No more bg_shift

028.game2/constants.i

@@ -3,6 +3,9 @@ FOREGROUND_DELAY_BIT	equ	0
 
 FOREGROUND_SCROLL_SHIFT_CONVERT	equ	1
 FOREGROUND_SCROLL_PIXELS	equ	2
+
+BACKGROUND_SCROLL_SHIFT_CONVERT	equ	1
+BACKGROUND_SCROLL_PIXELS	equ	2
 	
 SCREEN_WIDTH		    equ 320
 SCREEN_HEIGHT		    equ 256

028.game2/game1.s

@@ -43,8 +43,7 @@ Entry:
 Reset:
 	move.l	#-FOREGROUND_SCROLL_PIXELS,foregroundScrollX		; x pos 	(d1)
 	move.l	#0,fg_tileIndex		; tile index	(d3)
-	move.l	#0,backgroundScrollX
-	move.l	#0,bg_shift		; shift counter (d2)
+	move.l	#-BACKGROUND_SCROLL_PIXELS,backgroundScrollX
 	move.l	#0,bg_tileIndex		; tile index	(d3)	
 	jsr 	BlueFill
 	move.l	#-1,frameCount		
@@ -77,9 +76,8 @@ Update:
 	bne	.skipBackgroundUpdates
 	;; ---- Background updates ----------------------------------------
 .backgroundUpdates:
-	add.l	#1,backgroundScrollX		
+	add.l	#FOREGROUND_SCROLL_PIXELS,backgroundScrollX		
 	add.l	#2,bg_tileIndex    	  ; increment tile index by a word
-	bsr 	UpdateBackgroundShiftCounter	
 .skipBackgroundUpdates:
 
 	btst	#FOREGROUND_DELAY_BIT,d6
@@ -107,7 +105,7 @@ HoriScrollPlayfield:
 	;; 	movem.l	d0-d6,-(sp)
 	
 	move.l	backgroundScrollX,d0
-	
+	lsr.l	#BACKGROUND_SCROLL_SHIFT_CONVERT,d0		; convert to pixels	
 	move.w	d0,d2
 	lsr.w   #3,d0		; bytes to scroll
 	and.w   #$F,d2		; pixels = 0xf - (hpos - (hpos_bytes*8))
@@ -188,27 +186,20 @@ ClearForegroundTile
 RenderBackgroundTile:	
 	;; a2 - map
 	move.l	backgroundScrollX,d0
+	lsr.w	#BACKGROUND_SCROLL_SHIFT_CONVERT,d0 ; convert to pixels
 	lsr.w   #3,d0		; bytes to scroll
 	move.l	backgroundOffscreen,a0
 	add.l	d0,a0
 	lea 	backgroundTilemap,a1	
 	add.l	#BITPLANE_WIDTH_BYTES-2,a0 ; dest
 	add.w	(a2),a1 	; source tile
-	move.l	bg_shift,d2
+	move.l	backgroundScrollX,d2
+	lsr.b	#BACKGROUND_SCROLL_SHIFT_CONVERT,d2		; convert to pixels
+	andi.w	#$f,d2		; find the shift component		
 	jsr	BlitTile
 	rts	
 
 
-UpdateBackgroundShiftCounter:	
-	cmp.l	#15,bg_shift	
-	bne	.s1
-	move.l	#0,bg_shift
-	bra	.s2
-.s1:
-	add.l	#1,bg_shift
-.s2:
-	rts	
-
 
 Level3InterruptHandler:
 	movem.l	d0-a6,-(sp)
@@ -280,8 +271,6 @@ foregroundScrollX:
 	dc.l	0
 fg_tileIndex:
 	dc.l	0
-bg_shift:
-	dc.l	0
 backgroundScrollX:
 	dc.l	0
 bg_tileIndex:

028.game2/image.s

@@ -17,6 +17,7 @@ SwitchBuffers:
 
 	;; background is not double buffered
 	move.l	backgroundScrollX,d0
+	lsr.l	#BACKGROUND_SCROLL_SHIFT_CONVERT,d0		; convert to pixels	
 	lsr.l   #3,d0		; bytes to scroll		
 	move.l	backgroundOnscreen,a1
 	lea 	copperListBpl2Ptr,a0