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Diffstat (limited to 'tests/src/flicker')
| -rw-r--r-- | tests/src/flicker/flicker.s | 280 |
1 files changed, 0 insertions, 280 deletions
diff --git a/tests/src/flicker/flicker.s b/tests/src/flicker/flicker.s deleted file mode 100644 index 82dcfb7..0000000 --- a/tests/src/flicker/flicker.s +++ /dev/null @@ -1,280 +0,0 @@ -;;; -;; This is a simple example of sprite cycling, so sprites don't disappear on a -;; scanline overflow. This example is extremely simple, and on a real game you'd -;; take into account lots of things that would make this process less tedious -;; and less cycle consuming. -;; Taken from https://github.com/mssola/code.nes. - -.segment "HEADER" - .byte 'N', 'E', 'S', $1A - - .byte $02, $01 - - .byte $00 - .byte $00 - -.segment "VECTORS" - .addr nmi, reset, irq - -.segment "CHARS" -.incbin "../../assets/diskun.chr" - -.segment "CODE" - -.include "../shared/diskun.s" - -.proc main - jsr Diskun::init_palettes - jsr init_sprites - - cli - lda #%10010000 - sta $2000 ; PPUCTRL - lda #%00011110 - sta $2001 ; PPUMASK - -@main_game_loop: - ;; NOTE: the logic is pretty simple: read the pad, move the player - ;; accordingly, and apply the flickering effect. - jsr joypad_read - jsr Diskun::update - - ;; NOTE: comment this `jsr` out if you want to see what happens if no - ;; flickering effect is applied (spoiler alert: the last character will - ;; suddenly disappear :P). - ;; - ;; NOTE: this function is called mindlessly. In a real game you'd try to - ;; detect scanline overflows, or you will try to be more careful with sprite - ;; priorities and apply the flickering more carefully. Here it's applied for - ;; (almost) every sprite on each frame and we roll with it. - jsr apply_flicker - - lda #%10000000 - ora $20 - sta $20 -@wait_for_render: - bit $20 - bmi @wait_for_render - - jmp @main_game_loop -.endproc - - -;;; -;; NOTE: this is the actual meat of the example :D -.proc apply_flicker - ;; We will store a 16-bit pointer to the first sprite that can be flickered. - ;; In this case, we will point to the first sprite from the first NPC. That - ;; is, we suppose that, for whatever reason, we don't want to apply the - ;; flickering effect for the player. - lda #$10 - sta $40 - lda #$02 - sta $41 - - ;;; - ;; The algorithm is really straight-forward here: we will simply cycle the - ;; sprites starting from the one being pointed at $40-$41 until the last - ;; sprite. The main idea is that the OAM will show sprites on a scanline in - ;; order. Hence, those sprites that are left beyond the eigth on a scanline - ;; will suddenly disappear. Flickering is a technique by which sprites are - ;; rotated from OAM priority, and hence they won't disappear always, but - ;; just for a small amount of time: just enough to see them, creating a - ;; flickering effect. - ;; - ;; For this, we will reserve four bytes (1 sprite) for auxiliary temporary - ;; values ($42-$45) which will then be used in order to carry values along - ;; the cycle. - - ;; We initialize the auxiliary bytes with the data from the last sprite to - ;; be iterated since these are the values to be stored for the first sprite - ;; now (that is, the last element is now the first one). - lda $24C - sta $42 - lda $24D - sta $43 - lda $24E - sta $44 - lda $24F - sta $45 - -@loop: - ;; For each of the four bytes from a sprite, pick the value stored on its - ;; auxiliary byte and save the old value into the auxiliary byte afterwards. - ;; This way the current byte holds the value from the previous sprite, but - ;; its value will be carry on into the next sprite. - .repeat 4, I - ldy #I - lda $42, y - pha - lda ($40), y - sta $42, y - pla - sta ($40), y - .endrepeat - - ;; And move the sprite pointer 4 bytes (1 sprite). Note that we only need to - ;; move the low byte since we know beforehand that everything will be inside - ;; of the $2xx range. - lda $40 - clc - adc #4 - sta $40 - - ;; We know that the last byte from the last sprite is held at $24F. Thus, if - ;; the sprite pointer is already passed this point, we can break the loop. - ;; Otherwise just carry on. - cmp #$50 - bne @loop - - rts -.endproc - -;;; -;; NOTE: and from here on stuff that is not relevant for sprite flickering. - -nmi: - bit $20 - bpl @next - - pha - txa - pha - tya - pha - - jsr Diskun::nmi_update - - lda #$00 - sta $2003 ; OAMADDR - lda #$02 - sta $4014 ; OAMDMA - - bit $2002 ; PPUSTATUS - lda #$00 - sta $2005 ; PPUSCROLL - sta $2005 ; PPUSCROLL - - lda #%01111111 - and $20 - sta $20 - - pla - tay - pla - tax - pla -@next: - rti - -reset: - sei - cld - - ldx #$40 - stx $4017 ; APU Frame Counter - - ldx #$ff - txs - - inx - stx $2000 ; PPUCTRL - stx $2001 ; PPUMASK - stx $4010 ; APU DMC - -@vblankwait1: - bit $2002 ; PPUSTATUS - bpl @vblankwait1 - - ldx #0 - lda #0 -@ram_reset_loop: - sta $000, x - sta $100, x - sta $300, x - sta $400, x - sta $500, x - sta $600, x - sta $700, x - inx - bne @ram_reset_loop ; if x overflows back to #00, then we are done. - - lda #$ef -@sprite_reset_loop: - sta $200, x - inx - bne @sprite_reset_loop - - lda #$00 - sta $2003 ; OAMADDR - lda #$02 - sta $4014 ; OAMDMA - -@vblankwait2: - bit $2002 ; PPUSTATUS - bpl @vblankwait2 - - lda #$3F - sta $2006 ; PPUADDR - lda #$00 - sta $2006 ; PPUADDR - - lda #$0F - ldx #$20 -@palettes_reset_loop: - sta $2007 ; PPUDATA - dex - bne @palettes_reset_loop - - jmp main - -irq: - rti - -.proc init_sprites - NUM_SPRITES = 20 - - lda #$40 - sta Diskun::m_screen_y - lda #$46 - sta Diskun::m_screen_x - - ldx #$00 -@load_sprites_loop: - lda initial_sprite_data, x - sta $0200, x - inx - cpx #(4 * NUM_SPRITES) - bne @load_sprites_loop - rts -initial_sprite_data: - ;; $200-$20F - .byte $40, $01, %00000000, $46 - .byte $40, $01, %01000000, $4E - .byte $48, $11, %00000000, $46 - .byte $48, $11, %01000000, $4E - - ;; $210-$21F - .byte $60, $01, %00000000, $68 - .byte $60, $01, %01000000, $70 - .byte $68, $11, %00000000, $68 - .byte $68, $11, %01000000, $70 - - ;; $220-$22F - .byte $60, $01, %00000000, $7A - .byte $60, $01, %01000000, $82 - .byte $68, $11, %00000000, $7A - .byte $68, $11, %01000000, $82 - - ;; $230-$23F - .byte $60, $01, %00000000, $8C - .byte $60, $01, %01000000, $94 - .byte $68, $11, %00000000, $8C - .byte $68, $11, %01000000, $94 - - ;; $240-$24F - .byte $60, $01, %00000000, $9E - .byte $60, $01, %01000000, $A6 - .byte $68, $11, %00000000, $9E - .byte $68, $11, %01000000, $A6 -.endproc |