Fix formula used for acceleration (#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 @@ public:
 	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;
 		}