From 4bdc05824c7bd342c08be52690d058b2604ae895 Mon Sep 17 00:00:00 2001
From: James R <justsomejames2@gmail.com>
Date: Sat, 19 Aug 2023 03:24:22 -0700
Subject: [PATCH] Add Obj_BeginEmeraldOrbit, seamless transition into orbit

---
 src/k_objects.h       |  1 +
 src/objects/emerald.c | 94 ++++++++++++++++++++++++++++++++++---------
 src/objects/ufo.c     |  2 +-
 3 files changed, 78 insertions(+), 19 deletions(-)

diff --git a/src/k_objects.h b/src/k_objects.h
index 8066e7078..513f88fdb 100644
--- a/src/k_objects.h
+++ b/src/k_objects.h
@@ -207,6 +207,7 @@ void Obj_SneakerPanelCollide(mobj_t *pad, mobj_t *mo);
 /* Emerald */
 void Obj_SpawnEmeraldSparks(mobj_t *source);
 void Obj_EmeraldThink(mobj_t *emerald);
+void Obj_BeginEmeraldOrbit(mobj_t *emerald, mobj_t *target, fixed_t radius, INT32 revolution_time);
 
 #ifdef __cplusplus
 } // extern "C"
diff --git a/src/objects/emerald.c b/src/objects/emerald.c
index 40524cd12..6ef557b12 100644
--- a/src/objects/emerald.c
+++ b/src/objects/emerald.c
@@ -3,8 +3,16 @@
 #include "../info.h"
 #include "../m_random.h"
 #include "../p_local.h"
+#include "../r_main.h"
 #include "../tables.h"
 
+#define emerald_type(o) ((o)->extravalue1)
+#define emerald_anim_start(o) ((o)->movedir)
+#define emerald_revolution_time(o) ((o)->threshold)
+#define emerald_start_radius(o) ((o)->movecount)
+#define emerald_target_radius(o) ((o)->extravalue2)
+#define emerald_z_shift(o) ((o)->reactiontime)
+
 void Obj_SpawnEmeraldSparks(mobj_t *mobj)
 {
 	if (leveltime % 3 != 0)
@@ -25,31 +33,64 @@ void Obj_SpawnEmeraldSparks(mobj_t *mobj)
 	sparkle->sprzoff = mobj->sprzoff;
 }
 
+static INT32 get_elapsed(mobj_t *emerald)
+{
+	return leveltime - min((tic_t)emerald_anim_start(emerald), leveltime);
+}
+
+static INT32 get_revolve_time(mobj_t *emerald)
+{
+	return max(1, emerald_revolution_time(emerald));
+}
+
+static fixed_t get_suck_factor(mobj_t *emerald)
+{
+	const INT32 suck_time = get_revolve_time(emerald) * 2;
+
+	return (min(get_elapsed(emerald), suck_time) * FRACUNIT) / suck_time;
+}
+
+static fixed_t get_current_radius(mobj_t *emerald)
+{
+	fixed_t s = emerald_start_radius(emerald);
+	fixed_t t = emerald_target_radius(emerald);
+
+	return s + FixedMul(t - s, get_suck_factor(emerald));
+}
+
+static fixed_t get_bob(mobj_t *emerald)
+{
+	angle_t phase = get_elapsed(emerald) * ((ANGLE_MAX / get_revolve_time(emerald)) / 2);
+
+	return FixedMul(30 * mapobjectscale, FSIN(emerald->angle + phase));
+}
+
+static fixed_t center_of(mobj_t *mobj)
+{
+	return mobj->z + (mobj->height / 2);
+}
+
+static fixed_t get_target_z(mobj_t *emerald)
+{
+	fixed_t shift = FixedMul(emerald_z_shift(emerald), FRACUNIT - get_suck_factor(emerald));
+
+	return center_of(emerald->target) + get_bob(emerald) + shift;
+}
+
 static void Obj_EmeraldOrbitPlayer(mobj_t *emerald)
 {
-	const int kOrbitTics = 64;
-	const int kPhaseTics = 128;
-
-	const fixed_t orbit_radius = 100 * mapobjectscale;
-	const fixed_t orbit_height = 30 * mapobjectscale;
-
-	mobj_t *targ = emerald->target;
-
-	angle_t a = emerald->angle;
-
-	fixed_t x = FixedMul(orbit_radius, FCOS(a));
-	fixed_t y = FixedMul(orbit_radius, FSIN(a));
-
-	angle_t phase = (ANGLE_MAX / kPhaseTics) * (leveltime % kPhaseTics);
+	fixed_t r = get_current_radius(emerald);
+	fixed_t x = FixedMul(r, FCOS(emerald->angle));
+	fixed_t y = FixedMul(r, FSIN(emerald->angle));
 
 	P_MoveOrigin(
 			emerald,
-			targ->x + x,
-			targ->y + y,
-			targ->z + targ->height + FixedMul(orbit_height, FSIN(a + phase))
+			emerald->target->x + x,
+			emerald->target->y + y,
+			get_target_z(emerald)
 	);
 
-	emerald->angle += ANGLE_MAX / kOrbitTics;
+	emerald->angle += ANGLE_MAX / get_revolve_time(emerald);
 }
 
 void Obj_EmeraldThink(mobj_t *emerald)
@@ -84,3 +125,20 @@ void Obj_EmeraldThink(mobj_t *emerald)
 
 	K_BattleOvertimeKiller(emerald);
 }
+
+void Obj_BeginEmeraldOrbit(mobj_t *emerald, mobj_t *target, fixed_t radius, INT32 revolution_time)
+{
+	P_SetTarget(&emerald->target, target);
+
+	emerald_anim_start(emerald) = leveltime;
+	emerald_revolution_time(emerald) = revolution_time;
+
+	emerald_start_radius(emerald) = R_PointToDist2(target->x, target->y, emerald->x, emerald->y);
+	emerald_target_radius(emerald) = radius;
+
+	emerald->angle = R_PointToAngle2(target->x, target->y, emerald->x, emerald->y);
+	emerald_z_shift(emerald) = emerald->z - get_target_z(emerald);
+
+	emerald->flags |= MF_NOGRAVITY | MF_NOCLIP | MF_NOCLIPTHING | MF_NOCLIPHEIGHT;
+	emerald->shadowscale = 0;
+}
diff --git a/src/objects/ufo.c b/src/objects/ufo.c
index f8e15c459..0ed90df50 100644
--- a/src/objects/ufo.c
+++ b/src/objects/ufo.c
@@ -883,7 +883,7 @@ boolean Obj_UFOEmeraldCollect(mobj_t *ufo, mobj_t *toucher)
 		const int kScaleTics = 16;
 
 		// Emerald will now orbit the player
-		P_SetTarget(&emerald->target, toucher);
+		Obj_BeginEmeraldOrbit(emerald, toucher, 100 * mapobjectscale, 64);
 
 		// Scale down because the emerald is huge
 		// Super Emerald needs to be scaled down further