From 04fced3a60568ac3a862d90bcd6a3f2c5aa45dfc Mon Sep 17 00:00:00 2001
From: Lukas Krickl <lukas@krickl.dev>
Date: Thu, 13 Nov 2025 05:52:19 +0100
Subject: [PATCH] tiles: tile updates are now pre-computed

This saves a lot of time during vblank
---
 src/map.s   | 122 +++++++++++++++++++++++++++++++++-------------------
 src/tiles.s |   6 +--
 src/wram.s  |   2 +
 3 files changed, 81 insertions(+), 49 deletions(-)

diff --git a/src/map.s b/src/map.s
index 7ec22cb..0b8f553 100644
--- a/src/map.s
+++ b/src/map.s
@@ -137,57 +137,37 @@ map_tile_banks_load:
 	; draws a tile 
 	; to the screen
 	; inputs:
-	;   b/c: y/x position
+	;		update_tile_to_draw/vram: filled with valid ptr and tile data
 map_draw_tile:
-	; find tile to draw
-	push bc
-	call map_get_tile
-	ld bc, t_tile
-	add hl, bc ; hl = tile gfx
-	pop bc
-	
-	; load tile into a
-	ld a, [hl] ; a = tile
-	push af ; save tile gfx
+	; load vram destination
+	ld a, [update_tile_vram]
+	ld h, a
+	ld a, [update_tile_vram+1]
+	ld l, a
 
-	ld hl, SCRN0
-	ld de, MAP_W * 4  ; * 4 because tiles are 8x8 
+	ld de, update_tile_to_draw
 	
-	; skip y loop if b is 0
-	ld a, b
-	cp a, 0
-	jr z, @skip_y REL
-
-@y_loop:
-		add hl, de 
-		dec b
-		jr nz, @y_loop REL
-@skip_y:
-
-	ld d, 0
-	ld a, c
-	add a, a ; * 2 because tiles are 8x8
-	ld e, a
-	add hl, de ; hl = SCRN location
-		
-	pop af 
-
-	; draw 2x2 tile
+	; draw 4 tiles
+	ld a, [de]
+	inc de
 	ld [hl+], a
-	inc a
+	
+	ld a, [de]
+	inc de
 	ld [hl], a
 
+	; next row
 	; next row 
-	ld de, (MAP_W * 2) - 1
-	add hl, de
-	
-	; move down one tile row as well
-	add a, 15
+	ld bc, (MAP_W * 2) - 1
+	add hl, bc
 
+	ld a, [de]
+	inc de
 	ld [hl+], a
-	inc a
-	ld [hl], a
 
+	ld a, [de]
+	inc de
+	ld [hl], a
 	ret
 	
 	; gets a tile based on a position
@@ -228,13 +208,67 @@ map_get_tile:
 	; to tile_to_draw[0] to [3]
 	; inputs:
 	;		b/c: y/x position
+	;	returns:
+	;		update_tile_to_draw: 4 bytes of new tile data
+	;		upte_tile_vram: ptr to vram
 map_draw_tile_prep:
+	; find tile to draw
+	push bc
 	call map_get_tile
-	; hl = tile
+	ld bc, t_tile
+	add hl, bc ; hl = tile gfx
+	pop bc
 	
-	ld de, update_tile_to_draw
+	; load tile into a
+	ld a, [hl] ; a = tile
+	push af ; save tile gfx
+
+	ld hl, SCRN0
+	ld de, MAP_W * 4  ; * 4 because tiles are 8x8 
+	
+	; skip y loop if b is 0
+	ld a, b
+	cp a, 0
+	jr z, @skip_y REL
+
+@y_loop:
+		add hl, de 
+		dec b
+		jr nz, @y_loop REL
+@skip_y:
+
+	ld d, 0
+	ld a, c
+	add a, a ; * 2 because tiles are 8x8
+	ld e, a
+	add hl, de ; hl = SCRN location
+
+	; save hl to vram ptr 
+
+	ld a, h
+	ld [update_tile_vram], a
+	ld a, l
+	ld [update_tile_vram+1], a
+	
+	; hl = tile data buffer
+	ld hl, update_tile_to_draw
+
+	; a = start tile
+	pop af 
+
+	; draw 2x2 tile
+	ld [hl+], a
+	inc a
+	ld [hl+], a
+
+	
+	; move down one tile row as well
+	add a, 15
+
+	ld [hl+], a
+	inc a
+	ld [hl], a
 
-	; TODO:
 	ret
 
 #macro map_draw_row_inc_c
diff --git a/src/tiles.s b/src/tiles.s
index 996c325..af25ea8 100644
--- a/src/tiles.s
+++ b/src/tiles.s
@@ -76,12 +76,8 @@ tile_update_selected:
 	ret
 	
 	; draws the recently updated tile
-	; bsed on update_tile y and x
+	; based on update_tile prep set in previous frame
 tile_update_draw:
-	ld a, [update_tile_y]
-	ld b, a
-	ld a, [update_tile_x]
-	ld c, a
 	jp map_draw_tile
 
 
diff --git a/src/wram.s b/src/wram.s
index ec8ce4a..f5a454b 100644
--- a/src/wram.s
+++ b/src/wram.s
@@ -106,3 +106,5 @@ update_tile: .adv 2
 	; that represent the current tile
 	; this gets drawn during the next blank
 update_tile_to_draw: .adv 4
+	; ptr to vram for the next update tile
+update_tile_vram: .adv 2
-- 
2.30.2