From 89d706cb0efbbcf428b01843dc0555cab0fd3f9c Mon Sep 17 00:00:00 2001
From: Vince Weaver <vince@deater.net>
Date: Sun, 28 Mar 2021 18:04:19 -0400
Subject: [PATCH] graphics: lines: look into recursive

---
 graphics/gr/lines/Makefile        |  13 ++-
 graphics/gr/lines/lines_recurse.s | 138 ++++++++++++++++++++++++++++++
 2 files changed, 149 insertions(+), 2 deletions(-)
 create mode 100644 graphics/gr/lines/lines_recurse.s

diff --git a/graphics/gr/lines/Makefile b/graphics/gr/lines/Makefile
index 84575fff..8a2dddee 100644
--- a/graphics/gr/lines/Makefile
+++ b/graphics/gr/lines/Makefile
@@ -7,7 +7,7 @@ EMPTYDISK = ../../../empty_disk/empty.dsk
 
 all:	lines.dsk
 
-lines.dsk:	HELLO LINES LINES_SMALL LINES_ROM LINES_WIKI LINES_BOT
+lines.dsk:	HELLO LINES LINES_SMALL LINES_ROM LINES_WIKI LINES_BOT LINES_RECURSE
 	cp $(EMPTYDISK) lines.dsk
 	$(DOS33) -y lines.dsk SAVE A HELLO
 	$(DOS33) -y lines.dsk BSAVE -a 0xC00 LINES
@@ -15,6 +15,7 @@ lines.dsk:	HELLO LINES LINES_SMALL LINES_ROM LINES_WIKI LINES_BOT
 	$(DOS33) -y lines.dsk BSAVE -a 0xC00 LINES_ROM
 	$(DOS33) -y lines.dsk BSAVE -a 0xC00 LINES_WIKI
 	$(DOS33) -y lines.dsk BSAVE -a 0x36B LINES_BOT
+	$(DOS33) -y lines.dsk BSAVE -a 0xC00 LINES_RECURSE
 
 ###
 
@@ -55,6 +56,14 @@ lines_wiki.o:	lines_wiki.s
 
 ###
 
+LINES_RECURSE:	lines_recurse.o
+	ld65 -o LINES_RECURSE lines_recurse.o -C $(LINKERSCRIPTS)/apple2_c00.inc
+
+lines_recurse.o:	lines_recurse.s
+	ca65 -o lines_recurse.o lines_recurse.s -l lines_recurse.lst
+
+###
+
 LINES_BOT:	lines_bot.o
 	ld65 -o LINES_BOT lines_bot.o -C ./apple2_36b.inc
 
@@ -64,4 +73,4 @@ lines_bot.o:	lines_bot.s
 ###
 
 clean:	
-	rm -f *~ *.o *.lst HELLO LINES LINES_SMALL LINES_ROM LINES_WIKI LINES_BOT
+	rm -f *~ *.o *.lst HELLO LINES LINES_SMALL LINES_ROM LINES_WIKI LINES_BOT LINES_RECURSE
diff --git a/graphics/gr/lines/lines_recurse.s b/graphics/gr/lines/lines_recurse.s
new file mode 100644
index 00000000..7b2aed89
--- /dev/null
+++ b/graphics/gr/lines/lines_recurse.s
@@ -0,0 +1,138 @@
+; Bresenham Lines
+
+; by Vince `deater` Weaver <vince@deater.net>
+
+; http://www.retroprogramming.com/2016/05/divide-and-conquer-line-algorithm-for.html
+
+.include "zp.inc"
+.include "hardware.inc"
+
+B_X1	= $F0
+B_Y1	= $F1
+B_X2	= $F2
+B_Y2	= $F3
+COUNT	= $F9
+
+X1	=	$1000
+Y1	=	$1100
+X2	=	$1200
+Y2	=	$1300
+MIDX	=	$1400
+MIDY	=	$1500
+
+lines:
+
+	jsr	SETGR		; set lo-res 40x40 mode
+				; A=$D0 afterward
+
+restart:
+	lda	#0
+	sta	COUNT
+lines_loop:
+
+	jsr	NEXTCOL
+
+	lda	#0
+	sta	X1
+	lda	#36
+	sta	Y2
+
+	lda	COUNT
+	cmp	#10
+;end:
+	beq	restart
+
+	asl
+	asl
+	sta	Y1
+	sta	X2
+
+	jsr	draw_line
+
+	inc	COUNT
+
+	jmp	lines_loop
+
+
+
+	;============================
+	; draw line
+	;	from x1,y1 to x2,y2
+	;============================
+draw_line:
+	ldx	#0
+draw_recurse:
+
+;int draw ( ax, ay, bx, by )
+;{
+;    int midx, midy;
+;    midx = ( ax+bx ) / 2;
+;    midy = ( ay+by ) / 2;
+;    if ( midx != ax && midy != ay )
+;    {
+;        draw( midx, midy, ax, ay );
+;        draw( bx, by, midx, midy );
+;        plot( midx, midy );
+;    }
+;}
+
+	clc
+	lda	X1,X
+	adc	X2,X
+	lsr
+	sta	MIDX,X
+	tay
+
+	clc
+	lda	Y1,X
+	adc	Y2,X
+	lsr
+	sta	MIDY,X
+	; plot midx,midy
+	jsr	PLOT	;; PLOT AT Y,A (A colors output, Y preserved)
+
+	; check if done
+
+	lda	X1,X
+	cmp	MIDX,X
+	bne	recurse
+
+	lda	Y1,X
+	cmp	MIDY,X
+	beq	done_draw_line
+
+recurse:
+	; draw( ax, ay, midx, midy);
+	lda	MIDX,X
+	sta	X1+1,X
+	lda	MIDY,X
+	sta	Y1+1,X
+	lda	X1,X
+	sta	X2+1,X
+	lda	Y1,X
+	sta	Y2+1,X
+
+	inx
+
+	jsr	draw_recurse
+
+	; draw( bx, by, midx, midy );
+
+	lda	X2,X
+	sta	X1+1,X
+	lda	Y2,X
+	sta	Y1+1,X
+	lda	MIDX,X
+	sta	X2+1,X
+	lda	MIDY,X
+	sta	Y2+1,X
+
+	inx
+
+	jsr	draw_recurse
+
+done_draw_line:
+	dex
+	rts
+
+