From 835123f94ad70de477832ca9846077f3b6d0b735 Mon Sep 17 00:00:00 2001
From: neauoire <aliceffekt@gmail.com>
Date: Fri, 12 Feb 2021 17:56:17 -0800
Subject: [PATCH] Drawing basic line

---
 assembler.c       |  1 -
 examples/line.usm | 33 ++++++++++++++++++++++++++++-----
 2 files changed, 28 insertions(+), 6 deletions(-)

diff --git a/assembler.c b/assembler.c
index 7bf7928..05bbd61 100644
--- a/assembler.c
+++ b/assembler.c
@@ -63,7 +63,6 @@ pushbyte(Uint8 b, int lit)
 void
 pushshort(Uint16 s, int lit)
 {
-	printf("%04x[%d]\n", s, lit);
 	if(lit) {
 		pushbyte(0x03, 0);
 		pushbyte(0x02, 0);
diff --git a/examples/line.usm b/examples/line.usm
index bc053c5..a709c34 100644
--- a/examples/line.usm
+++ b/examples/line.usm
@@ -4,20 +4,24 @@
 :dev/w fff9 ( std write port )
 
 ;x_ 2 ;y_ 2 ;x0 2 ;y0 2 ;x1 2 ;y1 2 ;color 1
-
 ;dx 2 ;dy 2 ;err 2 ;err2 2
 
 |0100 @RESET
 
 	( set dev/write to screen ) 
 	,01 ,dev/w STR 
+
 	,01 ,color STR
+	+0030 ,x0 STR^ +0040 ,y0 STR^
+	+0050 ,x1 STR^ +0060 ,y1 STR^
 
-	( init positions )
-	,0020 ,x0 STR^ ,0018 ,y0 STR^
-	,0060 ,x1 STR^ ,0048 ,y1 STR^
-	,x0 LDR^ ,x_ STR^ ,y0 LDR^ ,y_ STR^
+	,line JSR
 
+	,02 ,color STR
+	+0020 ,x0 STR^ +0010 ,y0 STR^
+	+0060 ,x1 STR^ +0070 ,y1 STR^
+
+	,line JSR
 
 	( draw control points )
 	,02 ,color STR
@@ -28,6 +32,25 @@
 
 BRK
 
+@line
+	,x0 LDR^ ,x_ STR^ ,y0 LDR^ ,y_ STR^                   ( start at x0,y0 )
+	,x1 LDR^ ,x0 LDR^ ,diff16sub JSR ,dx STR^             ( int dx = abs[x1 - x0] )
+	,y1 LDR^ ,y0 LDR^ ,diff16sub JSR -0001 MUL!^ ,dy STR^ ( int dy = -abs[y1 - y0] )
+	,dx LDR^ ,dy LDR^ ADD!^ ,err STR^                     ( int err = dx + dy, e2; )
+	@loop
+	,x_ LDR^ ,y_ LDR^ ,putpixel JSR                       ( draw )
+	,err LDR^ +0002 MUL!^ ,err2 STR^                      ( e2 = 2 * err; )
+	,err2 LDR^ ,dy LDR^ LTH!^ ,continue1 ROT JMP? POP^ 	  ( e2 >= dy )
+		,err LDR^ ,dy LDR^ ADD!^ ,err STR^ 				  ( err += dy; )
+		,x_ LDR^ +0001 ADD!^ ,x_ STR^                     ( y0 += y0 < y1 ? 1 : -1; )
+	@continue1
+	,err2 LDR^ ,dx LDR^ GTH!^ ,continue2 ROT JMP? POP^    ( e2 <= dx )
+		,err LDR^ ,dx LDR^ ADD!^ ,err STR^                ( err += dx; )
+		,y_ LDR^ +0001 ADD!^ ,y_ STR^                     ( y0 += y0 < y1 ? 1 : -1; )
+	@continue2
+	,x_ LDR^ ,x1 LDR^ LTH!^ ,loop ROT JMP? POP^           ( loop )
+	RTS
+
 @redraw
 	,0000 IOW^
 	,0000 IOW^