From 964a5682905f0f07a2fd5a45cf6ccdc49ac983ea Mon Sep 17 00:00:00 2001
From: "Matias N. Goldberg" <dark_sylinc@yahoo.com.ar>
Date: Sat, 24 Sep 2022 17:50:02 -0300
Subject: [PATCH] Add CLI to switch to Vulkan/Metal

Signed-off-by: Matias N. Goldberg <dark_sylinc@yahoo.com.ar>
---
 include/gz/gui/Application.hh |  5 +++-
 src/Application.cc            | 56 ++++++++++++++++++++++++++++-------
 2 files changed, 50 insertions(+), 11 deletions(-)

diff --git a/include/gz/gui/Application.hh b/include/gz/gui/Application.hh
index c5e73f9a5..edabeee15 100644
--- a/include/gz/gui/Application.hh
+++ b/include/gz/gui/Application.hh
@@ -70,8 +70,11 @@ namespace gz
       /// \param[in] _argc Argument count.
       /// \param[in] _argv Argument values.
       /// \param[in] _type Window type, by default it's a main window.
+      /// \param[in] _renderEngineGuiApiBackend --render-engine-gui-api-backend
+      /// option
       public: Application(int &_argc, char **_argv,
-          const WindowType _type = WindowType::kMainWindow);
+          const WindowType _type = WindowType::kMainWindow,
+          const char *_renderEngineGuiApiBackend = nullptr);
 
       /// \brief Destructor
       public: virtual ~Application();
diff --git a/src/Application.cc b/src/Application.cc
index 1c5265daa..3568d5ab3 100644
--- a/src/Application.cc
+++ b/src/Application.cc
@@ -89,9 +89,18 @@ namespace gz
 using namespace gz;
 using namespace gui;
 
+enum class GZ_COMMON_HIDDEN AvailableAPIs
+{
+  OpenGL,
+  Vulkan,
+  Metal
+};
+
 /////////////////////////////////////////////////
-Application::Application(int &_argc, char **_argv, const WindowType _type)
-  : QApplication(_argc, _argv), dataPtr(new ApplicationPrivate)
+Application::Application(int &_argc, char **_argv, const WindowType _type,
+                         const char *_renderEngineGuiApiBackend) :
+  QApplication(_argc, _argv),
+  dataPtr(new ApplicationPrivate)
 {
   gzdbg << "Initializing application." << std::endl;
 
@@ -99,10 +108,29 @@ Application::Application(int &_argc, char **_argv, const WindowType _type)
   this->setOrganizationDomain("gazebosim.org");
   this->setApplicationName("Gazebo GUI");
 
-#if __APPLE__
-  // Use the Metal graphics API on macOS.
-  gzdbg << "Qt using Metal graphics interface" << std::endl;
-  QQuickWindow::setSceneGraphBackend(QSGRendererInterface::MetalRhi);
+#ifdef __APPLE__
+  AvailableAPIs api = AvailableAPIs::Metal;
+#else
+  AvailableAPIs api = AvailableAPIs::OpenGL;
+#endif
+  if (_renderEngineGuiApiBackend)
+  {
+    const std::string renderEngineGuiApiBackend = _renderEngineGuiApiBackend;
+    if (renderEngineGuiApiBackend == "vulkan")
+      api = AvailableAPIs::Vulkan;
+#ifdef __APPLE__
+    if (renderEngineGuiApiBackend == "metal")
+      api = AvailableAPIs::Metal;
+#endif
+  }
+
+#ifdef __APPLE__
+  if (api == AvailableAPIs::Metal)
+  {
+    // Use the Metal graphics API on macOS.
+    gzdbg << "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
@@ -120,9 +148,7 @@ Application::Application(int &_argc, char **_argv, const WindowType _type)
 #else
   // Otherwise use OpenGL (or Vulkan when supported and requested)
 
-  const bool useVulkan = true;  // TODO(anyone)
-
-  if (useVulkan)
+  if (api == AvailableAPIs::Vulkan)
   {
     gzdbg << "Qt using Vulkan graphics interface" << std::endl;
 
@@ -180,10 +206,20 @@ Application::Application(int &_argc, char **_argv, const WindowType _type)
     }
     else
     {
-      if (useVulkan)
+      switch (api)
       {
+      case AvailableAPIs::OpenGL:
+        this->dataPtr->mainWin->setProperty("renderEngineBackendApiName",
+                                            "opengl");
+        break;
+      case AvailableAPIs::Vulkan:
         this->dataPtr->mainWin->setProperty("renderEngineBackendApiName",
                                             "vulkan");
+        break;
+      case AvailableAPIs::Metal:
+        this->dataPtr->mainWin->setProperty("renderEngineBackendApiName",
+                                            "metal");
+        break;
       }
     }
   }