[Decompilation] [th01] Kikuri: Orb hitbox

ZUN *did* want a hitbox in the disc's horizontally centered upper half,
but then confused < and >, accidentally ending up with a hitbox from
the top of the playfield to the upper part of Kikuri's face instead… 🎺

Part of P0198, funded by Lmocinemod and Ember2528.

th01/main/boss/b15j.cpp

@@ -12,6 +12,7 @@ extern "C" {
 }
 #include "th01/formats/pf.hpp"
 #include "th01/math/area.hpp"
+#include "th01/math/overlap.hpp"
 #include "th01/math/subpixel.hpp"
 #include "th01/sprites/pellet.h"
 #include "th01/main/particle.hpp"
@@ -23,10 +24,29 @@ extern "C" {
 #include "th01/main/bullet/pellet.hpp"
 #include "th01/main/boss/boss.hpp"
 #include "th01/main/boss/entity_a.hpp"
+#include "th01/main/player/orb.hpp"
 
 // Coordinates
 // -----------
 
+static const screen_x_t DISC_CENTER_X = 320;
+static const screen_y_t DISC_CENTER_Y = 180;
+
+static const pixel_t HITBOX_W = 96;
+static const pixel_t HITBOX_H = 48;
+
+static const screen_x_t HITBOX_LEFT = (
+	DISC_CENTER_X - (HITBOX_W / 2) - (ORB_W / 2)
+);
+static const screen_x_t HITBOX_RIGHT = (
+	DISC_CENTER_X + (HITBOX_W / 2) - (ORB_W / 2)
+);
+
+// Not the actual Y coordinates of the original hitbox, due to a sign confusion
+// bug in kikuri_hittest_orb()!
+static const screen_y_t HITBOX_TOP = (DISC_CENTER_Y - HITBOX_H);
+static const screen_y_t HITBOX_BOTTOM = DISC_CENTER_Y;
+
 static const pixel_t SOUL_W = 32;
 static const pixel_t SOUL_H = 32;
 
@@ -169,3 +189,16 @@ void kikuri_free(void)
 	kikuri_ent_free();
 	kikuri_ptn_free();
 }
+
+bool16 near kikuri_hittest_orb(void)
+{
+	// Did you mean: > HITBOX_TOP? Using < describes a hitbox from the top of
+	// the playfield *until* that point instead...
+	if(
+		(orb_cur_left > HITBOX_LEFT) && (orb_cur_left < HITBOX_RIGHT) &&
+		(orb_cur_top < HITBOX_TOP) && (orb_cur_top < HITBOX_BOTTOM)
+	) {
+		return true;
+	}
+	return false;
+}

th01_reiiden.asm

@@ -14705,6 +14705,7 @@ main_34_TEXT	segment	byte public 'CODE' use16
 	extern @kikuri_select_for_rank$qmiiiii:proc
 	extern @kikuri_load$qv:proc
 	extern @kikuri_free$qv:proc
+	@kikuri_hittest_orb$qv procdesc near
 main_34_TEXT	ends
 
 main_34__TEXT	segment	byte public 'CODE' use16
@@ -14712,33 +14713,6 @@ main_34__TEXT	segment	byte public 'CODE' use16
 		;org 4
 		assume es:nothing, ss:nothing, ds:_DATA, fs:nothing, gs:nothing
 
-; =============== S U B	R O U T	I N E =======================================
-
-; Attributes: bp-based frame
-
-sub_235FD	proc near
-		push	bp
-		mov	bp, sp
-		cmp	_orb_cur_left, 256
-		jle	short loc_23625
-		cmp	_orb_cur_left, 352
-		jge	short loc_23625
-		cmp	_orb_cur_top, 132
-		jge	short loc_23625
-		cmp	_orb_cur_top, 180
-		jge	short loc_23625
-		mov	ax, 1
-		pop	bp
-		retn
-; ---------------------------------------------------------------------------
-
-loc_23625:
-		xor	ax, ax
-		pop	bp
-		retn
-sub_235FD	endp
-
-
 ; =============== S U B	R O U T	I N E =======================================
 
 ; Attributes: bp-based frame
@@ -16929,7 +16903,7 @@ loc_24B3E:
 		call	sub_23D19
 		pushd	0 or (0 shl 16)	; (hitbox_w) or (hitbox_h)
 		pushd	0 or (0 shl 16)	; (hitbox_left) or (hitbox_top)
-		call	sub_235FD
+		call	@kikuri_hittest_orb$qv
 		push	ax	; colliding_with_orb
 		push	seg main_32_TEXT	; hit_callback (segment)
 		push	offset @boss_nop$qv	; hit_callback (offset)
@@ -17013,7 +16987,7 @@ loc_24C2A:
 		mov	word_35D14, ax
 		pushd	0 or (0 shl 16)	; (hitbox_w) or (hitbox_h)
 		pushd	0 or (0 shl 16)	; (hitbox_left) or (hitbox_top)
-		call	sub_235FD
+		call	@kikuri_hittest_orb$qv
 		push	ax	; colliding_with_orb
 		push	seg main_32_TEXT	; hit_callback (segment)
 		push	offset @boss_nop$qv	; hit_callback (offset)
@@ -17051,7 +17025,7 @@ loc_24C81:
 		call	sub_240DE
 		pushd	0 or (0 shl 16)
 		pushd	0 or (0 shl 16)	; (hitbox_left) or (hitbox_top)
-		call	sub_235FD
+		call	@kikuri_hittest_orb$qv
 		push	ax	; colliding_with_orb
 		push	seg main_32_TEXT	; hit_callback (segment)
 		push	offset @boss_nop$qv	; hit_callback (offset)
@@ -17134,7 +17108,7 @@ loc_24D4C:
 loc_24D59:
 		pushd	0 or (0 shl 16)	; (hitbox_w) or (hitbox_h)
 		pushd	0 or (0 shl 16)	; (hitbox_left) or (hitbox_top)
-		call	sub_235FD
+		call	@kikuri_hittest_orb$qv
 		push	ax	; colliding_with_orb
 		push	seg main_32_TEXT	; hit_callback (segment)
 		push	offset @boss_nop$qv	; hit_callback (offset)