Allow embedder clients to provide a resource context (flutter/engine#4588)

* Allow embedder clients to provide a resource context. Closes flutter/flutter#14263.

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

@@ -125,6 +125,15 @@ FlutterResult FlutterEngineRun(size_t version,
     };
   }
 
+  const FlutterOpenGLRendererConfig* open_gl_config = &config->open_gl;
+  std::function<bool()> make_resource_current_callback = nullptr;
+  if (SAFE_ACCESS(open_gl_config, make_resource_current, nullptr) != nullptr) {
+    make_resource_current_callback =
+        [ ptr = config->open_gl.make_resource_current, user_data ]() {
+      return ptr(user_data);
+    };
+  }
+
   std::string icu_data_path;
   if (SAFE_ACCESS(args, icu_data_path, nullptr) != nullptr) {
     icu_data_path = SAFE_ACCESS(args, icu_data_path, nullptr);
@@ -154,6 +163,7 @@ FlutterResult FlutterEngineRun(size_t version,
       .gl_present_callback = present,
       .gl_fbo_callback = fbo_callback,
       .platform_message_response_callback = platform_message_response_callback,
+      .gl_make_resource_current_callback = make_resource_current_callback,
   };
 
   auto platform_view = std::make_shared<shell::PlatformViewEmbedder>(table);

engine/src/flutter/shell/platform/embedder/embedder.h

@@ -41,6 +41,7 @@ typedef struct {
   BoolCallback clear_current;
   BoolCallback present;
   UIntCallback fbo_callback;
+  BoolCallback make_resource_current;
 } FlutterOpenGLRendererConfig;
 
 typedef struct {

engine/src/flutter/shell/platform/embedder/platform_view_embedder.cc

@@ -34,11 +34,17 @@ intptr_t PlatformViewEmbedder::GLContextFBO() const {
 void PlatformViewEmbedder::Attach() {
   CreateEngine();
   NotifyCreated(std::make_unique<shell::GPUSurfaceGL>(this));
+
+  if (dispatch_table_.gl_make_resource_current_callback != nullptr) {
+    SetupResourceContextOnIOThread();
+  }
 }
 
 bool PlatformViewEmbedder::ResourceContextMakeCurrent() {
-  // Unsupported.
-  return false;
+  if (dispatch_table_.gl_make_resource_current_callback == nullptr) {
+    return false;
+  }
+  return dispatch_table_.gl_make_resource_current_callback();
 }
 
 void PlatformViewEmbedder::RunFromSource(const std::string& assets_directory,

engine/src/flutter/shell/platform/embedder/platform_view_embedder.h

@@ -22,7 +22,8 @@ class PlatformViewEmbedder : public PlatformView, public GPUSurfaceGLDelegate {
     std::function<bool(void)> gl_present_callback;        // required
     std::function<intptr_t(void)> gl_fbo_callback;        // required
     PlatformMessageResponseCallback
-        platform_message_response_callback;  // optional
+        platform_message_response_callback;                       // optional
+    std::function<bool(void)> gl_make_resource_current_callback;  // optional
   };
 
   PlatformViewEmbedder(DispatchTable dispatch_table);