diff --git a/build.sh b/build.sh
index eba54f1..005ccd6 100755
--- a/build.sh
+++ b/build.sh
@@ -24,5 +24,5 @@ rm -f ./bin/emulator
 cc -std=c89 -DDEBUG -Wall -Wno-unknown-pragmas -Wpedantic -Wshadow -Wextra -Werror=implicit-int -Werror=incompatible-pointer-types -Werror=int-conversion -Wvla -g -Og -fsanitize=address -fsanitize=undefined uxn.c emulator.c -L/usr/local/lib -lSDL2 -o bin/emulator
 
 # run
-./bin/assembler examples/line.usm bin/boot.rom
+./bin/assembler examples/draw.usm bin/boot.rom
 ./bin/emulator bin/boot.rom
diff --git a/examples/draw.usm b/examples/draw.usm
index 5b1387a..c25a986 100644
--- a/examples/draw.usm
+++ b/examples/draw.usm
@@ -4,6 +4,7 @@
 :dev/w fff9 ( std write port )
 
 ;x_ 2 ;y_ 2 ;x 2 ;y 2 ;w 2 ;h 2 ;color 1
+;x0 2 ;y0 2 ;x1 2 ;y1 2 ;dx 2 ;dy 2 ;err1 2 ;err2 2 ( line )
 
 |0100 @RESET
 
@@ -38,6 +39,23 @@
 	( fill rect x y w h )
 	,0028 ,0038 ,0050 ,0030 ,linerect JSR
 
+
+	( positive )
+	,01 ,color STR
+	+0030 ,x0 STR^ +0040 ,y0 STR^
+	+0100 ,x1 STR^ +0060 ,y1 STR^
+	,line JSR
+
+	,02 ,color STR
+	+0020 ,x0 STR^ +0010 ,y0 STR^
+	+0090 ,x1 STR^ +0070 ,y1 STR^
+	,line JSR
+
+	,03 ,color STR
+	+0010 ,x0 STR^ +0040 ,y0 STR^
+	+0070 ,x1 STR^ +0060 ,y1 STR^
+	,line JSR
+
 	,redraw JSR
 
 BRK
@@ -70,6 +88,31 @@ BRK
 		,x_ LDR^ ,w LDR^ ,x LDR^ ADD^ ,0001 ADD^ LTH^ ,linerectrow ROT JMP? POP^
 	RTS
 
+@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!^ ,err1 STR^                    ( int err1 = dx + dy, e2; )
+	@lineloop
+	,x_ LDR^ ,y_ LDR^ ,putpixel JSR                       ( draw )
+	@line-x
+	,err1 LDR^ +0002 MUL!^ ,err2 STR^                     ( e2 = 2 * err; )
+	,err2 LDR^ ,dy LDR^ LTH!^ ,line-y ROT JMP? POP^ 	  ( e2 >= dy )
+		,err1 LDR^ ,dy LDR^ ADD!^ ,err1 STR^ 			  ( err1 += dy; )
+		,x_ LDR^ +0001 ADD!^ ,x_ STR^                     ( y0 += y0 < y1 ? 1 : -1; )
+	@line-y
+	,err2 LDR^ ,dx LDR^ GTH!^ ,line-end ROT JMP? POP^     ( e2 <= dx )
+		,err1 LDR^ ,dx LDR^ ADD!^ ,err1 STR^              ( err1 += dx; )
+		,y_ LDR^ +0001 ADD!^ ,y_ STR^                     ( y0 += y0 < y1 ? 1 : -1; )
+	@line-end
+	,x_ LDR^ ,x1 LDR^ NEQ!^ ,lineloop ROT JMP? POP^       ( loop )
+	RTS
+
+@diff16
+	OVR^ OVR^ GTH^ ,diff16sub ROT JMP? POP^
+	SWP^ @diff16sub SUB^
+RTS
+
 @redraw
 	,0000 IOW^
 	,0000 IOW^
diff --git a/examples/line.usm b/examples/line.usm
index 9df80a8..8af9d00 100644
--- a/examples/line.usm
+++ b/examples/line.usm
@@ -3,27 +3,28 @@
 :dev/r fff8 ( std read port )
 :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
+;x_ 2 ;y_ 2 ;color 1
+;x0 2 ;y0 2 ;x1 2 ;y1 2 ;dx 2 ;dy 2 ;err1 2 ;err2 2
 
 |0100 @RESET
 
 	( set dev/write to screen ) 
 	,01 ,dev/w STR 
 
+	( positive )
 	,01 ,color STR
 	+0030 ,x0 STR^ +0040 ,y0 STR^
-	+0050 ,x1 STR^ +0060 ,y1 STR^
+	+0100 ,x1 STR^ +0060 ,y1 STR^
 	,line JSR
 
 	,02 ,color STR
 	+0020 ,x0 STR^ +0010 ,y0 STR^
-	+0060 ,x1 STR^ +0070 ,y1 STR^
+	+0090 ,x1 STR^ +0070 ,y1 STR^
 	,line JSR
 
 	,03 ,color STR
 	+0010 ,x0 STR^ +0040 ,y0 STR^
-	+0080 ,x1 STR^ +0060 ,y1 STR^
+	+0070 ,x1 STR^ +0060 ,y1 STR^
 	,line JSR
 
 	( draw control points )
@@ -39,19 +40,20 @@ BRK
 	,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
+	,dx LDR^ ,dy LDR^ ADD!^ ,err1 STR^                    ( int err1 = dx + dy, e2; )
+	@lineloop
 	,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; )
+	@line-x
+	,err1 LDR^ +0002 MUL!^ ,err2 STR^                     ( e2 = 2 * err; )
+	,err2 LDR^ ,dy LDR^ LTH!^ ,line-y ROT JMP? POP^ 	  ( e2 >= dy )
+		,err1 LDR^ ,dy LDR^ ADD!^ ,err1 STR^ 			  ( err1 += 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; )
+	@line-y
+	,err2 LDR^ ,dx LDR^ GTH!^ ,line-end ROT JMP? POP^     ( e2 <= dx )
+		,err1 LDR^ ,dx LDR^ ADD!^ ,err1 STR^              ( err1 += dx; )
 		,y_ LDR^ +0001 ADD!^ ,y_ STR^                     ( y0 += y0 < y1 ? 1 : -1; )
-	@continue2
-	,x_ LDR^ ,x1 LDR^ LTH!^ ,loop ROT JMP? POP^           ( loop )
+	@line-end
+	,x_ LDR^ ,x1 LDR^ NEQ!^ ,lineloop ROT JMP? POP^       ( loop )
 	RTS
 
 @redraw