Made restitution configurable (depending on speed of kart).

data/stk_config.xml

@@ -438,6 +438,11 @@
            period, which results in less abrupt changes. If set to 0,
            the impulse is only applied once.
          resitution: restitution value to be used for the kart rigid bodies.
+           The restitution used depends on the speed to avoid physics issues
+           (a collision with high speed and high restitution will push the
+           kart high up into the air). The values specified are
+           speed:restitution pairs, the actual restitution will be
+           interpolated based on the points specified here.
          bevel-factor: for each point of the chassis collision box one
            additional point is added, resulting in a bevelled box shape.
            The original Z coordinate of the chassis is multiplied by
@@ -457,7 +462,7 @@
            behaviour of the karts. -->
     <collision impulse-type="normal"
                impulse="3000" impulse-time="0.1" terrain-impulse="160"
-               restitution="1.0" bevel-factor="0.5 0.0 0.3"
+               restitution="0:1.0 5:1.0 20:0.2" bevel-factor="0.5 0.0 0.3"
                physical-wheel-position="0" />
 
      <!-- Skidding: increase: multiplicative increase of skidding factor in each frame.

src/karts/kart.cpp

@@ -721,7 +721,7 @@ void Kart::createPhysics()
     btTransform trans;
     trans.setIdentity();
     createBody(mass, trans, &m_kart_chassis,
-               m_kart_properties->getRestitution());
+               m_kart_properties->getRestitution(0.0f));
     std::vector<float> ang_fact = m_kart_properties->getStabilityAngularFactor();
     // The angular factor (with X and Z values <1) helps to keep the kart
     // upright, especially in case of a collision.
@@ -1266,12 +1266,13 @@ void Kart::eliminate()
  */
 void Kart::update(int ticks)
 {
-    if(m_speed < 5.0f)
+    // Make the restitution depend on speed: this avoids collision issues,
-        m_body->setRestitution(1.0f);
+    // otherwise a collision with high speed can see a kart being push
-    else if(m_speed<20.0f)
+    // high up in the air (and out of control). So for higher speed we
-        m_body->setRestitution(1.0f-(m_speed-5.0f)/15.0f);
+    // reduce the restitution, meaning the karts will get less of a push
-    else
+    // based on the collision speed.
-        m_body->setRestitution(0.0f);
+    m_body->setRestitution(m_kart_properties->getRestitution(fabsf(m_speed)));
+
     // Reset any instand speed increase in the bullet kart
     m_vehicle->setMinSpeed(0);
 

src/karts/kart_properties.cpp

@@ -82,7 +82,7 @@ KartProperties::KartProperties(const std::string &filename)
     // Set all other values to undefined, so that it can later be tested
     // if everything is defined properly.
     m_wheel_base = m_friction_slip = m_collision_terrain_impulse =
-        m_collision_impulse = m_restitution = m_collision_impulse_time =
+        m_collision_impulse = m_collision_impulse_time =
         m_max_lean = m_lean_speed = m_physical_wheel_position = UNDEFINED;
 
     m_terrain_impulse_type       = IMPULSE_NONE;
@@ -499,7 +499,7 @@ void KartProperties::getAllData(const XMLNode * root)
 void KartProperties::checkAllSet(const std::string &filename)
 {
 #define CHECK_NEG(  a,strA) if(a<=UNDEFINED) {                      \
-        Log::fatal("[KartProperties]",                                \
+        Log::fatal("KartProperties",                                \
                     "Missing default value for '%s' in '%s'.",    \
                     strA,filename.c_str());                \
     }
@@ -508,9 +508,11 @@ void KartProperties::checkAllSet(const std::string &filename)
     CHECK_NEG(m_collision_terrain_impulse,  "collision terrain-impulse"     );
     CHECK_NEG(m_collision_impulse,          "collision impulse"             );
     CHECK_NEG(m_collision_impulse_time,     "collision impulse-time"        );
-    CHECK_NEG(m_restitution,                "collision restitution"         );
     CHECK_NEG(m_physical_wheel_position,    "collision physical-wheel-position");
 
+    if(m_restitution.size()<1)
+        Log::fatal("KartProperties", "Missing restitution value.");
+
     for(unsigned int i=0; i<RaceManager::DIFFICULTY_COUNT; i++)
         m_ai_properties[i]->checkAllSet(filename);
 }   // checkAllSet

src/karts/kart_properties.hpp

@@ -201,9 +201,8 @@ private:
     /** How long the collision impulse should be applied. */
     float m_collision_impulse_time;
 
-    /** The restitution factor to be used in collsions for this kart. */
+    /** Restitution depending on speed. */
-    float m_restitution;
+    InterpolationArray m_restitution;
-
 
     void  load              (const std::string &filename,
                              const std::string &node);
@@ -340,7 +339,7 @@ public:
 
     // ------------------------------------------------------------------------
     /** Returns the restitution factor for this kart. */
-    float getRestitution            () const { return m_restitution; }
+    float getRestitution(float speed) const { return m_restitution.get(speed);}
 
     // ------------------------------------------------------------------------
     /** Returns a pointer to the AI properties. */