From e2564ecedc4dbe9bad5536c22ce3709fef50499b Mon Sep 17 00:00:00 2001
From: Forest Belton <65484+forestbelton@users.noreply.github.com>
Date: Sat, 17 Jul 2021 01:00:16 -0400
Subject: [PATCH] Update collision for new map engine

---
 src/collision.s | 109 +++++++++++++++++++++++++++++++-----------------
 1 file changed, 70 insertions(+), 39 deletions(-)

diff --git a/src/collision.s b/src/collision.s
index ab9a511..eeea510 100644
--- a/src/collision.s
+++ b/src/collision.s
@@ -3,34 +3,54 @@ INCLUDE "oam.inc"
 SECTION "Collision", ROM0
 
 ; Determines if player has hit the background
-; @return NZ = false, Z = true
+; @return NZ = true, Z = false
 player_bg_collides::
-    ; c = x % 8 == 0 ? x/8 : x/8 + 1
+    ; C = MAP X = PLAYER X / 8 + CAMERA X
     ld a, [PLAYER_X]
+    call get_tile_coord
     ld c, a
-    and %111
-    jr z, .skip_inc_c
-    ld a, c
-    add 8
+
+    ld a, [CURRENT_CAMERA_X]
+    add c
     ld c, a
-.skip_inc_c:
-    srl c
-    srl c
-    srl c
 
-    ; b = y % 8 == 0 ? y/8 : y/8 + 1
+    ; C < 0
+    bit 7, c
+    ret nz
+
+    ; C >= MAP WIDTH
+    ld a, [CURRENT_MAP_WIDTH]
+    cp c
+    jr nz, .load_y
+
+    ; Set NZ
+    or $ff
+    ret
+
+.load_y:
+    ; B = MAP Y = PLAYER Y / 8 + CAMERA Y
     ld a, [PLAYER_Y]
+    call get_tile_coord
     ld b, a
-    and %111
-    jr z, .skip_inc_b
-    ld a, b
-    add 8
+
+    ld a, [CURRENT_CAMERA_Y]
+    add b
     ld b, a
-.skip_inc_b:
-    srl b
-    srl b
-    srl b
 
+    ; B < 0
+    bit 7, b
+    ret nz
+
+    ; B >= MAP HEIGHT
+    ld a, [CURRENT_MAP_HEIGHT]
+    cp b
+    jr nz, .check_tiles
+
+    ; Set NZ
+    or $ff
+    ret
+
+.check_tiles:
     ; top left
     call can_move_to
     ret nz
@@ -57,29 +77,20 @@ player_bg_collides::
 player_in_air::
     ; c = x % 8 == 0 ? x/8 : x/8 + 1
     ld a, [PLAYER_X]
+    call get_tile_coord
     ld c, a
-    and %111
-    jr z, .skip_inc_c
-    ld a, c
-    add 8
+
+    ld a, [CURRENT_CAMERA_X]
+    add c
     ld c, a
-.skip_inc_c:
-    srl c
-    srl c
-    srl c
 
-    ; b = y % 8 == 0 ? y/8 : y/8 + 1
     ld a, [PLAYER_Y]
+    call get_tile_coord
     ld b, a
-    and %111
-    jr z, .skip_inc_b
-    ld a, b
-    add 8
+
+    ld a, [CURRENT_CAMERA_Y]
+    add b
     ld b, a
-.skip_inc_b:
-    srl b
-    srl b
-    srl b
 
     ; check underneath player (2 tiles down from top-left sprite)
     inc b
@@ -99,14 +110,13 @@ player_in_air::
 ; @destroy a, d, e
 ; @note NZ = false, Z = true
 can_move_to:
-    ; todo: should be aware of scx/scy
     push bc
     push hl
 
     ld a, [CURRENT_MAP_COLLISION]
-    ld h, a
-    ld a, [CURRENT_MAP_COLLISION + 1]
     ld l, a
+    ld a, [CURRENT_MAP_COLLISION + 1]
+    ld h, a
 
     ld a, [CURRENT_MAP_WIDTH]
     ld d, 0
@@ -127,3 +137,24 @@ can_move_to:
     pop bc
 
     ret
+
+; Convert from pixel space to tile space
+; @param a Screen pixel coordinate
+; @destroys hl
+; @returns Screen tile coordinate in A
+get_tile_coord:
+    ld hl, sp - 1
+    ld [hl], a
+
+    and %111
+    ld a, [hl]
+
+    jr z, .skip_inc
+    add 8
+
+.skip_inc:
+    srl a
+    srl a
+    srl a
+
+    ret