better handling of very slow computers

git-svn-id: svn+ssh://svn.code.sf.net/p/supertuxkart/code/trunk/supertuxkart@1827 178a84e3-b1eb-0310-8ba1-8eac791a3b58

src/game_manager.cpp

@@ -75,7 +75,12 @@ void GameManager::run()
         {
             m_curr_time = SDL_GetTicks();
             dt =(float)(m_curr_time - m_prev_time);
-
+            
+            // don't allow the game to run slower than a certain amount.
+            // when the computer can't keep it up, slow down the shown time instead
+            static const float max_elapsed_time = 3.0f*1.0f/60.0f*1000.0f; /* time 3 internal substeps take */
+            if(dt > max_elapsed_time) dt=max_elapsed_time;
+                                               
             //This avoid wasting CPU cycles
             //1000 miliseconds / 125 frames = 125 miliseconds per frame
             if( dt < 8.0f)

src/physics.cpp

@@ -95,7 +95,7 @@ void Physics::update(float dt)
 
     // Maximum of three substeps. This will work for framerate down to
     // 20 FPS (bullet default frequency is 60 HZ).
-    m_dynamics_world->stepSimulation(dt, 20);
+    m_dynamics_world->stepSimulation(dt, 3);
 
     // Now handle the actual collision. Note: rockets can not be removed
     // inside of this loop, since the same rocket might hit more than one