From 7c2792139465a82edef76380278d109653f70353 Mon Sep 17 00:00:00 2001
From: Vince Weaver <vincent.weaver@maine.edu>
Date: Wed, 2 Feb 2022 15:12:54 -0500
Subject: [PATCH] orb: down to 252 bytes!

---
 demos/l/orb_256/combo.s     |  9 +++++++--
 demos/l/orb_256/orb.s       | 28 +++++++++++++++-------------
 demos/l/orb_256/staggered.s | 20 +++++++++++---------
 3 files changed, 33 insertions(+), 24 deletions(-)

diff --git a/demos/l/orb_256/combo.s b/demos/l/orb_256/combo.s
index fdcd69c9..72365409 100644
--- a/demos/l/orb_256/combo.s
+++ b/demos/l/orb_256/combo.s
@@ -11,11 +11,14 @@
 ; 263 bytes -- more circle optimization
 ; 261 bytes -- optimize boxes
 ; 257 bytes -- optimize staggered
+; 255 bytes -- put some circle draw code in loop
+; 253 bytes -- reuse previous zeroed ZP address for the staggered code
+; 252 bytes -- trying removing random SEC to see if it hurts things
 
 ; zero page
 
-GBASL		= $26
-GBASH		= $27
+;GBASL		= $26
+;GBASH		= $27
 ; D0+ used by HGR routines
 HGR_COLOR	= $E4
 HGR_PAGE	= $E6
@@ -28,6 +31,8 @@ X1              = $F3
 COLOR           = $F4
 
 COUNT		= $F6
+INDEXL		= $F6
+INDEXH		= $F7
 
 XX		= $F7
 MINUSXX		= $F8
diff --git a/demos/l/orb_256/orb.s b/demos/l/orb_256/orb.s
index c49af65f..14db0fbf 100644
--- a/demos/l/orb_256/orb.s
+++ b/demos/l/orb_256/orb.s
@@ -33,6 +33,8 @@ draw_next:
 	sbc	R
 	sbc	R
 
+	; D is now in A
+
 	; always odd, never zero
 
 	bne	do_plots		; bra	skip ahead first time through
@@ -53,7 +55,7 @@ d_positive:
 	; D=D+4*(XX-YY)+10
 
 	; XX is already in A
-	sec
+;	sec				; saves a byte, seems to be OK?
 	sbc	YY
 	ldy	#10
 d_negative:
@@ -71,17 +73,17 @@ do_plots:
 
 	sta	D
 
-	; setup constants
+	; setup plus/minus XX/YY
 
-	lda	XX
+	ldx	#2
+plus_minus_loop:
+	lda	XX,X
 	eor	#$FF
-	sta	MINUSXX
-	inc	MINUSXX
-
-	lda	YY
-	eor	#$FF
-	sta	MINUSYY
-	inc	MINUSYY
+	sta	MINUSXX,X
+	inc	MINUSXX,X
+	dex
+	dex
+	bpl	plus_minus_loop
 
 	; HPLOT CX+X,CY+Y
 	; HPLOT CX-X,CY+Y
@@ -106,7 +108,7 @@ pos_loop:
 	lda	#96			; center around y=96
 	clc
 	adc	XX,X			; index with COUNT
-	pha				; save for later
+	tay				; save for later
 
 	; calc x co-ord
 
@@ -121,7 +123,7 @@ pos_loop:
 
 	tax
 
-	pla			; restore Y co-ordinate
+	tya			; restore Y co-ordinate
 	ldy	#0		; always 0
 
 	jsr	HPLOT0		; plot at (Y,X), (A)
@@ -148,7 +150,7 @@ pos_loop:
 
 	; IF YY>=XX THEN 4
 	; should be equivelant to IF XX<YY
-	; but sadly appears we need IF XX<=YY for same effect
+	; but sadly appears we need IF XX<=YY for our initial effect
 	lda	YY
 	cmp	XX
 	bcs	circle_loop
diff --git a/demos/l/orb_256/staggered.s b/demos/l/orb_256/staggered.s
index 2fe5f13b..7501b7ad 100644
--- a/demos/l/orb_256/staggered.s
+++ b/demos/l/orb_256/staggered.s
@@ -5,33 +5,35 @@ staggered:
 	stx	FRAME				; set FRAME to 48
 
 	ldx	#$00				; init X to 0
-	stx	GBASL				; set GBASL to 0
+	; we can count on INDEXL (COUNT) being 0 from the orb code
+;	stx	INDEXL				; set INDEXL to 0
 
 	; pulse loop horizontal
 outer_loop:
-	lda	#$40				; reset GBASH to begin page2
-	sta	GBASH
+	lda	#$40				; reset INDEXH to begin page2
+	sta	INDEXH
 
 inner_loop:
 	lda	even_lookup,X			; get even color
-	sta	(GBASL),Y			; store it to memory
+	sta	(INDEXL),Y			; store it to memory
 	iny
 
 	lda	odd_lookup,X			; get odd color
-	sta	(GBASL),Y			; store it to memory
+	sta	(INDEXL),Y			; store it to memory
 	iny
 
 	bne	inner_loop			; repeat for 256
 
-	inc	GBASH				; point to next page
+	inc	INDEXH				; point to next page
 
-	inx					; wrap lookup at 8
-	txa
+	inx					; point to next lookup
+
+	txa					; wrap to 0..7
 	and	#$7
 	tax
 
 	lda	#$60				; see if done
-	cmp	GBASH
+	cmp	INDEXH
 	bne	inner_loop
 
 ;	lda	#100				; A is $60 here