Squash and stretch player sprite with sudden changes in vertical momentum

Stretch with a sudden increase of
momentum, squash with a decrease.

src/d_player.h

@@ -597,6 +597,7 @@ typedef struct player_s
 
 	fixed_t speed; // Player's speed (distance formula of MOMX and MOMY values)
 	fixed_t lastspeed;
+	fixed_t lastmomz;
 	UINT8 secondjump; // Jump counter
 
 	UINT8 fly1; // Tails flying

src/k_kart.c

@@ -2288,6 +2288,7 @@ void K_KartMoveAnimation(player_t *player)
 
 	// Update lastspeed value -- we use to display slow driving frames instead of fast driving when slowing down.
 	player->lastspeed = player->speed;
+	player->lastmomz = player->mo->momz;
 }
 
 static void K_TauntVoiceTimers(player_t *player)

src/p_user.c

@@ -1845,6 +1845,41 @@ static void P_DoBubbleBreath(player_t *player)
 	}
 }
 
+static void squish(player_t *player)
+{
+	const fixed_t maxstretch = 2*FRACUNIT;
+	const fixed_t factor = 3 * player->mo->height / 2;
+	const fixed_t threshold = factor / 6;
+
+	const fixed_t old3dspeed = abs(player->lastmomz);
+	const fixed_t new3dspeed = abs(player->mo->momz);
+
+	const fixed_t delta = abs(old3dspeed - new3dspeed);
+
+	if (delta > threshold)
+	{
+		player->mo->spritexscale =
+			FRACUNIT + FixedDiv(delta, factor);
+
+		if (player->mo->spritexscale > maxstretch)
+			player->mo->spritexscale = maxstretch;
+
+		if (abs(new3dspeed) > abs(old3dspeed))
+		{
+			player->mo->spritexscale =
+				FixedDiv(FRACUNIT, player->mo->spritexscale);
+		}
+	}
+	else
+	{
+		player->mo->spritexscale -=
+			(player->mo->spritexscale - FRACUNIT) / 8;
+	}
+
+	player->mo->spriteyscale =
+		FixedDiv(FRACUNIT, player->mo->spritexscale);
+}
+
 //#define OLD_MOVEMENT_CODE 1
 static void P_3dMovement(player_t *player)
 {
@@ -2031,6 +2066,8 @@ static void P_3dMovement(player_t *player)
 			}
 		}
 	}
+
+	squish(player);
 }
 
 //