Create a custom theme
Nothing really new this time, just constant use of existing parts. A new enemy, some sort of mummy, which slowly walks back and forth. And takes a few more hits than the bats.
It's a new behaviour added to the table and some extra code that checks for gaps before walking.
Adding the enemy itself is nothing more than adding new entries to the existing tables
The behaviour code looks quite simple, as most of the new code is inside subroutines ObjectWalkLeft/ObjectWalkRight.
The new subroutines are a more complex version of ObjectMoveLeft/ObjectMoveRight. They add a new check, so the enemy only walks forward, if it's not blocked and there is no gap in the floor in front:
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It's a new behaviour added to the table and some extra code that checks for gaps before walking.
Adding the enemy itself is nothing more than adding new entries to the existing tables
;object type constants TYPE_PLAYER = 1 TYPE_BAT_LR = 2 TYPE_BAT_UD = 3 TYPE_BAT_8 = 4 TYPE_MUMMY = 5 ENEMY_BEHAVIOUR_TABLE_LO !byte <PlayerControl !byte <BehaviourBatLR !byte <BehaviourBatUD !byte <BehaviourBat8 !byte <BehaviourMummy ENEMY_BEHAVIOUR_TABLE_HI !byte >PlayerControl !byte >BehaviourBatLR !byte >BehaviourBatUD !byte >BehaviourBat8 !byte >BehaviourMummy IS_TYPE_ENEMY !byte 0 ;dummy entry for inactive object !byte 0 ;player !byte 1 ;bat_lr !byte 1 ;bat_ud !byte 1 ;bat 8 !byte 1 ;mummy TYPE_START_SPRITE !byte 0 ;dummy entry for inactive object !byte SPRITE_PLAYER_STAND_R !byte SPRITE_BAT_1 !byte SPRITE_BAT_1 !byte SPRITE_BAT_2 !byte SPRITE_MUMMY_R_1 TYPE_START_COLOR !byte 0 !byte 10 !byte 3 !byte 3 !byte 8 !byte 1 TYPE_START_MULTICOLOR !byte 0 !byte 1 !byte 0 !byte 0 !byte 0 !byte 0 TYPE_START_HP !byte 0 !byte 1 !byte 5 !byte 5 !byte 5 !byte 10
The behaviour code looks quite simple, as most of the new code is inside subroutines ObjectWalkLeft/ObjectWalkRight.
;------------------------------------------------------------ ;simply walk left/right, do not fall off ;------------------------------------------------------------ !zone BehaviourMummy BehaviourMummy lda DELAYED_GENERIC_COUNTER and #$3 beq .MovementUpdate rts .MovementUpdate inc SPRITE_MOVE_POS,x lda SPRITE_MOVE_POS,x and #$7 sta SPRITE_MOVE_POS,x cmp #4 bpl .CanMove rts .CanMove lda SPRITE_DIRECTION,x beq .MoveRight ;move left jsr ObjectWalkLeft beq .ToggleDirection rts .MoveRight jsr ObjectWalkRight beq .ToggleDirection rts .ToggleDirection lda SPRITE_DIRECTION,x eor #1 sta SPRITE_DIRECTION,x rts
The new subroutines are a more complex version of ObjectMoveLeft/ObjectMoveRight. They add a new check, so the enemy only walks forward, if it's not blocked and there is no gap in the floor in front:
;------------------------------------------------------------ ;walk object right if not blocked, do not fall off ;x = object index ;------------------------------------------------------------ !zone ObjectWalkRight ObjectWalkRight lda SPRITE_CHAR_POS_X_DELTA,x beq .CheckCanMoveRight .CanMoveRight inc SPRITE_CHAR_POS_X_DELTA,x lda SPRITE_CHAR_POS_X_DELTA,x cmp #8 bne .NoCharStep lda #0 sta SPRITE_CHAR_POS_X_DELTA,x inc SPRITE_CHAR_POS_X,x .NoCharStep jsr MoveSpriteRight lda #1 rts .CheckCanMoveRight 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 IsCharBlockingFall beq .BlockedRight ldy SPRITE_CHAR_POS_Y,x dey 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 .BlockedRight tya clc adc #40 tay lda (ZEROPAGE_POINTER_1),y jsr IsCharBlocking bne .BlockedRight jmp .CanMoveRight .BlockedRight lda #0 rts
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Attached Files
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step19.zip (18.16K)
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