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A C64 Game - Step 42

Posted by Endurion, in C64 18 February 2012 · 443 views

So after a break last week we carry on. There were even more enemy sprites created, so here we go. New are the floating ghost and the fly.

The floating ghost is homing in on the player, but currently blocked by platforms downwards. To amend this we add a new routine. It's a clone of ObjectMoveDownBlocking, the only difference is the call to IsCharBlocking.

;------------------------------------------------------------
;move object down if not blocked
;x = object index
;------------------------------------------------------------
!zone ObjectMoveDownBlockingNoPlatform
ObjectMoveDownBlockingNoPlatform
		
		  lda SPRITE_CHAR_POS_Y_DELTA,x
		  beq .CheckCanMoveDown
		
.CanMoveDown
		  inc SPRITE_CHAR_POS_Y_DELTA,x
		
		  lda SPRITE_CHAR_POS_Y_DELTA,x
		  cmp #8
		  bne .NoCharStep
		
		  lda #0
		  sta SPRITE_CHAR_POS_Y_DELTA,x
		  inc SPRITE_CHAR_POS_Y,x
		
.NoCharStep		
		  jsr MoveSpriteDown
		  lda #1
		  rts
		
.CheckCanMoveDown
		  lda SPRITE_CHAR_POS_X_DELTA,x
		  beq .NoSecondCharCheckNeeded
		
		  ldy SPRITE_CHAR_POS_Y,x
		  iny
		  lda SCREEN_LINE_OFFSET_TABLE_LO,y
		  sta ZEROPAGE_POINTER_1
		  lda SCREEN_BACK_LINE_OFFSET_TABLE_HI,y
		  sta ZEROPAGE_POINTER_1 + 1
		  ldy SPRITE_CHAR_POS_X,x
		  iny
		  lda (ZEROPAGE_POINTER_1),y
		
		  jsr IsCharBlocking
		  bne .BlockedDown
		
.NoSecondCharCheckNeeded		
		  ldy SPRITE_CHAR_POS_Y,x
		  iny
		  lda SCREEN_LINE_OFFSET_TABLE_LO,y
		  sta ZEROPAGE_POINTER_1
		  lda SCREEN_BACK_LINE_OFFSET_TABLE_HI,y
		  sta ZEROPAGE_POINTER_1 + 1
		
		  ldy SPRITE_CHAR_POS_X,x
		
		  lda (ZEROPAGE_POINTER_1),y
		
		  jsr IsCharBlocking
		  bne .BlockedDown
		
		  jmp .CanMoveDown
		
.BlockedDown
		  lda #0
		  rts

We had code for the ghost skeleton last week, but it was only animating. Now here comes the homing in part. The most annoying part is actually to decide which player to follow. For now it settles on one of the two, that may be subject to change later.

;------------------------------------------------------------
;ghost skeleton
;------------------------------------------------------------
!zone BehaviourGhostSkeleton
BehaviourGhostSkeleton
GHOST_MOVE_SPEED = 1
		  lda DELAYED_GENERIC_COUNTER
		  and #$03
		  bne .NoAnimUpdate
		
		  inc SPRITE_ANIM_POS,x
		  lda SPRITE_ANIM_POS,x
		  and #$03
		  sta SPRITE_ANIM_POS,x
		
		  tay
		  lda GHOST_SKELETON_ANIMATION_TABLE,y
		  sta SPRITE_POINTER_BASE,x
		
.NoAnimUpdate		
		  inc SPRITE_ANIM_DELAY,x
		  lda SPRITE_ANIM_DELAY,x
		  cmp #10
		  beq .DoCheckMove
		  jmp .DoGhostMove
.DoCheckMove
		  lda #0
		  sta SPRITE_ANIM_DELAY,x
		
		  txa
		  and #$01
		  tay
		  lda SPRITE_ACTIVE,y
		  cmp #TYPE_PLAYER_DEAN
		  beq .FoundPlayer
		  cmp #TYPE_PLAYER_SAM
		  beq .FoundPlayer
		
		  ;check other player
		  tya
		  eor #1
		  tay
		  lda SPRITE_ACTIVE,y
		  cmp #TYPE_PLAYER_DEAN
		  beq .FoundPlayer
		  cmp #TYPE_PLAYER_SAM
		  beq .FoundPlayer
		
		  ;no player to hunt
		  rts
.FoundPlayer
		  ;player index in y
		  lda SPRITE_CHAR_POS_X,y
		  cmp SPRITE_CHAR_POS_X,x
		  bpl .MoveRight
		
		  ;move left
		  lda SPRITE_DIRECTION,x
		  bne .AlreadyLookingLeft
		  lda SPRITE_MOVE_POS,x
		  beq .TurnLNow
		  dec SPRITE_MOVE_POS,x
		  bne .CheckYNow
		
.TurnLNow		
		  ;turning now
		  lda #1
		  sta SPRITE_DIRECTION,x
		  jmp .CheckYNow
		
.AlreadyLookingLeft
		  lda SPRITE_MOVE_POS,x
		  cmp #GHOST_MOVE_SPEED
		  beq .CheckYNow
		  inc SPRITE_MOVE_POS,x
		  jmp .CheckYNow
		
.MoveRight  
		  lda SPRITE_DIRECTION,x
		  beq .AlreadyLookingRight
		
		  lda SPRITE_MOVE_POS,x
		  beq .TurnRNow
		  dec SPRITE_MOVE_POS,x
		  bne .CheckYNow
		
		  ;turning now
.TurnRNow		
		  lda #0
		  sta SPRITE_DIRECTION,x
		  jmp .CheckYNow
		
