A C64 Game - Step 97
And here's a little gameplay update, the bats. The diagonal movement was too predictable, so now there's more randomness to it.
The bat will move in curves. On every end of a curve the new direction will be decided randomly. Two tables are enough, however due to the C64 using two bit complement negative values are annoying to handle. Therefor I went the naive route and simply added code for every case. Ugly, but it works :)
;------------------------------------------------------------
;simply move diagonal
;------------------------------------------------------------
!zone BehaviourBatDiagonal
BehaviourBatDiagonal
jsr HandleHitBack
beq .NoHitBack
rts
.RandomDir
jsr GenerateRandomNumber
and #$07
sta SPRITE_DIRECTION,x
inc SPRITE_DIRECTION,x
lda #0
sta SPRITE_MOVE_POS,x
rts
.NoHitBack
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 BAT_ANIMATION,y
sta SPRITE_POINTER_BASE,x
.NoAnimUpdate
lda SPRITE_DIRECTION,x
beq .RandomDir
cmp #1
beq .MoveCCWWN
cmp #2
beq .MoveCCWSW
cmp #3
beq .MoveCCWES
cmp #4
beq .MoveCCWNE
cmp #5
bne +
jmp .MoveCWWS
+
cmp #6
bne +
jmp .MoveCWNW
+
cmp #7
bne +
jmp .MoveCWEN
+
cmp #8
bne +
jmp .MoveCWSE
+
.NextStep
inc SPRITE_MOVE_POS,x
lda SPRITE_MOVE_POS,x
cmp #16
bne +
lda #0
sta SPRITE_DIRECTION,x
sta SPRITE_MOVE_POS,x
+
rts
.MoveCCWWN
ldy SPRITE_MOVE_POS,x
lda PATH_CURVE,y
sta PARAM3
jsr .TryMoveUp
ldy SPRITE_MOVE_POS,x
lda PATH_CURVE_R,y
sta PARAM3
jsr .TryMoveRight
jmp .NextStep
.MoveCCWSW
ldy SPRITE_MOVE_POS,x
lda PATH_CURVE,y
sta PARAM3
jsr .TryMoveLeft
ldy SPRITE_MOVE_POS,x
lda PATH_CURVE_R,y
sta PARAM3
jsr .TryMoveUp
jmp .NextStep
.MoveCCWES
ldy SPRITE_MOVE_POS,x
lda PATH_CURVE,y
sta PARAM3
jsr .TryMoveDown
ldy SPRITE_MOVE_POS,x
lda PATH_CURVE_R,y
sta PARAM3
jsr .TryMoveLeft
jmp .NextStep
.MoveCCWNE
ldy SPRITE_MOVE_POS,x
lda PATH_CURVE,y
sta PARAM3
jsr .TryMoveRight
ldy SPRITE_MOVE_POS,x
lda PATH_CURVE_R,y
sta PARAM3
jsr .TryMoveDown
jmp .NextStep
.MoveCWWS
ldy SPRITE_MOVE_POS,x
lda PATH_CURVE,y
sta PARAM3
jsr .TryMoveDown
ldy SPRITE_MOVE_POS,x
lda PATH_CURVE_R,y
sta PARAM3
jsr .TryMoveRight
jmp .NextStep
.MoveCWNW
ldy SPRITE_MOVE_POS,x
lda PATH_CURVE,y
sta PARAM3
jsr .TryMoveLeft
ldy SPRITE_MOVE_POS,x
lda PATH_CURVE_R,y
sta PARAM3
jsr .TryMoveDown
jmp .NextStep
.MoveCWEN
ldy SPRITE_MOVE_POS,x
lda PATH_CURVE,y
sta PARAM3
jsr .TryMoveUp
ldy SPRITE_MOVE_POS,x
lda PATH_CURVE_R,y
sta PARAM3
jsr .TryMoveLeft
jmp .NextStep
.MoveCWSE
ldy SPRITE_MOVE_POS,x
lda PATH_CURVE,y
sta PARAM3
jsr .TryMoveRight
ldy SPRITE_MOVE_POS,x
lda PATH_CURVE_R,y
sta PARAM3
jsr .TryMoveUp
jmp .NextStep
.Blocked
lda #0
sta SPRITE_DIRECTION,x
rts
.TryMoveUp
beq +
jsr ObjectMoveUpBlocking
beq .Blocked
dec PARAM3
jmp .TryMoveUp
+
rts
.TryMoveDown
beq +
jsr ObjectMoveDownBlocking
beq .Blocked
dec PARAM3
jmp .TryMoveDown
+
rts
.TryMoveLeft
beq +
jsr ObjectMoveLeftBlocking
beq .Blocked
dec PARAM3
jmp .TryMoveLeft
+
rts
.TryMoveRight
beq +
jsr ObjectMoveRightBlocking
beq .Blocked
dec PARAM3
jmp .TryMoveRight
+
rts
The table are simple delta updates per frame, one being the reverse of the other:
PATH_CURVE
!byte 0
!byte 0
!byte 1
!byte 0
!byte 0
!byte 1
!byte 0
!byte 1
!byte 0
!byte 1
!byte 1
!byte 1
!byte 1
!byte 1
!byte 1
!byte 1
PATH_CURVE_R
!byte 1
!byte 1
!byte 1
!byte 1
!byte 1
!byte 1
!byte 1
!byte 0
!byte 1
!byte 0
!byte 1
!byte 0
!byte 0
!byte 1
!byte 0
!byte 0
The other thing is a little fix for a bug I found with the vanishing bats for the last portal stages. The bats could appear outside the playing area. The fix are two border values for left and right which will be set to be farther inside the screen if a portal level is run:
;set default
lda #10
sta SPAWN_LEFT_BORDER
lda #30
sta SPAWN_RIGHT_BORDER
;adjust spawn border on portal level
lda LEVEL_CONFIG
and #$04
beq +
lda #15
sta SPAWN_LEFT_BORDER
lda #25
sta SPAWN_RIGHT_BORDER
+
...and adjust the spawn code inside BehaviourBatVanishing:
;position diagonal above/below player
lda SPRITE_CHAR_POS_X
cmp #SPAWN_LEFT_BORDER
;was #10
bcc .SpawnOnRight
cmp #SPAWN_RIGHT_BORDER
;was #30
bcs .SpawnOnLeft
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