Fix formula used for acceleration (minetest#12353)

doc/breakages.md

@@ -3,6 +3,7 @@
 This document contains a list of breaking changes to be made in the next major version.
 
 * Remove attachment space multiplier (*10)
+* Remove player gravity multiplier (*2)
 * `get_sky()` returns a table (without arg)
 * `game.conf` name/id mess
 * remove `depends.txt` / `description.txt` (would simplify ContentDB and Minetest code a little)

src/client/clientenvironment.cpp

@@ -195,21 +195,24 @@ void ClientEnvironment::step(float dtime)
  lplayer->applyControl(dtime_part, this);
 
  // Apply physics
+ lplayer->gravity = 0;
  if (!free_move) {
  // Gravity
- v3f speed = lplayer->getSpeed();
  if (!is_climbing && !lplayer->in_liquid)
- speed.Y -= lplayer->movement_gravity *
-  lplayer->physics_override.gravity * dtime_part * 2.0f;
+ // HACK the factor 2 for gravity is arbitrary and should be removed eventually
+ lplayer->gravity = 2 * lplayer->movement_gravity * lplayer->physics_override.gravity;
 
  // Liquid floating / sinking
  if (!is_climbing && lplayer->in_liquid &&
  !lplayer->swimming_vertical &&
  !lplayer->swimming_pitch)
- speed.Y -= lplayer->movement_liquid_sink * dtime_part * 2.0f;
+ // HACK the factor 2 for gravity is arbitrary and should be removed eventually
+ lplayer->gravity = 2 * lplayer->movement_liquid_sink;
 
  // Movement resistance
  if (lplayer->move_resistance > 0) {
+ v3f speed = lplayer->getSpeed();
+
  // How much the node's move_resistance blocks movement, ranges
  // between 0 and 1. Should match the scale at which liquid_viscosity
  // increase affects other liquid attributes.
@@ -232,15 +235,16 @@ void ClientEnvironment::step(float dtime)
  (1 - resistance_factor);
  v3f d = d_wanted.normalize() * (dl * dtime_part * 100.0f);
  speed += d;
- }
 
- lplayer->setSpeed(speed);
+ lplayer->setSpeed(speed);
+ }
  }
 
  /*
  Move the lplayer.
  This also does collision detection.
  */
+
  lplayer->move(dtime_part, this, position_max_increment,
  &player_collisions);
  }

src/client/localplayer.cpp

@@ -292,7 +292,7 @@ void LocalPlayer::move(f32 dtime, Environment *env, f32 pos_max_d,
  float player_stepheight = (m_cao == nullptr) ? 0.0f :
  (touching_ground ? m_cao->getStepHeight() : (0.2f * BS));
 
- v3f accel_f;
+ v3f accel_f(0, -gravity, 0);
  const v3f initial_position = position;
  const v3f initial_speed = m_speed;
 
@@ -778,6 +778,9 @@ void LocalPlayer::old_move(f32 dtime, Environment *env, f32 pos_max_d,
  m_speed += m_added_velocity;
  m_added_velocity = v3f(0.0f);
 
+ // Apply gravity (note: this is broken, but kept since this is *old* move code)
+ m_speed.Y -= gravity * dtime;
+
  /*
  Collision detection
  */
@@ -1117,8 +1120,10 @@ void LocalPlayer::handleAutojump(f32 dtime, Environment *env,
  }
  }
 
- float jump_height = 1.1f; // TODO: better than a magic number
- v3f jump_pos = initial_position + v3f(0.0f, jump_height * BS, 0.0f);
+ float jumpspeed = movement_speed_jump * physics_override.jump;
+ float peak_dtime = jumpspeed / gravity; // at the peak of the jump v = gt <=> t = v / g
+ float jump_height = (jumpspeed - 0.5f * gravity * peak_dtime) * peak_dtime; // s = vt - 1/2 gt^2
+ v3f jump_pos = initial_position + v3f(0.0f, jump_height, 0.0f);
  v3f jump_speed = initial_speed;
 
  // try at peak of jump, zero step height

src/client/localplayer.h

@@ -62,6 +62,8 @@ class LocalPlayer : public Player
  bool swimming_vertical = false;
  bool swimming_pitch = false;
 
+ f32 gravity = 0; // total downwards acceleration
+
  void move(f32 dtime, Environment *env, f32 pos_max_d);
  void move(f32 dtime, Environment *env, f32 pos_max_d,
  std::vector<CollisionInfo> *collision_info);

src/client/particles.cpp

@@ -217,9 +217,10 @@ void Particle::step(float dtime)
  }
  m_pos = p_pos / BS;
  } else {
- // apply acceleration
+ // apply velocity and acceleration to position
+ m_pos += (m_velocity + m_acceleration * 0.5f * dtime) * dtime;
+ // apply acceleration to velocity
  m_velocity += m_acceleration * dtime;
- m_pos += m_velocity * dtime;
  }
 
  if (m_animation.type != TAT_NONE) {

src/collision.cpp

@@ -249,10 +249,12 @@ collisionMoveResult collisionMoveSimple(Environment *env, IGameDef *gamedef,
  } else {
  time_notification_done = false;
  }
+
+ v3f newpos_f = *pos_f + (*speed_f + accel_f * 0.5f * dtime) * dtime;
  *speed_f += accel_f * dtime;
 
- // If there is no speed, there are no collisions
- if (speed_f->getLength() == 0)
+ // If the object is static, there are no collisions
+ if (newpos_f == *pos_f)
  return result;
 
  // Limit speed for avoiding hangs
@@ -270,7 +272,6 @@ collisionMoveResult collisionMoveSimple(Environment *env, IGameDef *gamedef,
  //TimeTaker tt2("collisionMoveSimple collect boxes");
  ScopeProfiler sp2(g_profiler, "collisionMoveSimple(): collect boxes", SPT_AVG);
 
- v3f newpos_f = *pos_f + *speed_f * dtime;
  v3f minpos_f(
  MYMIN(pos_f->X, newpos_f.X),
  MYMIN(pos_f->Y, newpos_f.Y) + 0.01f * BS, // bias rounding, player often at +/-n.5

src/server/luaentity_sao.cpp

@@ -175,8 +175,7 @@ void LuaEntitySAO::step(float dtime, bool send_recommended)
  m_velocity = p_velocity;
  m_acceleration = p_acceleration;
  } else {
- m_base_position += dtime * m_velocity + 0.5 * dtime
- * dtime * m_acceleration;
+ m_base_position += (m_velocity + m_acceleration * 0.5f * dtime) * dtime;
  m_velocity += dtime * m_acceleration;
  }