis.
+  // 3. 'resize_{x|y|any}': adjust the window size along an axis.
+  enum class ConstraintAdjustment {
+    none = 0,                          // No adjustment.
+    slide_x = 1 << 0,                  // Slide horizontally to fit.
+    slide_y = 1 << 1,                  // Slide vertically to fit.
+    flip_x = 1 << 2,                   // Flip horizontally to fit.
+    flip_y = 1 << 3,                   // Flip vertically to fit.
+    resize_x = 1 << 4,                 // Resize horizontally to fit.
+    resize_y = 1 << 5,                 // Resize vertically to fit.
+    flip_any = flip_x | flip_y,        // Flip in any direction to fit.
+    slide_any = slide_x | slide_y,     // Slide in any direction to fit.
+    resize_any = resize_x | resize_y,  // Resize in any direction to fit.
+  };
+
+  // The reference anchor rectangle relative to the client rectangle of the
+  // parent window. If nullopt, the anchor rectangle is assumed to be the window
+  // rectangle.
+  std::optional<WindowRectangle> anchor_rect;
+  // Specifies which anchor of the parent window to align to.
+  Anchor parent_anchor{Anchor::center};
+  // Specifies which anchor of the child window to align with the parent.
+  Anchor child_anchor{Anchor::center};
+  // Offset relative to the position of the anchor on the anchor rectangle and
+  // the anchor on the child.
+  WindowPoint offset;
+  // The adjustments to apply if the window doesn't fit the available space.
+  // The order of precedence is: 1) Flip, 2) Slide, 3) Resize.
+  ConstraintAdjustment constraint_adjustment{ConstraintAdjustment::none};
+};
+
+// Types of windows.
+enum class WindowArchetype {
+  // Regular top-level window.
+  regular,
+  // A window that is on a layer above regular windows and is not dockable.
+  floating_regular,
+  // Dialog window.
+  dialog,
+  // Satellite window attached to a regular, floating_regular or dialog window.
+  satellite,
+  // Popup.
+  popup,
+  // Tooltip.
+  tip,
+};
+
+// Window metadata returned as the result of creating a Flutter window.
+struct WindowMetadata {
+  // The ID of the view used for this window, which is unique to each window.
+  FlutterViewId view_id{0};
+  // The type of the window (e.g., regular, dialog, popup, etc).
+  WindowArchetype archetype{WindowArchetype::regular};
+  // Size of the created window, in logical coordinates.
+  WindowSize size;
+  // The ID of the view used by the parent window. If not set, the window is
+  // assumed a top-level window.
+  std::optional<FlutterViewId> parent_id;
+};
+
+}  // namespace flutter
+
+#endif  // FLUTTER_SHELL_PLATFORM_COMMON_CLIENT_WRAPPER_INCLUDE_FLUTTER_WINDOWING_H_

shell/platform/windows/client_wrapper/BUILD.gn

@@ -11,12 +11,19 @@ _wrapper_includes = [
   "include/flutter/flutter_engine.h",
   "include/flutter/flutter_view_controller.h",
   "include/flutter/flutter_view.h",
+  "include/flutter/flutter_win32_window.h",
+  "include/flutter/flutter_window_controller.h",
   "include/flutter/plugin_registrar_windows.h",
+  "include/flutter/win32_window.h",
+  "include/flutter/win32_wrapper.h",
 ]
 
 _wrapper_sources = [
   "flutter_engine.cc",
   "flutter_view_controller.cc",
+  "flutter_win32_window.cc",
+  "flutter_window_controller.cc",
+  "win32_window.cc",
 ]
 
 # This code will be merged into .../common/client_wrapper for client use,
@@ -40,6 +47,8 @@ source_set("client_wrapper_windows") {
     "//flutter/shell/platform/windows:flutter_windows_headers",
   ]
 
+  libs = [ "dwmapi.lib" ]
+
   configs +=
       [ "//flutter/shell/platform/common:desktop_library_implementation" ]
 
@@ -79,6 +88,7 @@ executable("client_wrapper_windows_unittests") {
     "flutter_engine_unittests.cc",
     "flutter_view_controller_unittests.cc",
     "flutter_view_unittests.cc",
+    "flutter_window_controller_unittests.cc",
     "plugin_registrar_windows_unittests.cc",
   ]
 
