Another attempt to fix wind

src/object/player.cpp

@@ -101,6 +101,7 @@ const float OVERSPEED_DECELERATION = 100;
 
 /** multiplied by WALK_ACCELERATION to give friction */
 const float NORMAL_FRICTION_MULTIPLIER = 1.5f;
+const float STATIC_FRICTION_MULTIPLIER = 2.0f;
 /** multiplied by WALK_ACCELERATION to give friction */
 const float ICE_FRICTION_MULTIPLIER = 0.1f;
 const float ICE_ACCELERATION_MULTIPLIER = 0.25f;
@@ -629,7 +630,7 @@ Player::update(float dt_sec)
   }
 
   if (!m_dying && !m_deactivated)
-    handle_input();
+    handle_input(dt_sec);
 
   /*
   // handle_input() calls apply_friction() when Tux is not walking, so we'll have to do this ourselves
@@ -956,7 +957,7 @@ Player::update(float dt_sec)
 }
 
 void
-Player::slide()
+Player::slide(float dt_sec)
 {
   if (m_swimming || m_water_jump || m_stone)
   {
@@ -1005,7 +1006,7 @@ Player::slide()
       if (m_floor_normal.y == 0.f && m_can_jump)
       {
         if (!m_slidejumping && !m_jumping) {
-          apply_friction();
+          apply_friction(dt_sec);
         }
       }
       else
@@ -1158,30 +1159,31 @@ Player::swim(float pointx, float pointy, bool boost)
 }
 
 void
-Player::apply_friction()
+Player::apply_friction(float dt_sec)
 {
   bool is_on_ground = on_ground();
   float velx = m_physic.get_velocity_x();
-  if (is_on_ground && (fabsf(velx) < (m_stone ? 5.f : WALK_SPEED))) {
+  /*if (is_on_ground && (fabsf(velx) < (m_stone ? 5.f : WALK_SPEED))) {
     m_physic.set_velocity_x(0);
     m_physic.set_acceleration_x(0);
     return;
-  }
+  }*/
   float friction = WALK_ACCELERATION_X;
   if (m_on_ice && is_on_ground)
     //we need this or else sliding on ice will cause Tux to go on for a very long time
     friction *= (ICE_FRICTION_MULTIPLIER*(m_sliding ? 4.f : m_stone ? 5.f : 1.f));
   else
     friction *= (NORMAL_FRICTION_MULTIPLIER*(m_sliding ? 0.8f : m_stone ? 0.4f : 1.f));
+  if (is_on_ground && (fabsf(velx) < (m_stone ? 5.f : WALK_SPEED))) friction *= STATIC_FRICTION_MULTIPLIER;
   if (velx < 0) {
-    m_physic.set_acceleration_x(friction);
+    m_physic.accelerate_x(friction, dt_sec, 0.0f);
   } else if (velx > 0) {
-    m_physic.set_acceleration_x(-friction);
+    m_physic.accelerate_x(-friction, dt_sec, 0.0f);
   } // no friction for physic.get_velocity_x() == 0
 }
 
 void
-Player::handle_horizontal_input()
+Player::handle_horizontal_input(float dt_sec)
 {
   float vx = m_physic.get_velocity_x();
   float vy = m_physic.get_velocity_y();
@@ -1295,7 +1297,7 @@ Player::handle_horizontal_input()
 
   // we get slower when not pressing any keys
   if (dirsign == 0) {
-    apply_friction();
+    apply_friction(dt_sec);
   }
 }
 
@@ -1538,7 +1540,7 @@ Player::handle_vertical_input()
 }
 
 void
-Player::handle_input()
+Player::handle_input(float dt_sec)
 {
   // Display the player's ID on top of them at the beginning of the level/sector
   // and persist the number until the player moves, because players will be
@@ -1560,7 +1562,7 @@ Player::handle_input()
     return;
   }
   if (m_stone) {
-    handle_input_rolling();
+    handle_input_rolling(dt_sec);
     return;
   }
   if (m_swimming) {
@@ -1607,7 +1609,7 @@ Player::handle_input()
     m_peekingY = Direction::DOWN;
 
   /* Handle horizontal movement: */
-  if (!m_backflipping && !m_stone && !m_swimming && !m_sliding) handle_horizontal_input();
+  if (!m_backflipping && !m_stone && !m_swimming && !m_sliding) handle_horizontal_input(dt_sec);
 
   /* Jump/jumping? */
   if (on_ground())
@@ -1654,7 +1656,7 @@ Player::handle_input()
   }
 
   if (m_stone)
-    apply_friction();
+    apply_friction(dt_sec);
 
