Fix terrain derived data update (bug 534, bug 544)

apps/openmw/mwrender/terrain.cpp

@@ -3,6 +3,7 @@
 #include <OgreTerrain.h>
 #include <OgreTerrainGroup.h>
 #include <OgreHardwarePixelBuffer.h>
+#include <OgreRoot.h>
 
 #include "../mwworld/esmstore.hpp"
 
@@ -151,6 +152,16 @@ namespace MWRender
 
                     mTerrainGroup.loadTerrain(terrainX, terrainY, true);
 
+                    // when loading from a heightmap, Ogre::Terrain does not update the derived data (normal map, LOD)
+                    // synchronously, even if we supply synchronous = true parameter to loadTerrain.
+                    // the following to be the only way to make sure derived data is ready when rendering the next frame.
+                    while (mTerrainGroup.isDerivedDataUpdateInProgress())
+                    {
+                       // we need to wait for this to finish
+                       OGRE_THREAD_SLEEP(5);
+                       Root::getSingleton().getWorkQueue()->processResponses();
+                    }
+
                     Terrain* terrain = mTerrainGroup.getTerrain(terrainX, terrainY);
                     initTerrainBlendMaps(terrain,
                                          cellX, cellY,