Add support for headless mode (#19038)

Author: robert-ancell

ci/licenses_golden/licenses_flutter

@@ -1242,6 +1242,8 @@ FILE: ../../../flutter/shell/platform/linux/fl_plugin_registrar_private.h
 FILE: ../../../flutter/shell/platform/linux/fl_plugin_registry.cc
 FILE: ../../../flutter/shell/platform/linux/fl_renderer.cc
 FILE: ../../../flutter/shell/platform/linux/fl_renderer.h
+FILE: ../../../flutter/shell/platform/linux/fl_renderer_headless.cc
+FILE: ../../../flutter/shell/platform/linux/fl_renderer_headless.h
 FILE: ../../../flutter/shell/platform/linux/fl_renderer_x11.cc
 FILE: ../../../flutter/shell/platform/linux/fl_renderer_x11.h
 FILE: ../../../flutter/shell/platform/linux/fl_standard_message_codec.cc

shell/platform/linux/BUILD.gn

@@ -94,6 +94,7 @@ source_set("flutter_linux_sources") {
     "fl_plugin_registrar.cc",
     "fl_plugin_registry.cc",
     "fl_renderer.cc",
+    "fl_renderer_headless.cc",
     "fl_renderer_x11.cc",
     "fl_standard_message_codec.cc",
     "fl_standard_method_codec.cc",

shell/platform/linux/fl_engine.cc

@@ -6,7 +6,10 @@
 #include "flutter/shell/platform/linux/fl_engine_private.h"
 
 #include "flutter/shell/platform/linux/fl_binary_messenger_private.h"
+#include "flutter/shell/platform/linux/fl_plugin_registrar_private.h"
 #include "flutter/shell/platform/linux/fl_renderer.h"
+#include "flutter/shell/platform/linux/fl_renderer_headless.h"
+#include "flutter/shell/platform/linux/public/flutter_linux/fl_plugin_registry.h"
 
 #include <gmodule.h>
 
@@ -35,7 +38,15 @@ struct _FlEngine {
 
 G_DEFINE_QUARK(fl_engine_error_quark, fl_engine_error)
 
-G_DEFINE_TYPE(FlEngine, fl_engine, G_TYPE_OBJECT)
+static void fl_engine_plugin_registry_iface_init(
+    FlPluginRegistryInterface* iface);
+
+G_DEFINE_TYPE_WITH_CODE(
+    FlEngine,
+    fl_engine,
+    G_TYPE_OBJECT,
+    G_IMPLEMENT_INTERFACE(fl_plugin_registry_get_type(),
+                          fl_engine_plugin_registry_iface_init))
 
 // Subclass of GSource that integrates Flutter tasks into the GLib main loop.
 typedef struct {
@@ -169,6 +180,20 @@ static void fl_engine_platform_message_response_cb(const uint8_t* data,
                         (GDestroyNotify)g_bytes_unref);
 }
 
+// Implements FlPluginRegistry::get_registrar_for_plugin.
+static FlPluginRegistrar* fl_engine_get_registrar_for_plugin(
+    FlPluginRegistry* registry,
+    const gchar* name) {
+  FlEngine* self = FL_ENGINE(registry);
+
+  return fl_plugin_registrar_new(nullptr, self->binary_messenger);
+}
+
+static void fl_engine_plugin_registry_iface_init(
+    FlPluginRegistryInterface* iface) {
+  iface->get_registrar_for_plugin = fl_engine_get_registrar_for_plugin;
+}
+
 static void fl_engine_dispose(GObject* object) {
   FlEngine* self = FL_ENGINE(object);
 
@@ -210,13 +235,17 @@ FlEngine* fl_engine_new(FlDartProject* project, FlRenderer* renderer) {
   g_return_val_if_fail(FL_IS_DART_PROJECT(project), nullptr);
   g_return_val_if_fail(FL_IS_RENDERER(renderer), nullptr);
 
-  FlEngine* self =
-      static_cast<FlEngine*>(g_object_new(fl_engine_get_type(), nullptr));
-  self->project = static_cast<FlDartProject*>(g_object_ref(project));
-  self->renderer = static_cast<FlRenderer*>(g_object_ref(renderer));
+  FlEngine* self = FL_ENGINE(g_object_new(fl_engine_get_type(), nullptr));
+  self->project = FL_DART_PROJECT(g_object_ref(project));
+  self->renderer = FL_RENDERER(g_object_ref(renderer));
   return self;
 }
 
