Fix all known instances of kart flying due to cushioning

src/karts/rescue_animation.cpp

@@ -25,6 +25,7 @@
 #include "karts/kart_properties.hpp"
 #include "modes/three_strikes_battle.hpp"
 #include "network/network_config.hpp"
+#include "physics/btKart.hpp"
 #include "physics/physics.hpp"
 #include "physics/triangle_mesh.hpp"
 #include "tracks/drive_graph.hpp"
@@ -60,6 +61,7 @@ RescueAnimation::RescueAnimation(AbstractKart *kart, bool is_auto_rescue)
     m_up_vector   = m_kart->getTrans().getBasis().getColumn(1);
     m_xyz         = m_kart->getXYZ();
     m_kart->getAttachment()->clear();
+    m_kart->getVehicle()->resetGroundHeight();
 
     if (NetworkConfig::get()->isNetworking() &&
         NetworkConfig::get()->isServer())

src/physics/btKart.cpp

@@ -131,14 +131,22 @@ void btKart::reset()
     m_max_speed                  = -1.0f;
     m_min_speed                  = 0.0f;
     m_cushioning_disable_time    = 0;
-    m_ground_height              = 0;
+    resetGroundHeight();
-    m_ground_height_old          = 0;
 
     // Set the brakes so that karts don't slide downhill
     setAllBrakes(5.0f);
 
 }   // reset
 
+// ----------------------------------------------------------------------------
+/** Resets the ground height of a kart. This is also called on rescues.
+ */
+void btKart::resetGroundHeight()
+{
+    m_ground_height              = 0.15;
+    m_ground_height_old          = 0.15;
+}   // resetGroundHeight
+
 // ----------------------------------------------------------------------------
 const btTransform& btKart::getWheelTransformWS( int wheelIndex ) const
 {
@@ -530,7 +538,7 @@ void btKart::updateVehicle( btScalar step )
     btVector3 down = -m_chassisBody->getGravity();
     down.normalize();
     btVector3 v_down = (v * down) * down;
-    btScalar offset=0.1f;
+    btScalar offset=0.24;
 
 #ifdef DEBUG_CUSHIONING
     Log::verbose("physics",
@@ -551,18 +559,15 @@ void btKart::updateVehicle( btScalar step )
     // to the predicted kart movement, which was found experimentally:
     btScalar gravity = m_chassisBody->getGravity().length();
 
+    btScalar absolute_fall = step*(-v_down.getY() + gravity*step);
     btScalar predicted_fall = gravity*step*step +
                               (m_ground_height_old-m_ground_height);
 
-    // Limit kart jumping upward brutally if landing just
+    // if the ground_height is below offset-0.01f ;
-    // after a sudden terrain height change ;
+    // the terrain has unexpectedly changed - avoid sending the kart flying
-    // no jump in STK is so big to normally go over this value
+    if (absolute_fall > 0.06 && m_cushioning_disable_time==0 &&
-    if (predicted_fall > 0.4) predicted_fall = 0.4;
-
-    if (v_down.getY()<0 && m_cushioning_disable_time==0 &&
         m_ground_height < predicted_fall + offset &&
-        m_ground_height > 0 && m_ground_height_old > 0.3 &&
+        m_ground_height > (offset-0.01f) && m_ground_height_old > 0.3)
-        predicted_fall > 0.05)
     {
         // Disable more cushioning for 1 second. This avoids the problem
         // of hovering: a kart gets cushioned on a down-sloping area, still

src/physics/btKart.hpp

@@ -148,6 +148,7 @@ public:
                               Kart *kart);
      virtual          ~btKart();
     void               reset();
+    void               resetGroundHeight();
     void               debugDraw(btIDebugDraw* debugDrawer);
     const btTransform& getChassisWorldTransform() const;
     btScalar           rayCast(unsigned int index, float fraction=1.0f);