qt: Fix black screen when switching between renderers

src/qt/qt_rendererstack.cpp

@@ -237,6 +237,8 @@ RendererStack::switchRenderer(Renderer renderer)
 {
     startblit();
     if (current) {
+        if ((current_vid_api == Renderer::Direct3D9 && renderer != Renderer::Direct3D9)
+        || (current_vid_api != Renderer::Direct3D9 && renderer == Renderer::Direct3D9)) {
             rendererWindow->finalize();
             if (rendererWindow->hasBlitFunc()) {
                 while (directBlitting) {}
@@ -259,6 +261,16 @@ RendererStack::switchRenderer(Renderer renderer)
             });
 
             rendererWindow->hasBlitFunc() ? current.reset() : current.release()->deleteLater();
+        } else {
+            rendererWindow->finalize();
+            removeWidget(current.get());
+            disconnect(this, &RendererStack::blitToRenderer, nullptr, nullptr);
+
+            /* Create new renderer only after previous is destroyed! */
+            connect(current.get(), &QObject::destroyed, [this, renderer](QObject *) { createRenderer(renderer); });
+
+            current.release()->deleteLater();
+        }
     } else {
         createRenderer(renderer);
     }
@@ -267,6 +279,7 @@ RendererStack::switchRenderer(Renderer renderer)
 void
 RendererStack::createRenderer(Renderer renderer)
 {
+    current_vid_api = renderer;
     switch (renderer) {
         default:
         case Renderer::Software:

src/qt/qt_rendererstack.hpp

@@ -47,7 +47,8 @@ public:
         OpenGLES,
         OpenGL3,
         Vulkan,
-        Direct3D9
+        Direct3D9,
+        None = -1
     };
     void switchRenderer(Renderer renderer);
 
@@ -96,6 +97,8 @@ private:
     int isMouseDown = 0;
     int m_monitor_index = 0;
 
+    Renderer current_vid_api = Renderer::None;
+
     std::vector<std::tuple<uint8_t *, std::atomic_flag *>> imagebufs;
 
     RendererCommon          *rendererWindow { nullptr };