MainScreen SUBROUTINE

	JSR SixDigitDisplay
	
;Ship Movement	

;--SwitchDraw
;    TopLine == top line of sprite
;    BottomLine == bottom line of sprite ORed with $80
;   requires scanline counter < $80 (i.e., 128 lines, though you
;   can get around this by interlacing your graphics)
	
	LDY Mineral_Truck
	
        ; Calculate SwitchDraw Variables
        SEC
        LDA Ship_YPos
        STA PSWITCH
        SBC #C_SHIP_HEIGHT
        STA PEND
	
	; Subtract Height For SwitchDraw Routine
	LDA #<Sprite_Data0
	SBC PEND
	STA Ship_Ptr

	LDA Truck_Tab,Y	

	SBC PEND
	STA Ship_Ptr+2
	
	;Continue to Calculate SwitchDraw Variables
	LDA PEND
	ORA #%10000000
        STA PEND

	LDX #0
	LDA Ship_XPos
	JSR bzoneRepos 
	
	STX PF0		;prevents artifact after (Restore black border..)
	
	sleep 10

	SEC
	LDA Ship_ColorPtr
	SBC Ship_YPos	
	CLC
	ADC #C_SHIP_HEIGHT-#1
	STA Ship_ColorPtr

	STA WSYNC 
	STA HMCLR	
	
	LDX #1
	SEC
	LDA Ship_XPos
	CMP #12
	BCS NoAdjust
	ADC #161	
NoAdjust		
	SBC #8
	JSR bzoneRepos  

	STA WSYNC 
	STA HMCLR

	JSR DrawStars
	
	LDA #QUAD_SIZE_MISSILE
	STA NUSIZ0
	
	LDA #SILVER		;Ball(meteor)is color of playfield	
 	STA COLUPF	
  	TSX                   	; Transfer stack pointer to X
  	STX SavedStackPointer  	; Store it in RAM
  	LDX #ENABL		
  	TXS  	
;---------------------------------------------------------------------------------------------------
;Top Kernal	
;Begin Ship draw loop 
	;LDY #C_KERNAL_HEIGHT +#C_SHIP_HEIGHT - #1;
	
	LDY #127	;was 151 (Switchdraw maximum height is 127)
	STA WSYNC	;0	
;---------------------------------------------------------------------------------------------------
	
ShipLoop		
        ; Draw Sprite (SwitchDraw)
        CPY PSWITCH       	; 3 = 3 
        BPL PSwitch             ; 2/3 = 5
	LDA (Ship_Ptr),Y	; 5 = 10
	STA GRP0		; 3 = 13
	LDA (Ship_Ptr+2),Y	; 5 = 18	
	STA GRP1		; 3 = 21 writes must be finished before cycle 22 to avoid tearing	
PContinue
;Color for Ship loaded below
	STY 	COLUP1	; 3 = 24 
;Color for Ship loaded below
	STX 	COLUP0	; 3 = 27 		
	
;Draw Truck = 27	

;---------------------------------------------------------------------------------------------------

;DrawMissile		
	TYA                 		; 2 = 2  assuming y contains the scanline
	SBC Missile_YPos         	; 3 = 5 carry must be 1 (else use DCP)
	ADC #C_MISSILE_LENGTH   	; 2 = 7
	LDA #2		    	 	; 2 = 9
	ADC #$FF            		; 2 = 11 carry is always set!
  	STA ENAM0       		; 3 = 14 bit 1 depends on the carry after ADC
;EndMissileLoop

;Draw Stars
;Y Has Scanline 127

	LDA     StarTable,Y			;5 = 19
        STA     ENAM1			;3 = 22 waste a cycle

;Drawing Missiles =22      
;---------------------------------------------------------------------------------------------------
	
;DrawMeteor		

	CPY Meteor_YPos         ;3 Assumes Y is your kernal line counter
	PHP			;2
	LDX #ENABL		;2
	TXS			;2	
	     		
;EndMeteorLoop

;Drawing Meteors =9     

;---------------------------------------------------------------------------------------------------
;27+22+9=58

;Load Color for RCV

	LDA 	(Ship_ColorPtr),Y	;5 = 63
	TAX				;2 = 65


	NOP				;2 = 67
	NOP				;2 = 69
	
	DEY				;2 = 71
	CPY #48				;2 = 73
	BCS ShipLoop			;3 = 74
	
;---------------------------------------------------------------------------------------------------
	; SwitchDraw Routines
	
PSwitch				; 6
	bne PWait		; 2/3 = 8 
        LDA PEND                ; 3   = 11   
        STA PSWITCH		; 3   = 14
	SLEEP 4			; 4   = 18
	bcs PContinue		; 3   = 21
PWait				; 9
	STA HMCLR		; 3   = 12
	SLEEP 6			; 6   = 18
        BPL PContinue		; 3   = 21

EndShipLoop

	if (>ShipLoop != >EndShipLoop)
          echo "WARNING WARNING WARNING WARNING: ShipLoop Kernel crosses a page boundary!"
        endif	
 ;---------------------------------------------------------------------------------------------------
	
 	LDA THREE_MED_COPIES	;three buildings
	STA NUSIZ1  		;place here to minimize vertical missile stretch 
	
  	LDX SavedStackPointer
	TXS	

DrawStars SUBROUTINE

	
	LDA Star_XPos
	LDX #3
	JSR bzoneRepos	

	STA WSYNC
	STA HMCLR
	LDA     #$70            ;this value is important for the effect
	STA     HMM1
	STA     WSYNC
	STA     HMOVE
	SLEEP 16
	LDA     #$60
	STA     HMM1            ;this is the tricky part

	RTS