Allow the default background color to be changed

shell/platform/linux/fl_renderer.cc

@@ -195,6 +195,9 @@ static void render_with_textures(FlRenderer* self, int width, int height) {
   GLint saved_array_buffer_binding;
   glGetIntegerv(GL_ARRAY_BUFFER_BINDING, &saved_array_buffer_binding);
 
+  glEnable(GL_BLEND);
+  glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);
+
   glUseProgram(priv->program);
 
   for (guint i = 0; i < priv->framebuffers->len; i++) {
@@ -236,6 +239,8 @@ static void render_with_textures(FlRenderer* self, int width, int height) {
     glDeleteBuffers(1, &vertex_buffer);
   }
 
+  glDisable(GL_BLEND);
+
   glBindTexture(GL_TEXTURE_2D, saved_texture_binding);
   glBindVertexArray(saved_vao_binding);
   glBindBuffer(GL_ARRAY_BUFFER, saved_array_buffer_binding);
@@ -443,13 +448,17 @@ void fl_renderer_setup(FlRenderer* self) {
   }
 }
 
-void fl_renderer_render(FlRenderer* self, int width, int height) {
+void fl_renderer_render(FlRenderer* self,
+                        int width,
+                        int height,
+                        const GdkRGBA* background_color) {
   FlRendererPrivate* priv = reinterpret_cast<FlRendererPrivate*>(
       fl_renderer_get_instance_private(self));
 
   g_return_if_fail(FL_IS_RENDERER(self));
 
-  glClearColor(0.0, 0.0, 0.0, 1.0);
+  glClearColor(background_color->red, background_color->green,
+               background_color->blue, background_color->alpha);
   glClear(GL_COLOR_BUFFER_BIT);
 
   if (priv->has_gl_framebuffer_blit) {

shell/platform/linux/fl_renderer.h

@@ -209,10 +209,14 @@ void fl_renderer_setup(FlRenderer* renderer);
  * @renderer: an #FlRenderer.
  * @width: width of the window in pixels.
  * @height: height of the window in pixels.
+ * @background_color: color to use for background.
  *
  * Performs OpenGL commands to render current Flutter view.
  */
-void fl_renderer_render(FlRenderer* renderer, int width, int height);
+void fl_renderer_render(FlRenderer* renderer,
+                        int width,
+                        int height,
+                        const GdkRGBA* background_color);
 
 /**
  * fl_renderer_cleanup:

shell/platform/linux/fl_renderer_test.cc

@@ -12,6 +12,36 @@
 
 #include <epoxy/egl.h>
 
+TEST(FlRendererTest, BackgroundColor) {
+  ::testing::NiceMock<flutter::testing::MockEpoxy> epoxy;
+
+  ON_CALL(epoxy, epoxy_is_desktop_gl).WillByDefault(::testing::Return(true));
+  EXPECT_CALL(epoxy, epoxy_gl_version).WillRepeatedly(::testing::Return(30));
+  ON_CALL(epoxy, glGetString(GL_VENDOR))
+      .WillByDefault(
+          ::testing::Return(reinterpret_cast<const GLubyte*>("Intel")));
+  EXPECT_CALL(epoxy, glClearColor(0.2, 0.3, 0.4, 0.5));
+
+  g_autoptr(FlMockRenderer) renderer = fl_mock_renderer_new();
+  fl_renderer_setup(FL_RENDERER(renderer));
+  fl_renderer_wait_for_frame(FL_RENDERER(renderer), 1024, 1024);
+  FlutterBackingStoreConfig config = {
+      .struct_size = sizeof(FlutterBackingStoreConfig),
+      .size = {.width = 1024, .height = 1024}};
+  FlutterBackingStore backing_store;
+  fl_renderer_create_backing_store(FL_RENDERER(renderer), &config,
+                                   &backing_store);
+  const FlutterLayer layer0 = {.struct_size = sizeof(FlutterLayer),
+                               .type = kFlutterLayerContentTypeBackingStore,
+                               .backing_store = &backing_store,
+                               .size = {.width = 1024, .height = 1024}};
+  const FlutterLayer* layers[] = {&layer0};
+  fl_renderer_present_layers(FL_RENDERER(renderer), 0, layers, 1);
+  GdkRGBA background_color = {
+      .red = 0.2, .green = 0.3, .blue = 0.4, .alpha = 0.5};
+  fl_renderer_render(FL_RENDERER(renderer), 1024, 1024, &background_color);
+}
+
 TEST(FlRendererTest, RestoresGLState) {
   ::testing::NiceMock<flutter::testing::MockEpoxy> epoxy;
 
