Update underwater physics

- Reduce steering effect and remove increased friction.
- Strafe into turns and tilt the inside wheels up.

src/d_player.h

@@ -394,6 +394,8 @@ typedef struct player_s
 	INT32 aizdrifttilt;
 	INT32 aizdriftturn;
 
+	INT32 underwatertilt;
+
 	fixed_t offroad;		// In Super Mario Kart, going offroad has lee-way of about 1 second before you start losing speed
 	UINT8 waterskip;		// Water skipping counter
 

src/k_kart.c

@@ -7565,7 +7565,7 @@ static INT16 K_GetKartDriftValue(player_t *player, fixed_t countersteer)
 		basedrift += (basedrift / greasetics) * player->tiregrease;
 	}
 
-	if (player->mo->eflags & (MFE_UNDERWATER|MFE_TOUCHWATER))
+	if (player->mo->eflags & (MFE_TOUCHWATER))
 	{
 		countersteer = FixedMul(countersteer, 3*FRACUNIT/2);
 	}
@@ -7672,7 +7672,11 @@ INT16 K_GetKartTurnValue(player_t *player, INT16 turnvalue)
 		turnfixed = FixedMul(turnfixed, FRACUNIT + player->handleboost);
 	}
 
-	if (player->mo->eflags & (MFE_UNDERWATER|MFE_TOUCHWATER))
+	if (player->mo->eflags & MFE_UNDERWATER)
+	{
+		turnfixed /= 2;
+	}
+	else if (player->mo->eflags & MFE_TOUCHWATER)
 	{
 		turnfixed = FixedMul(turnfixed, 3*FRACUNIT/2);
 	}
@@ -7683,6 +7687,19 @@ INT16 K_GetKartTurnValue(player_t *player, INT16 turnvalue)
 	return (turnfixed / FRACUNIT);
 }
 
+INT32 K_GetUnderwaterTurnAdjust(player_t *player)
+{
+	if (player->mo->eflags & MFE_UNDERWATER)
+	{
+		INT32 steer = (K_GetKartTurnValue(player,
+					player->steering) << TICCMD_REDUCE);
+		return FixedMul(steer, 8 * FixedDiv(player->speed,
+					2 * K_GetKartSpeed(player, false) / 3));
+	}
+	else
+		return 0;
+}
+
 INT32 K_GetKartDriftSparkValue(player_t *player)
 {
 	return (26*4 + player->kartspeed*2 + (9 - player->kartweight))*8;
@@ -8449,7 +8466,7 @@ void K_AdjustPlayerFriction(player_t *player)
 	*/
 
 	// Water gets ice physics too
-	if (player->mo->eflags & (MFE_UNDERWATER|MFE_TOUCHWATER))
+	if (player->mo->eflags & MFE_TOUCHWATER)
 	{
 		player->mo->friction += 614;
 	}

src/k_kart.h

@@ -92,6 +92,7 @@ void K_UpdateDistanceFromFinishLine(player_t *const player);
 boolean K_CheckPlayersRespawnColliding(INT32 playernum, fixed_t x, fixed_t y);
 void K_UpdateSteeringValue(player_t *player, INT16 destSteering);
 INT16 K_GetKartTurnValue(player_t *player, INT16 turnvalue);
+INT32 K_GetUnderwaterTurnAdjust(player_t *player);
 INT32 K_GetKartDriftSparkValue(player_t *player);
 INT32 K_StairJankFlip(INT32 value);
 INT32 K_GetKartDriftSparkValueForStage(player_t *player, UINT8 stage);

src/p_saveg.c

@@ -239,6 +239,8 @@ static void P_NetArchivePlayers(void)
 		WRITEINT32(save_p, players[i].aizdrifttilt);
 		WRITEINT32(save_p, players[i].aizdriftturn);
 
+		WRITEINT32(save_p, players[i].underwatertilt);
+
 		WRITEFIXED(save_p, players[i].offroad);
 		WRITEUINT8(save_p, players[i].waterskip);
 
@@ -495,6 +497,8 @@ static void P_NetUnArchivePlayers(void)
 		players[i].aizdrifttilt = READINT32(save_p);
 		players[i].aizdriftturn = READINT32(save_p);
 
+		players[i].underwatertilt = READINT32(save_p);
+
 		players[i].offroad = READFIXED(save_p);
 		players[i].waterskip = READUINT8(save_p);
 

src/p_user.c

@@ -1769,6 +1769,42 @@ static void P_3dMovement(player_t *player)
 		if (player->mo->movefactor != FRACUNIT) // Friction-scaled acceleration...
 			movepushforward = FixedMul(movepushforward, player->mo->movefactor);
 
+		{
+			INT32 a = K_GetUnderwaterTurnAdjust(player);
+			INT32 adj = 0;
+
+			if (a)
+			{
+				 adj = a / 4;
+
+				if (abs(player->underwatertilt + adj) > abs(a))
+					adj = (a - player->underwatertilt);
+
+				if (abs(a) < abs(player->underwatertilt))
+					adj = 0;
+
+				movepushangle += a;
+			}
+
+			if (adj)
+			{
+				player->underwatertilt += adj;
+
+				if (abs(player->underwatertilt) > ANG30)
+				{
+					player->underwatertilt =
+						player->underwatertilt > 0 ? ANG30
+						: -(ANG30);
+				}
+			}
+			else
+			{
+				player->underwatertilt =
+					FixedMul(player->underwatertilt,
+							7*FRACUNIT/8);
+			}
+		}
+
 		totalthrust.x += P_ReturnThrustX(player->mo, movepushangle, movepushforward);
 		totalthrust.y += P_ReturnThrustY(player->mo, movepushangle, movepushforward);
 	}
@@ -2055,6 +2091,10 @@ void P_MovePlayer(player_t *player)
 			else if (player->drift != 0)
 			{
 				INT32 a = (ANGLE_45 / 5) * player->drift;
+
+				if (player->mo->eflags & MFE_UNDERWATER)
+					a /= 2;
+
 				player->drawangle += a;
 			}
 		}

src/r_patchrotation.c

@@ -42,7 +42,11 @@ static angle_t R_PlayerSpriteRotation(player_t *player, player_t *viewPlayer)
 
 	angle_t rollAngle = 0;
 
-	if (sliptideLift)
+	if (player->mo->eflags & MFE_UNDERWATER)
+	{
+		rollAngle -= player->underwatertilt;
+	}
+	else if (sliptideLift)
 	{
 		/* (from side) tilt downward if turning
 		   toward camera, upward if away. */