Always use real dt for cutscenes.

It fixes #3213

src/main_loop.cpp

@@ -72,6 +72,7 @@ MainLoop::MainLoop(unsigned parent_pid)
     m_curr_time       = 0;
     m_prev_time       = 0;
     m_throttle_fps    = true;
+    m_allow_large_dt  = false;
     m_frame_before_loading_world = false;
 #ifdef WIN32
     if (parent_pid != 0)
@@ -159,8 +160,8 @@ float MainLoop::getLimitedDt()
         // when the computer can't keep it up, slow down the shown time instead
         // But this can not be done in networking, otherwise the game time on
         // client and server will not be in synch anymore
-        if (!NetworkConfig::get()->isNetworking() ||
-           !World::getWorld())
+        if ((!NetworkConfig::get()->isNetworking() || !World::getWorld()) &&
+            !m_allow_large_dt)
         {
             /* time 3 internal substeps take */
             const float MAX_ELAPSED_TIME = 3.0f*1.0f / 60.0f*1000.0f;
@@ -327,6 +328,7 @@ void MainLoop::run()
             m_request_abort = true;
         }
 #endif
+
         PROFILER_PUSH_CPU_MARKER("Main loop", 0xFF, 0x00, 0xF7);
 
         left_over_time += getLimitedDt();

src/main_loop.hpp

@@ -37,6 +37,9 @@ private:
     /** True if the frame rate should be throttled. */
     bool m_throttle_fps;
     
+    /** True if dt is not decreased for low fps */
+    bool m_allow_large_dt;
+
     bool m_frame_before_loading_world;
 
     Synchronised<int> m_ticks_adjustment;
@@ -54,6 +57,7 @@ public:
     void abort() { m_abort = true; }
     void requestAbort() { m_request_abort = true; }
     void setThrottleFPS(bool throttle) { m_throttle_fps = throttle; }
+    void setAllowLargeDt(bool enable) { m_allow_large_dt = enable; }
     // ------------------------------------------------------------------------
     /** Returns true if STK is to be stoppe. */
     bool isAborted() const { return m_abort; }

src/modes/cutscene_world.cpp

@@ -17,6 +17,7 @@
 
 #include "modes/cutscene_world.hpp"
 
+#include "main_loop.hpp"
 #include "animations/animation_base.hpp"
 #include "animations/three_d_animation.hpp"
 #include "audio/sfx_manager.hpp"
@@ -71,6 +72,9 @@ CutsceneWorld::CutsceneWorld() : World()
  */
 void CutsceneWorld::init()
 {
+    // Use real dt even if fps is low. It allows to keep everything synchronized
+    main_loop->setAllowLargeDt(true);
+    
     m_second_reset = false;
     World::init();
 
@@ -170,6 +174,7 @@ void CutsceneWorld::init()
  */
 CutsceneWorld::~CutsceneWorld()
 {
+    main_loop->setAllowLargeDt(false);
 }   // ~CutsceneWorld
 //-----------------------------------------------------------------------------
 void CutsceneWorld::reset(bool restart)