   /* Duck or Standup! */
   if (((m_controller->pressed(Control::DOWN) && !m_growing && !m_stone) || ((m_duck || m_wants_buttjump || m_crawl) && m_controller->hold(Control::DOWN))) &&
@@ -1745,7 +1747,7 @@ Player::handle_input()
   if (m_sliding)
   {
     adjust_height(DUCKED_TUX_HEIGHT);
-    slide();
+    slide(dt_sec);
   }
   else if (!m_sliding && (m_coyote_timer.started()) && !m_skidding_timer.started() &&
     (m_floor_normal.y != 0 || (m_controller->hold(Control::LEFT) || m_controller->hold(Control::RIGHT)))
@@ -1754,7 +1756,7 @@ Player::handle_input()
   {
     sideways_push(m_dir == Direction::LEFT ? -100.f : 100.f);
     adjust_height(DUCKED_TUX_HEIGHT);
-    slide();
+    slide(dt_sec);
   }
 }
 
@@ -2755,7 +2757,7 @@ Player::handle_input_climbing()
 }
 
 void
-Player::handle_input_rolling()
+Player::handle_input_rolling(float dt_sec)
 {
   // handle exiting
   if (m_stone)
@@ -2834,7 +2836,7 @@ Player::handle_input_rolling()
       m_physic.set_acceleration_x(ax + sx);
     }
     else {
-      apply_friction();
+      apply_friction(dt_sec);
     }
   }
 }

src/object/player.hpp

@@ -461,14 +461,14 @@ class Player final : public MovingObject
   bool track_state() const override { return false; }
 
 private:
-  void handle_input();
+  void handle_input(float dt_sec);
   void handle_input_ghost(); /**< input handling while in ghost mode */
   void handle_input_climbing(); /**< input handling while climbing */
-  void handle_input_rolling();
+  void handle_input_rolling(float dt_sec);
 
   void handle_input_swimming();
 
-  void handle_horizontal_input();
+  void handle_horizontal_input(float dt_sec);
   void handle_vertical_input();
 
   /** Set Tux's position, reset state and velocity. */
@@ -477,13 +477,13 @@ class Player final : public MovingObject
   void do_jump_apex();
   void early_jump_apex();
 
-  void slide();
+  void slide(float dt_sec);
   void swim(float pointx, float pointy, bool boost);
 
   BonusType string_to_bonus(const std::string& bonus) const;
 
   /** slows Tux down a little, based on where he's standing */
-  void apply_friction();
+  void apply_friction(float dt_sec);
 
   void check_bounds();
 

src/object/wind.cpp

@@ -28,6 +28,7 @@
 #include "object/sprite_particle.hpp"
 #include "sprite/sprite.hpp"
 #include "sprite/sprite_manager.hpp"
+#include "supertux/physic.hpp"
 #include "supertux/sector.hpp"
 #include "util/reader_mapping.hpp"
 #include "video/drawing_context.hpp"
@@ -132,6 +133,31 @@ Wind::draw(DrawingContext& context)
   }
 }
 
+Vector
+Wind::get_induced_acceleration(const Rectf& bbox, const Physic& physic) const
+{
+  const float coef = 1/28.8;
+  const Vector rel_speed = speed - physic.get_velocity();
+  if (rel_speed.x == 0 && rel_speed.y == 0) {
+    return rel_speed; // no relative movement = no drag = no force = no acceleration
+  }
+  const float v2 = glm::length2(rel_speed);
+  const float v = std::sqrt(v2);
+  // "length" of the object in the direction of the wind
+  const float l = bbox.get_width() * std::fabs(rel_speed.x / v)
+                + bbox.get_height() * std::fabs(rel_speed.y / v);
+  // induced acceleration
+  const float a = coef * v2 / l;
+  return a * (rel_speed / v);
+}
+
+void
+Wind::accelerate_object(const MovingObject* other, Physic& physic)
+{
+  const Vector acceleration = get_induced_acceleration(other->get_bbox(), physic);
+  physic.accelerate(acceleration, dt_sec, speed);
+}
+
 HitResponse
 Wind::collision(MovingObject& other, const CollisionHit& )
 {
@@ -141,7 +167,9 @@ Wind::collision(MovingObject& other, const CollisionHit& )
   if (player && affects_player)
   {
     player->override_velocity();
-    if (!player->on_ground())
+    //player->add_velocity(get_induced_acceleration(player, player->get_physic()) * dt_sec, speed);
+    accelerate_object(player, player->get_physic());
+    /*if (!player->on_ground())
 	  {
       player->add_velocity(speed * acceleration * dt_sec, speed);
     }
@@ -156,19 +184,21 @@ Wind::collision(MovingObject& other, const CollisionHit& )
 	      // When on ground, get blown slightly differently, but the max speed is less than it would be otherwise seen as we take "friction" into account
 	      player->add_velocity((Vector(speed.x, 0) * 0.1f) * (acceleration+1), (Vector(speed.x, speed.y) * 0.5f));
 	    }
-    }
+    }*/
   }
 
