; yet another moving dot by Kirk Israel
  
  processor 6502
  include vcs.h
  org $F000



YPosFromBot = $80;
VisiblePlayerLine = $81;
PlayerBuffer = $82;
PlayerVertSpeed = $83;
ButtonOnLast = $84
Temp = $85

GravTimer = $86;



;CONSTANTS
FlapStrength = #5;
GravDelay = #5 ;How often does gravity pull 'em down?
MaximumSpeed = #6 

;generic start up stuff...
Start
	SEI	
	CLD	
	TXS	
	LDX #$FF	
	LDA #0			
ClearMem 
	 STA 0,X		
	 DEX			
	 BNE ClearMem		
	 LDA #$00			
	 STA COLUBK			
	 LDA #33
	 STA COLUP0




;Some other initialization
      LDA #80
      STA YPosFromBot	;Initial Y Position
      LDA #0
      STA PlayerVertSpeed
      LDA GravDelay
      STA GravTimer


;VSYNC time
MainLoop
	LDA  #2
	STA  VSYNC	
	STA  WSYNC	
	STA  WSYNC	
	STA  WSYNC	
	LDA  #43	
	STA  TIM64T	
	LDA #0			
	STA  VSYNC		



CheckButton
	LDA INPT4
	BMI NoButton

	;Check to see if the button was already down
	LDA ButtonOnLast
	BNE ButtonWasAlreadyDown

	;New Button Pressed Time to Flap!
	LDA PlayerVertSpeed
	SEC
	SBC FlapStrength
	STA PlayerVertSpeed
	
	LDA #1
	STA ButtonOnLast
ButtonWasAlreadyDown
	JMP EndButton
NoButton    ;button wasn't pressed, remember that
	    LDA #0
	    STA ButtonOnLast
EndButton



;Time to Add Gravity to Speed?

      DEC GravTimer
      BNE DoneWithGravity

      INC PlayerVertSpeed
      LDA GravDelay
      STA GravTimer
DoneWithGravity

;See if we're going too darn fast
     LDA PlayerVertSpeed
     SEC
     SBC MaximumSpeed ; Maximum Speed

     BMI SpeedNotMaxxed ;if speed - maxspeed is positive, we need to slow down
     LDA MaximumSpeed
     STA PlayerVertSpeed

SpeedNotMaxxed







;Subtract the Player's Speed from the Position
;Add the negative of the Player Vert Speed to 0 in A
     LDA #0
     SEC
     SBC PlayerVertSpeed
;Then add the current position
      CLC
      ADC YPosFromBot
      STA YPosFromBot


FinishPositioning






;check if player hit floor
       LDA #10
       CLC
       CMP YPosFromBot
       BCC DoneCheckingHitFloor
;we need a better bounce routine, like reducing the speed?
    LDA #-4; 
    STA PlayerVertSpeed
    LDA #10
    STA YPosFromBot



DoneCheckingHitFloor



;check if player hit ceiling
       LDA #180
       CMP YPosFromBot
       BCS DoneCheckingHitCeiling

;we need a better bounce routine, like reducing the speed?
    LDA #2; 
    STA PlayerVertSpeed

    LDA #180
    STA YPosFromBot





DoneCheckingHitCeiling




;assum horiz movement will be zero
       LDX #$00	      
       LDA #$40	      ;Left?
       BIT SWCHA 
       BNE SkipMoveLeft
       LDX #$10	
       LDA %00001000
       STA REFP0
SkipMoveLeft

	LDA #$80	;Right?
	BIT SWCHA 
	BNE SkipMoveRight
	LDX #$F0	
	LDA %00000000
	STA REFP0
SkipMoveRight

	STX HMP0	;set horiz movement for player 0

WaitForVblankEnd
	LDA INTIM	
	BNE WaitForVblankEnd	
	LDY #191		

	STA VBLANK		

	STA WSYNC		
	STA HMOVE		

;main scanline loop...
ScanLoop 
	 STA WSYNC	

; here the idea is that VisiblePlayerLine
; is zero if the line isn't being drawn now,
; otherwise it's however many lines we have to go
  LDA PlayerBuffer
  STA GRP0

CheckActivatePlayer
	CPY YPosFromBot
	BNE SkipActivatePlayer
	LDA #8
	STA VisiblePlayerLine 

SkipActivatePlayer

;turn player off then see if it should be on
      LDA #00	      

;
;if the VisiblePlayerLine is non zero,
;we're drawing it
;
	LDX VisiblePlayerLine 
	BEQ FinishPlayer
IsPlayerOn  
	    LDA BigHeadGraphic-1,X
	    DEC VisiblePlayerLine 
FinishPlayer
	STA PlayerBuffer

	DEY	
	BNE ScanLoop	

	LDA #2			
	STA WSYNC		
	STA VBLANK		
	LDX #30				
OverScanWait
	STA WSYNC
	DEX
	BNE OverScanWait
	JMP MainLoop      
 
 org $FF00
BigHeadGraphic
	.byte %00111100
	.byte %01111110
	.byte %11000001
	.byte %10111111
	.byte %11111111
	.byte %11101011
	.byte %01111110
	.byte %00111100

	org $FFFC
	.word Start
	.word Start







;	LDA YPosFromBot
;	STA COLUBK