Implement an EGL resource context for the Linux shell. (#18918)

Fixes https://github.com/flutter/flutter/issues/54855

shell/platform/linux/fl_engine.cc

@@ -108,6 +108,15 @@ static bool fl_engine_gl_present(void* user_data) {
   return result;
 }
 
+static bool fl_engine_gl_make_resource_current(void* user_data) {
+  FlEngine* self = static_cast<FlEngine*>(user_data);
+  g_autoptr(GError) error = nullptr;
+  gboolean result = fl_renderer_make_resource_current(self->renderer, &error);
+  if (!result)
+    g_warning("%s", error->message);
+  return result;
+}
+
 // Called by the engine to determine if it is on the GTK thread.
 static bool fl_engine_runs_task_on_current_thread(void* user_data) {
   FlEngine* self = static_cast<FlEngine*>(user_data);
@@ -222,6 +231,7 @@ gboolean fl_engine_start(FlEngine* self, GError** error) {
   config.open_gl.clear_current = fl_engine_gl_clear_current;
   config.open_gl.fbo_callback = fl_engine_gl_get_fbo;
   config.open_gl.present = fl_engine_gl_present;
+  config.open_gl.make_resource_current = fl_engine_gl_make_resource_current;
 
   FlutterTaskRunnerDescription platform_task_runner = {};
   platform_task_runner.struct_size = sizeof(FlutterTaskRunnerDescription);

shell/platform/linux/fl_renderer.cc

@@ -12,6 +12,9 @@ typedef struct {
   EGLDisplay egl_display;
   EGLSurface egl_surface;
   EGLContext egl_context;
+
+  EGLSurface resource_surface;
+  EGLContext resource_context;
 } FlRendererPrivate;
 
 G_DEFINE_TYPE_WITH_PRIVATE(FlRenderer, fl_renderer, G_TYPE_OBJECT)
@@ -55,18 +58,38 @@ static const gchar* get_egl_error() {
   }
 }
 
+// Creates a resource surface.
+static void create_resource_surface(FlRenderer* self, EGLConfig config) {
+  FlRendererPrivate* priv =
+      static_cast<FlRendererPrivate*>(fl_renderer_get_instance_private(self));
+
+  EGLint context_attributes[] = {EGL_CONTEXT_CLIENT_VERSION, 2, EGL_NONE};
+  const EGLint resource_context_attribs[] = {EGL_WIDTH, 1, EGL_HEIGHT, 1,
+                                             EGL_NONE};
+  priv->resource_surface = eglCreatePbufferSurface(priv->egl_display, config,
+                                                   resource_context_attribs);
+  if (priv->resource_surface != nullptr) {
+    g_warning("Failed to create EGL resource surface: %s", get_egl_error());
+    return;
+  }
+
+  priv->resource_context = eglCreateContext(
+      priv->egl_display, config, priv->egl_context, context_attributes);
+  if (priv->resource_context == nullptr)
+    g_warning("Failed to create EGL resource context: %s", get_egl_error());
+}
+
 // Default implementation for the start virtual method.
 // Provided so subclasses can chain up to here.
 static gboolean fl_renderer_real_start(FlRenderer* self, GError** error) {
   FlRendererPrivate* priv =
       static_cast<FlRendererPrivate*>(fl_renderer_get_instance_private(self));
 
-  // Note the use of EGL_DEFAULT_DISPLAY rather than sharing an existing display
-  // connection (e.g. an X11 connection from GTK). This is because this EGL
-  // display is going to be accessed by a thread from Flutter. In the case
-  // of GTK/X11 the display connection is not thread safe and this would cause
-  // a crash.
-  //
+  // Note the use of EGL_DEFAULT_DISPLAY rather than sharing an existing
+  // display connection (e.g. an X11 connection from GTK). This is because
+  // this EGL display is going to be accessed by a thread from Flutter. In the
+  // case of GTK/X11 the display connection is not thread safe and this would
+  // cause a crash.
   priv->egl_display = eglGetDisplay(EGL_DEFAULT_DISPLAY);
 
   if (!eglInitialize(priv->egl_display, nullptr, nullptr)) {
@@ -120,6 +143,9 @@ static gboolean fl_renderer_real_start(FlRenderer* self, GError** error) {
                 "Failed to create EGL context: %s", get_egl_error());
     return FALSE;
   }
+
+  create_resource_surface(self, egl_config);
+
   EGLint value;
   eglQueryContext(priv->egl_display, priv->egl_context,
                   EGL_CONTEXT_CLIENT_VERSION, &value);
@@ -155,6 +181,23 @@ gboolean fl_renderer_make_current(FlRenderer* self, GError** error) {
   return TRUE;
 }
 
+gboolean fl_renderer_make_resource_current(FlRenderer* self, GError** error) {
+  FlRendererPrivate* priv =
+      static_cast<FlRendererPrivate*>(fl_renderer_get_instance_private(self));
+
+  if (priv->resource_surface == nullptr || priv->resource_context == nullptr)
+    return FALSE;
+
+  if (!eglMakeCurrent(priv->egl_display, priv->resource_surface,
+                      priv->resource_surface, priv->resource_context)) {
+    g_set_error(error, fl_renderer_error_quark(), FL_RENDERER_ERROR_FAILED,
+                "Failed to make EGL context current: %s", get_egl_error());
+    return FALSE;
+  }
+
+  return TRUE;
+}
+
 gboolean fl_renderer_clear_current(FlRenderer* self, GError** error) {
   FlRendererPrivate* priv =
       static_cast<FlRendererPrivate*>(fl_renderer_get_instance_private(self));

shell/platform/linux/fl_renderer.h

@@ -80,6 +80,19 @@ void* fl_renderer_get_proc_address(FlRenderer* renderer, const char* name);
  */
 gboolean fl_renderer_make_current(FlRenderer* renderer, GError** error);
 
+/**
+ * fl_renderer_make_resource_current:
+ * @renderer: an #FlRenderer.
+ * @error: (allow-none): #GError location to store the error occurring, or %NULL
+ * to ignore.
+ *
+ * Makes the resource rendering context current.
+ *
+ * Returns %TRUE if successful.
+ */
+gboolean fl_renderer_make_resource_current(FlRenderer* renderer,
+                                           GError** error);
+
 /**
  * fl_renderer_clear_current:
  * @renderer: an #FlRenderer.

shell/platform/linux/testing/mock_egl.cc

@@ -23,6 +23,12 @@ EGLContext eglCreateContext(EGLDisplay dpy,
   return nullptr;
 }
 
+EGLSurface eglCreatePbufferSurface(EGLDisplay dpy,
+                                   EGLConfig config,
+                                   const EGLint* attrib_list) {
+  return nullptr;
+}
+
 EGLSurface eglCreateWindowSurface(EGLDisplay dpy,
                                   EGLConfig config,
                                   EGLNativeWindowType win,