.AlreadyLookingRight		
		  lda SPRITE_MOVE_POS,x
		  cmp #GHOST_MOVE_SPEED
		  beq .CheckYNow
		  inc SPRITE_MOVE_POS,x
		  jmp .CheckYNow
		
.CheckYNow
		  ;player index in y
		  lda SPRITE_CHAR_POS_Y,y
		  cmp SPRITE_CHAR_POS_Y,x
		  bpl .MoveDown
		
		  ;move left
		  lda SPRITE_DIRECTION_Y,x
		  bne .AlreadyLookingUp
		  lda SPRITE_MOVE_POS_Y,x
		  beq .TurnUNow
		  dec SPRITE_MOVE_POS_Y,x
		  bne .DoGhostMove
		
.TurnUNow		
		  ;turning now
		  lda #1
		  sta SPRITE_DIRECTION_Y,x
		  jmp .DoGhostMove
		
.AlreadyLookingUp
		  lda SPRITE_MOVE_POS_Y,x
		  cmp #GHOST_MOVE_SPEED
		  beq .DoGhostMove
		  inc SPRITE_MOVE_POS_Y,x
		  jmp .DoGhostMove
		
.MoveDown
		  lda SPRITE_DIRECTION_Y,x
		  beq .AlreadyLookingDown
		
		  lda SPRITE_MOVE_POS_Y,x
		  beq .TurnDNow
		  dec SPRITE_MOVE_POS_Y,x
		  bne .DoGhostMove
		
		  ;turning now
.TurnDNow		
		  lda #0
		  sta SPRITE_DIRECTION_Y,x
		  jmp .DoGhostMove
		
.AlreadyLookingDown
		  lda SPRITE_MOVE_POS_Y,x
		  cmp #GHOST_MOVE_SPEED
		  beq .DoGhostMove
		  inc SPRITE_MOVE_POS_Y,x
		  jmp .DoGhostMove
.DoGhostMove
		  ;move X times
		  ldy SPRITE_MOVE_POS,x
		  sty PARAM4
		  beq .DoY
		
		  lda SPRITE_DIRECTION,x
		  beq .DoRight
.MoveLoopL
		  jsr ObjectMoveLeftBlocking
		  dec PARAM4
		  bne .MoveLoopL
		  jmp .DoY
		
.DoRight
.MoveLoopR
		  jsr ObjectMoveRightBlocking
		  dec PARAM4
		  bne .MoveLoopR
		
.DoY		
		  ;move X times
		  ldy SPRITE_MOVE_POS_Y,x
		  sty PARAM4
		  beq .MoveDone
		
		  lda SPRITE_DIRECTION_Y,x
		  beq .DoDown
.MoveLoopU
		  jsr ObjectMoveUpBlocking
		  dec PARAM4
		  bne .MoveLoopU
		  jmp .MoveDone
		
.DoDown
.MoveLoopD
		  jsr ObjectMoveDownBlockingNoPlatform
		  dec PARAM4
		  bne .MoveLoopD
.MoveDone		
		  rts

And last but not least, the annoying fly. Moving randomly about it surely annoys the heck out of you.

;------------------------------------------------------------
;move randomly diagonal
;------------------------------------------------------------
!zone BehaviourFly
BehaviourFly
		  lda DELAYED_GENERIC_COUNTER
		  and #$01
		  bne .NoAnimUpdate
		
		  lda SPRITE_ANIM_POS,x
		  eor #1
		  sta SPRITE_ANIM_POS,x
		
		  clc
		  adc #SPRITE_FLY_1
		  sta SPRITE_POINTER_BASE,x
		
.NoAnimUpdate		
		  lda SPRITE_STATE,x
		  beq .Move
		  dec SPRITE_MOVE_POS,x
		  bne .NoAction
		
		  ;can move again
		  dec SPRITE_STATE,x
		
		  jsr GenerateRandomNumber
		  sta SPRITE_MOVE_POS,x
		
		  jsr GenerateRandomNumber
		  and #$03
		  cmp #3
		  bne .ValueOK
		
		  lda #2
.ValueOK		
		  sta SPRITE_DIRECTION,x
		  jsr GenerateRandomNumber
		  and #$03
		  cmp #3
		  bne .ValueOK2
		
		  lda #2
.ValueOK2
		  sta SPRITE_DIRECTION_Y,x
.NoAction		
		  rts
		
.Move
		  dec SPRITE_MOVE_POS,x
		  bne .CanMove
		
		  ;wait
		  jsr GenerateRandomNumber
		  sta SPRITE_MOVE_POS,x
		
		  inc SPRITE_STATE,x
		  rts
		
.CanMove		
		  lda SPRITE_DIRECTION,x
		  beq .MoveRight
		  cmp #2
		  beq .MoveY
		
		  ;move left
		  jsr ObjectMoveLeftBlocking
		  beq .ToggleDirection
		  jmp .MoveY
		
.MoveRight
		  jsr ObjectMoveRightBlocking
		  beq .ToggleDirection
		  jmp .MoveY
		
.ToggleDirection
		  lda SPRITE_DIRECTION,x
		  eor #1
		  sta SPRITE_DIRECTION,x
		
.MoveY
		  lda SPRITE_DIRECTION_Y,x
		  beq .MoveDown
		  cmp #2
		  beq .NoYMovement
		
		  ;move up
		  jsr ObjectMoveUpBlocking
		  beq .ToggleDirectionY
		  rts
		
.MoveDown
		  jsr ObjectMoveDownBlockingNoPlatform
		  beq .ToggleDirectionY
		
.NoYMovement		
		  rts
		
.ToggleDirectionY
		  lda SPRITE_DIRECTION_Y,x
		  eor #1
		  sta SPRITE_DIRECTION_Y,x
		  rts

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