Fix for Epona spawning when entering scene on water

ASM/c/player.h

@@ -0,0 +1,6 @@
+#ifndef PLAYER_H
+#define PLAYER_H
+
+extern int16_t R_EXITED_SCENE_RIDING_HORSE;
+
+#endif

ASM/c/z64.h

@@ -139,6 +139,11 @@ typedef struct {
   z64_col_water_t  *water;
 } z64_col_hdr_t;
 
+typedef struct {
+    /* 0x00 */ z64_col_hdr_t* colHeader; // scene's static collision
+    /* 0x04 */ char colCtxData[0x1460];
+} CollisionContext;
+
 typedef enum {
   Z64_ITEM_NULL = -1,
   Z64_ITEM_STICK,
@@ -1394,8 +1399,7 @@ typedef struct {
   char             unk_07_[0x0010];        /* 0x00798 */
   z64_lighting_t   lighting;               /* 0x007A8 */
   char             unk_08_[0x0008];        /* 0x007B8 */
-  z64_col_hdr_t   *col_hdr;                /* 0x007C0 */
-  char             unk_09_[0x1460];        /* 0x007C4 */
+  CollisionContext colCtx;                 /* 0x007C0 */
   z64_actor_ctxt_t actor_ctxt;             /* 0x01C24 */
   uint8_t          n_actors_loaded;        /* 0x01C2C */
   char             unk_0A_[0x0003];        /* 0x01C2D */

ASM/c/z_player.c

@@ -0,0 +1,47 @@
+#include "z64.h"
+#include "actor.h"
+#include "player.h"
+
+#define SCENE_HYRULE_FIELD      0x51
+#define SCENE_LAKE_HYLIA        0x57
+#define SCENE_GERUDO_VALLEY     0x5A
+#define SCENE_GERUDOS_FORTRESS  0x5D
+#define SCENE_LON_LON_RANCH     0x63
+
+extern int32_t BgCheck_AnyLineTest1(CollisionContext* colCtx, z64_xyzf_t* posA, z64_xyzf_t* posB,
+                                    z64_xyzf_t* posResult, z64_col_poly_t** outPoly, int32_t chkOneFace);
+
+/**
+ * Do a line intersect test between player position and waterbox surface Y position
+ * If resulting Y position is less than or equal to waterbox surface, player is either
+ * in water (eg. Zora's River water- > Hyrule Field) or directly above water surface
+ * (Gerudo Valley -> Lake Hylia), so should not spawn Epona.
+ * float ySurface is $f12 = (waterbox Y surface - player Y position)
+ */
+void Player_CheckEponaWater(volatile float ySurface) {
+    // Exited riding into an Epona allowed scene
+    if(R_EXITED_SCENE_RIDING_HORSE == true &&
+        (z64_game.scene_index == SCENE_HYRULE_FIELD || z64_game.scene_index == SCENE_LAKE_HYLIA ||
+        z64_game.scene_index == SCENE_GERUDO_VALLEY || z64_game.scene_index == SCENE_GERUDOS_FORTRESS ||
+        z64_game.scene_index == SCENE_LON_LON_RANCH)) {
+
+        z64_col_poly_t* floorPoly;
+        z64_xyzf_t pos = (z64_xyzf_t){z64_link.common.pos_world.x, ySurface, z64_link.common.pos_world.z};
+        z64_xyzf_t posResult;
+
+        // Check line intersection: player position vs player-waterbox Y position "pos"
+        // Intersect position is stored in "posResult"
+        BgCheck_AnyLineTest1(&z64_game.colCtx, &z64_link.common.pos_world, &pos, &posResult, &floorPoly, false);
+
+        // If the water surface is either higher than resulting Y position (= is above floor),
+        // or same height (= is waterbox itself), water is higher than the floor
+        if((posResult.y <= ySurface)) {
+            // Dismount in all areas, except Lake Hylia warp entrance (X pos -1045).
+            // (That waterbox has Y surface -90 for one frame, so special X-based fix is needed)
+            if((z64_game.scene_index != SCENE_LAKE_HYLIA) || (z64_game.scene_index == SCENE_LAKE_HYLIA &&
+            !(z64_link.common.pos_world.x > -1050.0f && z64_link.common.pos_world.x < -1040.0f))) {
+                R_EXITED_SCENE_RIDING_HORSE = false;
+            }
+        }
+    }
+}

ASM/ootSymbols.ld

@@ -17,6 +17,7 @@ Flags_UnsetTempClear = 0x800206C8;
 Flags_GetCollectible = 0x800206E8;
 Flags_SetCollectible = 0x8002071C;
 Actor_SetColorFilter = 0x80027090;
+BgCheck_AnyLineTest1 = 0x80030ae8;
 CutsceneFlags_Get = 0x8005991C;
 z64_Gfx_SetupDL_42Opa = 0x8007E868;
 Audio_StopCurrentMusic = 0x800C7684;
@@ -27,6 +28,7 @@ z64_ItemIcons = 0x800F8D2C;
 z64_SfxDefaultPos = 0x80104394;
 z64_SfxDefaultFreqAndVolScale = 0x801043A0;
 z64_SfxDefaultReverb = 0x801043A8;
+R_EXITED_SCENE_RIDING_HORSE = 0x801c7cf0;
 KaleidoScope_DrawAmmoCount = 0x8038EA10;
 KaleidoScope_SetCursorVtx = 0x8038EF94;
 KaleidoScope_QuadTextureIA8 = 0x80394200;

ASM/src/build.asm

@@ -133,6 +133,7 @@ RANDO_CONTEXT:
 .include "en_dns.asm"
 .include "bg_gate_shutter.asm"
 .include "big_poe.asm"
+.include "player_callcheckeponawater.asm"
 
 .align 0x10
 .importobj "../build/bundle.o"

ASM/src/hacks.asm

@@ -4161,3 +4161,4 @@ DemoEffect_DrawJewel_AfterHook:
 .include "hacks/ovl_en_ssh.asm"
 .include "hacks/ovl_en_okarina_tag.asm"
 .include "hacks/sound.asm"
+.include "hacks/z_player.asm"

ASM/src/hacks/z_player.asm

@@ -0,0 +1,14 @@
+.headersize(0x808301c0 - 0xbcdb70)
+
+;================================================================================
+; Fixes Epona spawning on water when exiting into a water entrance while riding.
+;================================================================================
+; Replaces      sub.s   $f10,$f6,$f8
+;               move    a0,s1
+;               move    a1,s0
+;               swc1    $f10,40(sp)
+.org 0x8083aa1c                     ; in Player_SetStartingMovement (start at 0x80393360)
+    sub.s   $f12,$f6,$f8            ; (waterbox Y surface - player Y) = ySurface
+    move    s7,a2                   ; store Player_Action_StartModeWater address
+    jal     Player_CallCheckEponaWater
+    swc1    $f12,40(sp)             ; store new ySurface (restored in end of jal to $f10)

ASM/src/player_callcheckeponawater.asm

@@ -0,0 +1,12 @@
+Player_CallCheckEponaWater:
+    addiu   sp,sp,-24
+    sw      ra,16(sp)
+    jal     Player_CheckEponaWater
+    nop
+    lw      ra,16(sp)
+    addiu   sp,sp,24
+    move    a0,s1
+    move    a1,s0       ; Restore displaced a0 and a1 (z64_game and z64_link),
+    move    a2,s7       ; address to Player_Action_StartModeWater to a2,
+    jr      ra
+    lwc1    $f10,40(sp) ; and ySurface as $f10 (for c.le.s after return)