Started to set the gravity for selected material based on the

normal of the triangle where the kart is on.

src/graphics/material.cpp

@@ -146,6 +146,7 @@ Material::Material(const XMLNode *node, int index, bool deprecated)
 
     node->get("water-splash",     &m_water_splash      );
     node->get("jump",             &m_is_jump_texture   );
+    node->get("has-gravity",      &m_has_gravity       );
 
     if (m_collision_reaction != NORMAL)
     {
@@ -344,6 +345,10 @@ Material::Material(const XMLNode *node, int index, bool deprecated)
         }
 
     }   // for i <node->getNumNodes()
+
+    if(m_has_gravity)
+        m_high_tire_adhesion = true;
+
     install(/*is_full_path*/false);
 }   // Material
 
@@ -410,6 +415,7 @@ void Material::init(unsigned int index)
     m_is_heightmap              = false;
     m_water_splash              = false;
     m_is_jump_texture           = false;
+    m_has_gravity               = false;
 
     for (int n=0; n<EMIT_KINDS_COUNT; n++)
     {

src/graphics/material.hpp

@@ -111,6 +111,11 @@ private:
      *  leaving it and being in the air. */
     bool             m_is_jump_texture;
 
+    /** True if driving on this texture should adjust the gravity of the kart
+     *  to be along the normal of the triangle. This allows karts to drive e.g
+     *  upside down. */
+    bool             m_has_gravity;
+
     /** Speed of the 'main' wave in the water shader. Only used if
         m_graphical_effect == WATER_SHADER */
     float            m_water_shader_speed_1;
@@ -312,6 +317,11 @@ public:
      *  jump animation. */
     bool isJumpTexture() const { return m_is_jump_texture; }
     // ------------------------------------------------------------------------
+    /** Returns true if this texture adjusts the gravity vector of the kart
+     *  to be parallel to the normal of the triangle - which allows karts to
+     *  e.g. drive upside down. */
+    bool hasGravity() const { return m_has_gravity; }
+    // ------------------------------------------------------------------------
     /** Returns the zipper parametersfor the current material. */
     void getZipperParameter(float *zipper_max_speed_increase,
                              float *zipper_duration,

src/karts/kart.cpp

@@ -1212,6 +1212,10 @@ void Kart::update(float dt)
     const Material* material=m_terrain_info->getMaterial();
     if (!material)   // kart falling off the track
     {
+        Vec3 gravity(0, -9.8f, 0);
+        btRigidBody *body = getVehicle()->getRigidBody();
+        body->setGravity(gravity);
+
         // let kart fall a bit before rescuing
         const Vec3 *min, *max;
         World::getWorld()->getTrack()->getAABB(&min, &max);
@@ -1221,6 +1225,16 @@ void Kart::update(float dt)
     }
     else
     {
+        Vec3 gravity(0.0f, -9.8f, 0.0f);
+        btRigidBody *body = getVehicle()->getRigidBody();
+        // If the material should overwrite the gravity, 
+        if(material->hasGravity())
+        {
+            Vec3 normal = m_terrain_info->getNormal();
+            gravity = normal * -9.8f;
+        }
+        body->setGravity(gravity);
+
         handleMaterialSFX(material);
         if     (material->isDriveReset() && isOnGround())
             new RescueAnimation(this);