From 67fb9aa9a6f2b19f2eb354a1def86d6ca084dab9 Mon Sep 17 00:00:00 2001
From: Lukas Krickl <lukas@krickl.dev>
Date: Mon, 8 Sep 2025 17:18:46 +0200
Subject: [PATCH] animation: Added actor runtime tile offsets

---
 src/animation.s | 96 +++++++++++++++++++++++++++++++++++++++++++++++--
 src/defs.s      | 12 +++++++
 src/macros.inc  |  2 ++
 src/unit.s      | 80 -----------------------------------------
 4 files changed, 107 insertions(+), 83 deletions(-)

diff --git a/src/animation.s b/src/animation.s
index 176e29d..d85e40c 100644
--- a/src/animation.s
+++ b/src/animation.s
@@ -1,3 +1,93 @@
-; animation tables
-; each actor type has a table of all frames
-; of animation it may have
+
+
+  ; calls unit's draw function
+  ; inputs:
+  ;   hl: actor ptr
+unit_update_draw:
+  push hl
+  ld de, act_draw
+  add hl, de
+  ; hl = draw ptr
+  ld a, [hl+]
+  ld e, a
+  ld a, [hl]
+  ld d, a
+  ; de = draw function
+  push de
+  pop hl ; hl = draw function
+  pop de ; de = actor
+  call_hl
+  ret
+
+  ; gets the left tile offset
+  ; for object 1
+  ; based on the y flip of oam
+  ; inputs:
+  ;   a: oam flags
+  ; returns:
+  ;   a: x-offset
+get_left_tile_offset1:
+  and a, OAM_FXFLIP 
+  jr z, @not_set REL
+  ld a, 8
+  ret
+@not_set:
+  xor a, a
+  ret 
+
+  ; gets the left tile offset
+  ; for object 2
+  ; based on the y flip of oam
+  ; inputs:
+  ;   a: oam flags
+  ; returns:
+  ;   a: x-offset
+get_left_tile_offset2:
+  and a, OAM_FXFLIP 
+  jr z, @not_set REL
+  xor a, a
+  ret
+@not_set:
+  ld a, 8
+  ret
+	
+	; draws the unit's tile
+	; based on the set oam tile 
+	; and the currently set offset 
+	; each actor has 2 tiles drawn here
+	; tile 1 is the selected tile
+	; tile 2 is the tile next (+1) to the selected tile
+  ; inputs
+  ;   de: actor
+unit_draw:
+  push de
+  ld hl, act_oam_tile
+  add hl, de ; hl = tile 
+  ld a, [hl+]
+
+  ld b, a ; base tile
+  ld a, [hl+]
+  ld c, a ; flags
+	ld a, [hl] ; a = tile offset
+	BREAK
+	add a, b ; base tile + offset
+	ld b, a ; b = real tile
+
+	ld a, c ; c = oam flags for offset call
+  call get_left_tile_offset1
+  push bc
+  call unit_generic_draw
+  
+  ; draw same tile again 
+  pop bc
+  pop de
+  push de
+  inc b  
+  inc b ; b+=2
+  ld a, c ; a = flags
+  call get_left_tile_offset2
+  call unit_generic_draw 
+  pop de
+
+  ldnull bc
+  ret
diff --git a/src/defs.s b/src/defs.s
index 046d450..b004e4c 100644
--- a/src/defs.s
+++ b/src/defs.s
@@ -238,6 +238,18 @@
   ;   tile table. This can be implemented as needed
 .de act_oam_tile, 1
 .de act_oam_flags, 1
+	
+	; offset from the currently selected tile
+	; animations work by applying this offset
+	; to the selected base tile
+	; this allows runtime configuration
+	; of the frames
+	; e.g. the offset could be switched to 0/2 based 
+	; on the current frame count
+	; to make an idel animation
+	; note: the offset should always be an even number
+	; due to the use of 8x16 objects
+.de act_rt_oam_tile_offset, 1
   
 .de act_size, 0
   
diff --git a/src/macros.inc b/src/macros.inc
index 2cfc7ed..7ad9c98 100644
--- a/src/macros.inc
+++ b/src/macros.inc
@@ -163,6 +163,8 @@
   dw $1
   .db $2
   .db $3
+	; tile offset
+	.db 0 
 #endmacro
 
   ; define an actor without state
diff --git a/src/unit.s b/src/unit.s
index 451d710..a64eff7 100644
--- a/src/unit.s
+++ b/src/unit.s
@@ -46,86 +46,6 @@ units_update:
 
   ret
 
-  ; calls unit's draw function
-  ; inputs:
-  ;   hl: actor ptr
-unit_update_draw:
-  push hl
-  ld de, act_draw
-  add hl, de
-  ; hl = draw ptr
-  ld a, [hl+]
-  ld e, a
-  ld a, [hl]
-  ld d, a
-  ; de = draw function
-  push de
-  pop hl ; hl = draw function
-  pop de ; de = actor
-  call_hl
-  ret
-
-  ; gets the left tile offset
-  ; for object 1
-  ; based on the y flip of oam
-  ; inputs:
-  ;   a: oam flags
-  ; returns:
-  ;   a: x-offset
-get_left_tile_offset1:
-  and a, OAM_FXFLIP 
-  jr z, @not_set REL
-  ld a, 8
-  ret
-@not_set:
-  xor a, a
-  ret 
-
-  ; gets the left tile offset
-  ; for object 2
-  ; based on the y flip of oam
-  ; inputs:
-  ;   a: oam flags
-  ; returns:
-  ;   a: x-offset
-get_left_tile_offset2:
-  and a, OAM_FXFLIP 
-  jr z, @not_set REL
-  xor a, a
-  ret
-@not_set:
-  ld a, 8
-  ret
-
-  ; inputs
-  ;   de: actor
-unit_draw:
-  push de
-  ld hl, act_oam_tile
-  add hl, de ; hl = tile 
-  ld a, [hl+]
-
-  ld b, a ; tile
-  ld a, [hl]
-  ld c, a ; flags
-  call get_left_tile_offset1
-  push bc
-  call unit_generic_draw
-  
-  ; draw same tile again 
-  pop bc
-  pop de
-  push de
-  inc b  
-  inc b ; b+=2
-  ld a, c ; a = flags
-  call get_left_tile_offset2
-  call unit_generic_draw 
-  pop de
-
-  ldnull bc
-  ret
-
   ; adjust an object's position 
   ; based on sub-tile state
   ; inputs:
-- 
2.30.2