Exported door model, added CollisionManager#on_ground?(entity), made gravity work in PhyisicsManager if Entity has physics enabled, updated test map

lib/managers/physics_manager.rb

@@ -15,21 +15,24 @@ class IMICFPS
     end
 
     def resolve(entity, other)
-      if other.is_a?(Terrain)
-        entity.velocity.y = 0 if entity.velocity.y < 0
-      else
-        entity.velocity.y = other.velocity.y if other.velocity.y < entity.velocity.y && entity.velocity.y < 0
-      end
+      entity.velocity.y = other.velocity.y if other.velocity.y < entity.velocity.y && entity.velocity.y < 0
     end
 
     def simulate
       @collision_manager.game_state.entities.each do |entity|
-        entity.velocity.x *= entity.drag
-        entity.velocity.z *= entity.drag
-
         entity.position.x += entity.velocity.x * entity.delta_time
         entity.position.y += entity.velocity.y * entity.delta_time
         entity.position.z += entity.velocity.z * entity.delta_time
+
+        on_ground = @collision_manager.on_ground?(entity)
+        entity.velocity.x *= entity.drag
+        entity.velocity.z *= entity.drag
+
+        if on_ground
+          entity.velocity.y = 0
+        else
+          entity.velocity.y -= IMICFPS::GRAVITY * entity.delta_time if entity.physics
+        end
       end
     end
   end