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|
.segment "CODE"
;; The game is so simple that it can fit in both nametables. This scope has all
;; the functions and data that initializes and resets all of them properly.
.scope Assets
;; Initialize palettes and nametables.
.proc init
jsr init_palettes
;; Load the title screen on the first nametable.
lda #.lobyte(title_screen)
sta Globals::zp_arg0
lda #.hibyte(title_screen)
sta Globals::zp_arg1
ldx #$20
jsr load_screen_x
;; Ensure that the title looks as expected.
jsr prepare_for_title_screen
;; Load the main screen on the second nametable.
lda #.lobyte(main_screen)
sta Globals::zp_arg0
lda #.hibyte(main_screen)
sta Globals::zp_arg1
ldx #$28
jsr load_screen_x
rts
.endproc
;; Load the 1KB worth of screen data located via the 16-bit pointer on
;; Globals::zp_arg{0,1}. Set the `x` register to the high byte of the
;; nametable to be used.
.proc load_screen_x
bit PPU::STATUS
stx PPU::ADDRESS
lda #$00
sta PPU::ADDRESS
ldy #0
ldx #4
@loop:
lda (Globals::zp_arg0), y
sta PPU::DATA
iny
bne @loop
dex
beq @end
inc Globals::zp_arg1
jmp @loop
@end:
rts
.endproc
;; Performs all the needed tricks in order to get the first nametable as
;; expected.
.proc prepare_for_title_screen
bit PPU::STATUS
lda #$23
sta $2006
lda #$C8
sta $2006
ldx #$10
@upper_title_bar_loop:
lda #%10101010
sta $2007
dex
bne @upper_title_bar_loop
;; TODO: store back palettes after game over.
rts
.endproc
;; Performs all the needed tricks in order to get the second nametable as
;; expected.
.proc prepare_for_main_screen
;; TODO: second palette for background should be:
;; .byte $0F, $14, $2C, $28
;;
;; TODO: first palette for the foreground should be:
;; .byte $0F, $16, $10, $30
rts
.endproc
;; Copies all the palettes for our game into the proper PPU address.
.proc init_palettes
lda #$3F
sta PPU::ADDRESS
lda #$00
sta PPU::ADDRESS
ldx #0
@load_palettes_loop:
lda palettes, x
sta PPU::DATA
inx
cpx #$20
bne @load_palettes_loop
rts
palettes:
;; Background
;; 0: score
.byte $0F, $30, $2C, $28
;; 1: floating platforms
.byte $0F, $2C, $30, $2A
;; 2: ground
.byte $0F, $28, $2C, $16
;; 3: ship
.byte $0F, $16, $30, $00
;; TODO: fuel tank needs color $24
;; Foreground
;; 0: player & ship
.byte $0F, $30, $10, $30
;; 1: enemy 1 & bonuses
.byte $0F, $16, $2C, $2A
;; 2: enemy 2, fuel & bonuses
.byte $0F, $16, $14, $28
;; 3: SUSE easter egg
.byte $0F, $16, $00, $2B
.endproc
;; Having 2KB for screen data is quite wasteful, but since it's such a
;; simple game, I have so much space left in the cartridge that I can go
;; bananas with it. This helps out loading the screen as we can go faster
;; and it is less error prone.
title_screen:
.incbin "../assets/title.nam"
main_screen:
.incbin "../assets/main.nam"
.endscope
.segment "CHARS"
.incbin "../assets/jetpac.chr"
|
