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|
;; The runtime of the game.
.scope Driver
;; Index of the current level.
zp_level = $77
;; Whenever "Select" is pressed, it's used to count how many cycles have to
;; pass before allowing another level switch.
zp_counter = $97
;; Value that will be set for the `zp_counter` whenever the "Select" button
;; is pressed for the first time.
SELECT_COUNTER_VALUE = $20
;; Initialize global variables and other variables which have an impact on
;; the runtime of the game.
.proc init
lda #0
sta Globals::zp_arg0
sta Globals::zp_arg1
sta Globals::zp_arg2
sta Globals::zp_arg3
sta Globals::zp_arg4
sta Globals::zp_tmp0
sta Globals::zp_tmp1
sta Globals::zp_tmp2
sta Globals::zp_tmp3
sta Globals::zp_idx
sta Globals::zp_flags
sta zp_level
sta zp_counter
rts
.endproc
;; Function to be called at each iteration of the game loop. It loads any
;; pending background columns and checks for level selection.
.proc update
;; Are we actually loading a new level?
lda #%00100000
and Globals::zp_flags
beq @new_level
;; Is the user actually allowed to hit the 'Select' button?
lda zp_counter
beq @check_select
dec zp_counter
jmp @check_column
@check_select:
;; If `select` is pressed, then go for a new level. Otherwise check
;; whether there is a pending column to be loaded.
lda #Joypad::BUTTON_SELECT
and Joypad::zp_buttons1
beq @check_column
;; Set the counter.
lda #SELECT_COUNTER_VALUE
sta zp_counter
;; 'Select' was pressed and we weren't loading another level. Hence,
;; increase the level index and load it.
inc zp_level
@new_level:
;; Check the level index.
ldx zp_level
cpx #$02
bne :+
ldx #$00
:
;; And load the computed level.
stx zp_level
jsr Background::load_level_x
beq :+
;; Level could be rendered, enable back the PPU.
lda PPU::zp_mask
sta PPU::MASK
;; Set the player back to its position.
RESET_PLAYER_POSITION
:
rts
@check_column:
;; Do nothing if the `column` flag is not set.
lda #%00010000
and Globals::zp_flags
beq @end
;; Continue loading the pending column.
jsr Background::load_column
beq @end
JAL Background::prepare_next_column
@end:
rts
.endproc
.endscope
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