Add Metal support to MinimalScene and Qt Application

src/Application.cc

@@ -89,6 +89,29 @@ Application::Application(int &_argc, char **_argv, const WindowType _type)
 {
   igndbg << "Initializing application." << std::endl;
 
+#if __APPLE__
+  // Use the Metal graphics API on macOS.
+  igndbg << "Qt using Metal graphics interface" << std::endl;
+  QQuickWindow::setSceneGraphBackend(QSGRendererInterface::MetalRhi);
+
+  // TODO(srmainwaring): implement facility for overriding the default
+  //    graphics API in macOS, in which case there are restrictions on
+  //    the version of OpenGL used.
+  //
+  // macOS only supports OpenGL <= 4.1.
+  // This must be called before the main window is shown.
+  // QSurfaceFormat format(QSurfaceFormat::DeprecatedFunctions);
+  // format.setDepthBufferSize(24);
+  // format.setStencilBufferSize(8);
+  // format.setVersion(4, 1);
+  // format.setProfile(QSurfaceFormat::CoreProfile);
+  // format.setRenderableType(QSurfaceFormat::OpenGL);
+  // QSurfaceFormat::setDefaultFormat(format);
+#else
+  // Otherwise use OpenGL
+  igndbg << "Qt using OpenGL graphics interface" << std::endl;
+#endif
+
   // Configure console
   common::Console::SetPrefix("[GUI] ");
 

src/plugins/minimal_scene/CMakeLists.txt

@@ -1,9 +1,40 @@
+set(SOURCES
+  MinimalScene.cc
+  MinimalSceneRhi.cc
+  MinimalSceneRhiOpenGL.cc
+)
+
+set(PROJECT_LINK_LIBS "")
+
+# Objective-C sources for macOS
+if (APPLE)
+  set(SOURCES
+    ${SOURCES}
+    MinimalSceneRhiMetal.mm
+  )
+
+  set(PROJECT_LINK_LIBS
+    "-framework AppKit"
+    "-framework Metal"
+  )
+endif()
+
 ign_gui_add_plugin(MinimalScene
   SOURCES
-    MinimalScene.cc
+    ${SOURCES}
   QT_HEADERS
     MinimalScene.hh
   PUBLIC_LINK_LIBS
    ignition-rendering${IGN_RENDERING_VER}::ignition-rendering${IGN_RENDERING_VER}
+   ${PROJECT_LINK_LIBS}
 )
 
+# Enable ARC on selected source files
+if (APPLE)
+  set_source_files_properties(
+      MinimalSceneRhiMetal.mm
+      PROPERTIES
+      COMPILE_FLAGS
+          "-fobjc-arc"
+  )
+endif()