From ca551c1700cf982fe96388491a096b515365894f Mon Sep 17 00:00:00 2001
From: "Juan J. Martinez" <jjm@usebox.net>
Date: Fri, 5 May 2023 21:39:32 +0100
Subject: Use the MSB of the index to mark a transparent color

Because we use 1 byte to store 4bpp, we don't need a mask and we can
encode a "transparent" color  in the bits we don't use.
---
 example.asm | 9 +++++++++
 1 file changed, 9 insertions(+)

(limited to 'example.asm')

diff --git a/example.asm b/example.asm
index 73aa9a5..2ab0ee7 100644
--- a/example.asm
+++ b/example.asm
@@ -75,7 +75,16 @@ draw_sprite:
 line:
     push x
     ld x, [a : x]
+
+    ; any color with index > 15
+    ; is transparent
+    cmp x, 16
+    bnc
+    jmp transparent
+
     ld [b : y], x
+
+transparent:
     pop x
 
     inc x
-- 
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