@@ -44,7 +74,9 @@ TEST(FlRendererTest, RestoresGLState) {
 
   fl_renderer_present_layers(FL_RENDERER(renderer), 0, layers.data(),
                              layers.size());
-  fl_renderer_render(FL_RENDERER(renderer), kWidth, kHeight);
+  GdkRGBA background_color = {
+      .red = 0.0, .green = 0.0, .blue = 0.0, .alpha = 1.0};
+  fl_renderer_render(FL_RENDERER(renderer), kWidth, kHeight, &background_color);
 
   GLuint texture_2d_binding;
   glGetIntegerv(GL_TEXTURE_BINDING_2D,
@@ -82,8 +114,7 @@ TEST(FlRendererTest, BlitFramebuffer) {
 
   EXPECT_CALL(epoxy, glBlitFramebuffer);
 
-  g_autoptr(FlMockRenderer) renderer =
-      fl_mock_renderer_new(&renderer_get_refresh_rate);
+  g_autoptr(FlMockRenderer) renderer = fl_mock_renderer_new();
   fl_renderer_setup(FL_RENDERER(renderer));
   fl_renderer_wait_for_frame(FL_RENDERER(renderer), 1024, 1024);
   FlutterBackingStoreConfig config = {
@@ -98,7 +129,9 @@ TEST(FlRendererTest, BlitFramebuffer) {
                                .size = {.width = 1024, .height = 1024}};
   const FlutterLayer* layers[] = {&layer0};
   fl_renderer_present_layers(FL_RENDERER(renderer), 0, layers, 1);
-  fl_renderer_render(FL_RENDERER(renderer), 1024, 1024);
+  GdkRGBA background_color = {
+      .red = 0.0, .green = 0.0, .blue = 0.0, .alpha = 1.0};
+  fl_renderer_render(FL_RENDERER(renderer), 1024, 1024, &background_color);
 }
 
 TEST(FlRendererTest, BlitFramebufferExtension) {
@@ -116,8 +149,7 @@ TEST(FlRendererTest, BlitFramebufferExtension) {
 
   EXPECT_CALL(epoxy, glBlitFramebuffer);
 
-  g_autoptr(FlMockRenderer) renderer =
-      fl_mock_renderer_new(&renderer_get_refresh_rate);
+  g_autoptr(FlMockRenderer) renderer = fl_mock_renderer_new();
   fl_renderer_setup(FL_RENDERER(renderer));
   fl_renderer_wait_for_frame(FL_RENDERER(renderer), 1024, 1024);
   FlutterBackingStoreConfig config = {
@@ -132,7 +164,9 @@ TEST(FlRendererTest, BlitFramebufferExtension) {
                                .size = {.width = 1024, .height = 1024}};
   const FlutterLayer* layers[] = {&layer0};
   fl_renderer_present_layers(FL_RENDERER(renderer), 0, layers, 1);
-  fl_renderer_render(FL_RENDERER(renderer), 1024, 1024);
+  GdkRGBA background_color = {
+      .red = 0.0, .green = 0.0, .blue = 0.0, .alpha = 1.0};
+  fl_renderer_render(FL_RENDERER(renderer), 1024, 1024, &background_color);
 }
 
