From e4183cdb16f93005e6fe930ccd4613bae8a83e3b Mon Sep 17 00:00:00 2001
From: John Tsiombikas <nuclear@member.fsf.org>
Date: Thu, 15 Sep 2022 12:06:41 +0300
Subject: [PATCH] fixed pixel order, added LARGE option

---
 xortest.s |   40 ++++++++++++++++++++++++++++++----------
 1 file changed, 30 insertions(+), 10 deletions(-)

diff --git a/xortest.s b/xortest.s
index ce89274..9a32dc2 100644
--- a/xortest.s
+++ b/xortest.s
@@ -1,5 +1,7 @@
 	org $800
 
+LARGE = 0
+
 REG_NEWVID = $c029
 FB_BASE	= $e12000
 
@@ -12,7 +14,7 @@ FB_BASE	= $e12000
 	rep #$30	; accum/index 16bit
 	lda #$0000
 	ldx #$0000
-fillrest
+fillrest		; @30f
 	stal $e19d00,x
 	inx
 	inx
@@ -20,7 +22,7 @@ fillrest
 	bne fillrest
 	
 	lda #$0000
-cmap	pha
+cmap	pha		; @31d
 	sta 0
 	asl
 	tax	; offset = i * 2
@@ -39,23 +41,41 @@ cmap	pha
 
 YVAL	= 0
 TMPVAL	= 1
+YNIB	= 2
 
-	sep #$20	; accum 8bit
-	ldx #0		; fb index
+	sep #$20	; accum 8bit  @337
+	ldx #0000	; fb index
 	stz YVAL
-yloop	ldy #0000	; column/2 on Y reg
-xloop	tya
+yloop	ldy #0000	; column/2 on Y reg  @33e
+xloop	lda YVAL	; @341
+
+	DO LARGE
+	lsr
+	FIN
+
+	and #$0f
+	sta YNIB
+	tya
+
+	DO LARGE = 0
 	asl
+	inc		; increment X, next pixel on low nibble
+	FIN
+
 	and #$0f
 	sta TMPVAL	; save first pixel X coordinate
-	inc		; increment by 1 for the next pixel
-	eor YVAL
+
+	DO LARGE = 0
+	dec		; decrement back for high nibble pixel
+	FIN
+
+	eor YNIB
 	asl		; move next pixel value to high nibble
 	asl
 	asl
 	asl
 	ora TMPVAL	; first pixel X -> low nibble
-	eor YVAL
+	eor YNIB
 
 	stal FB_BASE, x	; write the pixel pair
 	inx
@@ -67,6 +87,6 @@ xloop	tya
 	cmp #200
 	bne yloop
 
-infloop	bra infloop
+infloop	bra infloop	; @36d
 
 	; vi:ft=asm_ca65
-- 
1.7.10.4