+G_MODULE_EXPORT FlEngine* fl_engine_new_headless(FlDartProject* project) {
+  g_autoptr(FlRendererHeadless) renderer = fl_renderer_headless_new();
+  return fl_engine_new(project, FL_RENDERER(renderer));
+}
+
 gboolean fl_engine_start(FlEngine* self, GError** error) {
   g_return_val_if_fail(FL_IS_ENGINE(self), FALSE);
 

shell/platform/linux/fl_plugin_registrar.cc

@@ -48,14 +48,15 @@ static void fl_plugin_registrar_init(FlPluginRegistrar* self) {}
 
 FlPluginRegistrar* fl_plugin_registrar_new(FlView* view,
                                            FlBinaryMessenger* messenger) {
-  g_return_val_if_fail(FL_IS_VIEW(view), nullptr);
+  g_return_val_if_fail(view == nullptr || FL_IS_VIEW(view), nullptr);
   g_return_val_if_fail(FL_IS_BINARY_MESSENGER(messenger), nullptr);
 
   FlPluginRegistrar* self = FL_PLUGIN_REGISTRAR(
       g_object_new(fl_plugin_registrar_get_type(), nullptr));
 
   self->view = view;
-  g_object_weak_ref(G_OBJECT(view), view_weak_notify_cb, self);
+  if (view != nullptr)
+    g_object_weak_ref(G_OBJECT(view), view_weak_notify_cb, self);
   self->messenger = FL_BINARY_MESSENGER(g_object_ref(messenger));
 
   return self;

shell/platform/linux/fl_plugin_registrar_private.h

@@ -12,7 +12,8 @@ G_BEGIN_DECLS
 
 /**
  * fl_plugin_registrar_new:
- * @view: the #FlView that is being plugged into.
+ * @view: (allow-none): the #FlView that is being plugged into or %NULL for
+ * headless mode.
  * @messenger: the #FlBinaryMessenger to communicate with.
  *
  * Creates a new #FlPluginRegistrar.

shell/platform/linux/fl_renderer_headless.cc

@@ -0,0 +1,29 @@
+// 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.
+
+#include "fl_renderer_headless.h"
+
+struct _FlRendererHeadless {
+  FlRenderer parent_instance;
+};
+
+G_DEFINE_TYPE(FlRendererHeadless, fl_renderer_headless, fl_renderer_get_type())
+
+static EGLSurface fl_renderer_headless_create_surface(FlRenderer* renderer,
+                                                      EGLDisplay display,
+                                                      EGLConfig config) {
+  return EGL_NO_SURFACE;
+}
+
+static void fl_renderer_headless_class_init(FlRendererHeadlessClass* klass) {
+  FL_RENDERER_CLASS(klass)->create_surface =
+      fl_renderer_headless_create_surface;
+}
+
+static void fl_renderer_headless_init(FlRendererHeadless* self) {}
+
+FlRendererHeadless* fl_renderer_headless_new() {
+  return FL_RENDERER_HEADLESS(
+      g_object_new(fl_renderer_headless_get_type(), nullptr));
+}

shell/platform/linux/fl_renderer_headless.h

@@ -0,0 +1,36 @@
+// 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_LINUX_FL_RENDERER_HEADLESS_H_
+#define FLUTTER_SHELL_PLATFORM_LINUX_FL_RENDERER_HEADLESS_H_
+
+#include "flutter/shell/platform/linux/fl_renderer.h"
+
+G_BEGIN_DECLS
+
+G_DECLARE_FINAL_TYPE(FlRendererHeadless,
+                     fl_renderer_headless,
+                     FL,
+                     RENDERER_HEADLESS,
+                     FlRenderer)
+
+/**
+ * FlRendererHeadless:
+ *
+ * #FlRendererHeadless is an implementation of #FlRenderer that works without a
+ * display.
+ */
+
+/**
+ * fl_renderer_headless_new:
+ *
+ * Creates an object that allows Flutter to operate without a display.
+ *
+ * Returns: a new #FlRendererHeadless.
+ */
+FlRendererHeadless* fl_renderer_headless_new();
+
+G_END_DECLS
+
+#endif  // FLUTTER_SHELL_PLATFORM_LINUX_FL_RENDERER_HEADLESS_H_

shell/platform/linux/public/flutter_linux/fl_engine.h

@@ -24,6 +24,16 @@ G_DECLARE_FINAL_TYPE(FlEngine, fl_engine, FL, ENGINE, GObject)
  * #FlEngine is an object that contains a running Flutter engine.
  */
 
+/**
+ * fl_engine_new_headless:
+ * @project: an #FlDartProject.
+ *
+ * Creates new Flutter engine running in headless mode.
+ *
+ * Returns: a new #FlEngine.
+ */
+FlEngine* fl_engine_new_headless(FlDartProject* project);
+
 /**
  * fl_engine_get_binary_messenger:
  * @engine: an #FlEngine.