 TEST(FlRendererTest, NoBlitFramebuffer) {
@@ -145,8 +179,7 @@ TEST(FlRendererTest, NoBlitFramebuffer) {
   ON_CALL(epoxy, epoxy_is_desktop_gl).WillByDefault(::testing::Return(true));
   EXPECT_CALL(epoxy, epoxy_gl_version).WillRepeatedly(::testing::Return(20));
 
-  g_autoptr(FlMockRenderer) renderer =
-      fl_mock_renderer_new(&renderer_get_refresh_rate);
+  g_autoptr(FlMockRenderer) renderer = fl_mock_renderer_new();
   fl_renderer_setup(FL_RENDERER(renderer));
   fl_renderer_wait_for_frame(FL_RENDERER(renderer), 1024, 1024);
   FlutterBackingStoreConfig config = {
@@ -161,7 +194,9 @@ TEST(FlRendererTest, NoBlitFramebuffer) {
                                .size = {.width = 1024, .height = 1024}};
   const FlutterLayer* layers[] = {&layer0};
   fl_renderer_present_layers(FL_RENDERER(renderer), 0, layers, 1);
-  fl_renderer_render(FL_RENDERER(renderer), 1024, 1024);
+  GdkRGBA background_color = {
+      .red = 0.0, .green = 0.0, .blue = 0.0, .alpha = 1.0};
+  fl_renderer_render(FL_RENDERER(renderer), 1024, 1024, &background_color);
 }
 
 TEST(FlRendererTest, BlitFramebufferNvidia) {
@@ -175,8 +210,7 @@ TEST(FlRendererTest, BlitFramebufferNvidia) {
   ON_CALL(epoxy, epoxy_is_desktop_gl).WillByDefault(::testing::Return(true));
   EXPECT_CALL(epoxy, epoxy_gl_version).WillRepeatedly(::testing::Return(30));
 
-  g_autoptr(FlMockRenderer) renderer =
-      fl_mock_renderer_new(&renderer_get_refresh_rate);
+  g_autoptr(FlMockRenderer) renderer = fl_mock_renderer_new();
   fl_renderer_setup(FL_RENDERER(renderer));
   fl_renderer_wait_for_frame(FL_RENDERER(renderer), 1024, 1024);
   FlutterBackingStoreConfig config = {
@@ -191,5 +225,7 @@ TEST(FlRendererTest, BlitFramebufferNvidia) {
                                .size = {.width = 1024, .height = 1024}};
   const FlutterLayer* layers[] = {&layer0};
   fl_renderer_present_layers(FL_RENDERER(renderer), 0, layers, 1);
-  fl_renderer_render(FL_RENDERER(renderer), 1024, 1024);
+  GdkRGBA background_color = {
+      .red = 0.0, .green = 0.0, .blue = 0.0, .alpha = 1.0};
+  fl_renderer_render(FL_RENDERER(renderer), 1024, 1024, &background_color);
 }

shell/platform/linux/fl_view.cc

@@ -46,6 +46,9 @@ struct _FlView {
   // Rendering output.
   FlRendererGdk* renderer;
 
+  // Background color.
+  GdkRGBA* background_color;
+
   // Pointer button state recorded for sending status updates.
   int64_t button_state;
 
@@ -607,7 +610,7 @@ static gboolean render_cb(FlView* self, GdkGLContext* context) {
   int height = gtk_widget_get_allocated_height(GTK_WIDGET(self->gl_area));
   gint scale_factor = gtk_widget_get_scale_factor(GTK_WIDGET(self->gl_area));
   fl_renderer_render(FL_RENDERER(self->renderer), width * scale_factor,
-                     height * scale_factor);
+                     height * scale_factor, self->background_color);
 
   return TRUE;
 }
@@ -654,6 +657,7 @@ static void fl_view_dispose(GObject* object) {
 
   g_clear_object(&self->engine);
   g_clear_object(&self->renderer);
+  g_clear_pointer(&self->background_color, gdk_rgba_free);
   g_clear_object(&self->window_state_monitor);
   g_clear_object(&self->scrolling_manager);
   g_clear_object(&self->keyboard_handler);
@@ -706,6 +710,10 @@ static void fl_view_init(FlView* self) {
   // https://github.com/flutter/flutter/issues/138178
   self->view_id = flutter::kFlutterImplicitViewId;
 
