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A C64 Game - Step 42

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Endurion

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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.


step42.png


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


step42.zip

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