From 627e526d0a4631f6a65ca18ee6fdad5e0c51e24a Mon Sep 17 00:00:00 2001
From: "Juan J. Martinez" <jjm@usebox.net>
Date: Sat, 6 May 2023 19:35:19 +0100
Subject: Improve comments and refactored turn

---
 example.asm | 53 +++++++++++++++++++++++++----------------------------
 1 file changed, 25 insertions(+), 28 deletions(-)

diff --git a/example.asm b/example.asm
index 48ee7db..6714543 100644
--- a/example.asm
+++ b/example.asm
@@ -46,21 +46,9 @@ loop:
     jmp update_y
 
 turn_x:
-    ; update incx
-    ;  1 -> -1
-    ; -1 -> 1
     ld a, >incx
     ld x, <incx
-    ld y, [a : x]
-    ld b, 254
-    xor y, b
-    ld [a : x], y
-
-    ; change color
-    pop b
-    inc b
-    and b, 15
-    push b
+    call turn
 
 update_y:
     ld a, >incy
@@ -83,21 +71,9 @@ update_y:
     jmp update_done
 
 turn_y:
-    ; update incy
-    ;  1 -> -1
-    ; -1 -> 1
     ld a, >incy
     ld x, <incy
-    ld y, [a : x]
-    ld b, 254
-    xor y, b
-    ld [a : x], y
-
-    ; change color
-    pop b
-    inc b
-    and b, 15
-    push b
+    call turn
 
 update_done:
 
@@ -109,7 +85,26 @@ update_done:
     pop b
     jmp loop
 
-    ; fill frame-buffer with a color in reg b
+    ; make the sprite change direction
+    ; in: [a : x] inc*
+turn:
+    ;  1 -> -1
+    ; -1 -> 1
+    ld y, [a : x]
+    ld b, 254
+    xor y, b
+    ld [a : x], y
+
+    ; change color
+    ld b, [sp + 2]
+    inc b
+    and b, 15
+    ld [sp + 2], b
+    ret
+
+
+    ; fill frame-buffer
+    ; in: reg b color
 fill_screen:
     ld a, 0xbf
     ld x, 0
@@ -128,7 +123,8 @@ fill_loop:
 int_handler:
     iret
 
-    ; draw sprite getting coordinates from px, py
+    ; draw sprite
+    ; in: coordinates in px, py
 draw_sprite:
     ; blitter in settings mode
     ld x, 128
@@ -142,6 +138,7 @@ draw_sprite:
     port a, x
     ld x, >sprite
     port a, x
+    ; destination
     ld y, <px
     ld b, >px
     ld x, [b : y]
-- 
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