   auto badguy = dynamic_cast<BadGuy*>(&other);
   if (badguy && affects_badguys && badguy->can_be_affected_by_wind())
   {
-    badguy->add_wind_velocity(speed * acceleration * dt_sec, speed);
+    //badguy->add_wind_velocity(get_induced_acceleration(badguy, badguy->get_physic()) * dt_sec, speed);
+    accelerate_object(badguy, badguy->get_physic());
   }
 
   auto rock = dynamic_cast<Rock*>(&other);
   if (rock && affects_objects)
   {
-    rock->add_wind_velocity(speed * acceleration * dt_sec, speed);
+    //rock->add_wind_velocity(get_induced_acceleration(rock, rock->get_physic()) * dt_sec, speed);
+    accelerate_object(rock, rock->get_physic());
   }
 
   return ABORT_MOVE;

src/object/wind.hpp

@@ -21,6 +21,7 @@
 
 #include "video/layer.hpp"
 
+class Physic;
 class ReaderMapping;
 
 /** Defines an area that will gently push Players in one direction */
@@ -70,11 +71,14 @@ class Wind final : public MovingObject
    */
   virtual int get_layer() const override { return m_layer; }
 
+  // Returns induced acceleration onto an object, approximated from maximal speeds and accelerations
+  Vector get_induced_acceleration(const Rectf& bbox, const Physic& physic) const;
+
 private:
   int m_layer;
   bool blowing; /**< true if wind is currently switched on */
   Vector speed;
-  float acceleration;
+  float acceleration; // legacy value
   Vector new_size;
 
   float dt_sec; /**< stores last dt_sec gotten at update() */
@@ -84,6 +88,8 @@ class Wind final : public MovingObject
   bool affects_player; /**< whether the wind can affect the player: useful for cinematic wind */
   bool fancy_wind;
   bool particles_enabled;
+
+  void accelerate_object(const MovingObject* other, Physic& physic);
 
 private:
   Wind(const Wind&) = delete;

src/supertux/physic.cpp

@@ -20,8 +20,8 @@
 #include "supertux/sector.hpp"
 
 Physic::Physic() :
-  ax(0), ay(0),
-  vx(0), vy(0),
+  a(0, 0),
+  v(0, 0),
   gravity_enabled_flag(true),
   gravity_modifier(1.0f)
 {
@@ -30,22 +30,20 @@ Physic::Physic() :
 void
 Physic::reset()
 {
-  ax = ay = vx = vy = 0;
+  a.x = a.y = v.x = v.y = 0;
   gravity_enabled_flag = true;
 }
 
 void
 Physic::set_velocity(const Vector& vector)
 {
-  vx = vector.x;
-  vy = vector.y;
+  v = vector;
 }
 
 void
 Physic::set_acceleration(const Vector& vector)
 {
-  ax = vector.x;
-  ay = vector.y;
+  a = vector;
 }
 
 Vector
@@ -56,11 +54,47 @@ Physic::get_movement(float dt_sec)
   // Semi-implicit Euler integration
   // with constant acceleration, this will result in a position delta of
   // v t + .5 a t (t+dt_sec) at total time t
-  vx += ax * dt_sec;
-  vy += (ay + grav) * dt_sec;
-  Vector result(vx * dt_sec, vy * dt_sec);
+  v.x += a.x * dt_sec;
+  v.y += (a.y + grav) * dt_sec;
+  Vector result(v.x * dt_sec, v.y * dt_sec);
 
   return result;
 }
 
+void
+Physic::accelerate(const Vector& acceleration, float dt_sec, const Vector& target_velocity)
+{
+  const Vector v_contr = acceleration * dt_sec;
+  const Vector new_v = v + v_contr;
+  if (glm::dot(v_contr, target_velocity - new_v) < 0) {
+    v = target_velocity; // overshot detected, trimming velocity
+  } else {
+    v = new_v;
+  }
+}
+
+void
+Physic::accelerate_x(float acceleration, float dt_sec, float target_velocity)
+{
+  const float v_contr = acceleration * dt_sec;
+  const float new_v = v.x + v_contr;
+  if (v_contr * (target_velocity - new_v) < 0) {
+    v.x = target_velocity;
+  } else {
+    v.x = new_v;
+  }
+}
+
+void
+Physic::accelerate_y(float acceleration, float dt_sec, float target_velocity)
+{
+  const float v_contr = acceleration * dt_sec;
+  const float new_v = v.y + v_contr;
+  if (v_contr * (target_velocity - new_v) < 0) {
+    v.y = target_velocity;
+  } else {
+    v.y = new_v;
+  }
+}
+
 /* EOF */