@@ -89,6 +99,7 @@ executable("client_wrapper_windows_unittests") {
     ":client_wrapper_library_stubs_windows",
     ":client_wrapper_windows",
     ":client_wrapper_windows_fixtures",
+    "//flutter/shell/platform/common/client_wrapper",
     "//flutter/shell/platform/common/client_wrapper:client_wrapper_library_stubs",
     "//flutter/testing",
 
@@ -110,6 +121,9 @@ client_wrapper_file_archive_list = [
 win_client_wrapper_file_archive_list = [
   "flutter_engine.cc",
   "flutter_view_controller.cc",
+  "flutter_win32_window.cc",
+  "flutter_window_controller.cc",
+  "win32_window.cc",
 ]
 
 zip_bundle("client_wrapper_archive") {

shell/platform/windows/client_wrapper/flutter_engine.cc

@@ -63,7 +63,7 @@ bool FlutterEngine::Run(const char* entry_point) {
 }
 
 void FlutterEngine::ShutDown() {
-  if (engine_ && owns_engine_) {
+  if (engine_) {
     FlutterDesktopEngineDestroy(engine_);
   }
   engine_ = nullptr;
@@ -113,8 +113,7 @@ std::optional<LRESULT> FlutterEngine::ProcessExternalWindowMessage(
   return std::nullopt;
 }
 
-FlutterDesktopEngineRef FlutterEngine::RelinquishEngine() {
-  owns_engine_ = false;
+FlutterDesktopEngineRef FlutterEngine::engine() const {
   return engine_;
 }
 

shell/platform/windows/client_wrapper/flutter_view_controller.cc

@@ -11,10 +11,22 @@ namespace flutter {
 
 FlutterViewController::FlutterViewController(int width,
                                              int height,
-                                             const DartProject& project) {
-  engine_ = std::make_shared<FlutterEngine>(project);
-  controller_ = FlutterDesktopViewControllerCreate(width, height,
-                                                   engine_->RelinquishEngine());
+                                             const DartProject& project)
+    : FlutterViewController(width,
+                            height,
+                            std::make_shared<FlutterEngine>(project)) {}
+
+FlutterViewController::FlutterViewController(
+    int width,
+    int height,
+    std::shared_ptr<FlutterEngine> engine) {
+  FlutterDesktopViewControllerProperties properties = {};
+  properties.width = width;
+  properties.height = height;
+
+  engine_ = std::move(engine);
+  controller_ =
+      FlutterDesktopEngineCreateViewController(engine_->engine(), &properties);
   if (!controller_) {
     std::cerr << "Failed to create view controller." << std::endl;
     return;

shell/platform/windows/client_wrapper/flutter_view_controller_unittests.cc

@@ -17,10 +17,8 @@ namespace {
 class TestWindowsApi : public testing::StubFlutterWindowsApi {
  public:
   // |flutter::testing::StubFlutterWindowsApi|
-  FlutterDesktopViewControllerRef ViewControllerCreate(
-      int width,
-      int height,
-      FlutterDesktopEngineRef engine) override {
+  FlutterDesktopViewControllerRef EngineCreateViewController(
+      const FlutterDesktopViewControllerProperties* properties) override {
     return reinterpret_cast<FlutterDesktopViewControllerRef>(2);
   }
 
@@ -63,11 +61,13 @@ TEST(FlutterViewControllerTest, CreateDestroy) {
   testing::ScopedStubFlutterWindowsApi scoped_api_stub(
       std::make_unique<TestWindowsApi>());
   auto test_api = static_cast<TestWindowsApi*>(scoped_api_stub.stub());
+
+  // Create and destroy a view controller.
+  // This should also create and destroy an engine.
   { FlutterViewController controller(100, 100, project); }
+
   EXPECT_TRUE(test_api->view_controller_destroyed());
-  // Per the C API, once a view controller has taken ownership of an engine
-  // the engine destruction method should not be called.
-  EXPECT_FALSE(test_api->engine_destroyed());
+  EXPECT_TRUE(test_api->engine_destroyed());
 }
 
 TEST(FlutterViewControllerTest, GetViewId) {