+  GdkRGBA default_background = {
+      .red = 0.0, .green = 0.0, .blue = 0.0, .alpha = 1.0};
+  self->background_color = gdk_rgba_copy(&default_background);
+
   self->event_box = gtk_event_box_new();
   gtk_widget_set_hexpand(self->event_box, TRUE);
   gtk_widget_set_vexpand(self->event_box, TRUE);
@@ -743,6 +751,7 @@ static void fl_view_init(FlView* self) {
                            self);
 
   self->gl_area = GTK_GL_AREA(gtk_gl_area_new());
+  gtk_gl_area_set_has_alpha(self->gl_area, TRUE);
   gtk_widget_show(GTK_WIDGET(self->gl_area));
   gtk_container_add(GTK_CONTAINER(self->event_box), GTK_WIDGET(self->gl_area));
 
@@ -785,6 +794,13 @@ G_MODULE_EXPORT FlEngine* fl_view_get_engine(FlView* self) {
   return self->engine;
 }
 
+G_MODULE_EXPORT void fl_view_set_background_color(FlView* self,
+                                                  const GdkRGBA* color) {
+  g_return_if_fail(FL_IS_VIEW(self));
+  gdk_rgba_free(self->background_color);
+  self->background_color = gdk_rgba_copy(color);
+}
+
 void fl_view_redraw(FlView* self) {
   g_return_if_fail(FL_IS_VIEW(self));
   gtk_widget_queue_draw(GTK_WIDGET(self->gl_area));

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

@@ -69,6 +69,15 @@ FlView* fl_view_new_for_engine(FlEngine* engine);
  */
 FlEngine* fl_view_get_engine(FlView* view);
 
+/**
+ * fl_view_set_background_color:
+ * @view: an #FlView.
+ * @color: a background color.
+ *
+ * Set the background color for Flutter (defaults to black).
+ */
+void fl_view_set_background_color(FlView* view, const GdkRGBA* color);
+
 G_END_DECLS
 
 #endif  // FLUTTER_SHELL_PLATFORM_LINUX_PUBLIC_FLUTTER_LINUX_FL_VIEW_H_

shell/platform/linux/testing/mock_epoxy.cc

@@ -382,6 +382,10 @@ GLuint _glCreateProgram() {
 
 void _glCompileShader(GLuint shader) {}
 
+void _glClearColor(GLfloat r, GLfloat g, GLfloat b, GLfloat a) {
+  mock->glClearColor(r, g, b, a);
+}
+
 GLuint _glCreateShader(GLenum shaderType) {
   return 0;
 }
@@ -594,6 +598,7 @@ static void library_init() {
   epoxy_glBindTexture = _glBindTexture;
   epoxy_glBlitFramebuffer = _glBlitFramebuffer;
   epoxy_glCompileShader = _glCompileShader;
+  epoxy_glClearColor = _glClearColor;
   epoxy_glCreateProgram = _glCreateProgram;
   epoxy_glCreateShader = _glCreateShader;
   epoxy_glDeleteFramebuffers = _glDeleteFramebuffers;

shell/platform/linux/testing/mock_epoxy.h

@@ -20,6 +20,7 @@ class MockEpoxy {
   MOCK_METHOD(bool, epoxy_has_gl_extension, (const char* extension));
   MOCK_METHOD(bool, epoxy_is_desktop_gl, ());
   MOCK_METHOD(int, epoxy_gl_version, ());
+  MOCK_METHOD(void, glClearColor, (GLfloat r, GLfloat g, GLfloat b, GLfloat a));
   MOCK_METHOD(void,
               glBlitFramebuffer,
               (GLint srcX0,