Bug #416: Workaround for page flipping problem

apps/openmw/mwgui/loadingscreen.cpp

@@ -72,6 +72,10 @@ namespace MWGui
 
     void LoadingScreen::loadingOn()
     {
+        // Early-out if already on
+        if (mRectangle->getVisible())
+            return;
+
         // Temporarily turn off VSync, we want to do actual loading rather than waiting for the screen to sync.
         // Threaded loading would be even better, of course - especially because some drivers force VSync to on and we can't change it.
         // In Ogre 1.8, the swapBuffers argument is useless and setVSyncEnabled is bugged with GLX, nothing we can do :/
@@ -80,6 +84,15 @@ namespace MWGui
         mWindow->setVSyncEnabled(false);
         #endif
 
+        if (!mFirstLoad)
+        {
+            // When the loading screen is updated, we will disable render target clearing and only draw the loading bar itself.
+            // But if using page flipping, this can cause jitteriness as it will alternate between the last two rendered frames.
+            // Even though we attempt to disable vsync above, this may not work if it's forced on the driver level.
+            // Therefore render the same frame twice before activating the loading bar.
+            mWindow->update();
+        }
+
         setVisible(true);
 
         if (mFirstLoad)

apps/openmw/mwworld/scene.cpp

@@ -214,12 +214,13 @@ namespace MWWorld
 
     void Scene::changeCell (int X, int Y, const ESM::Position& position, bool adjustPlayerPos)
     {
-        mRendering.enableTerrain(true);
         Nif::NIFFile::CacheLock cachelock;
 
         Loading::Listener* loadingListener = MWBase::Environment::get().getWindowManager()->getLoadingScreen();
         Loading::ScopedLoad load(loadingListener);
 
+        mRendering.enableTerrain(true);
+
         std::string loadingExteriorText = "#{sLoadingMessage3}";
         loadingListener->setLabel(loadingExteriorText);
 
@@ -364,11 +365,11 @@ namespace MWWorld
         Nif::NIFFile::CacheLock lock;
         MWBase::Environment::get().getWorld ()->getFader ()->fadeOut(0.5);
 
-        mRendering.enableTerrain(false);
-
         Loading::Listener* loadingListener = MWBase::Environment::get().getWindowManager()->getLoadingScreen();
         Loading::ScopedLoad load(loadingListener);
 
+        mRendering.enableTerrain(false);
+
         std::string loadingInteriorText = "#{sLoadingMessage2}";
         loadingListener->setLabel(loadingInteriorText);