375 lines
7.8 KiB
NASM
375 lines
7.8 KiB
NASM
; -----------------------------------------------------------
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; transitions.asm - slide transitions
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; every slide is drawn with the display switched off, its
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; colors are snapshotted into FADEBUF and blackened, then an
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; in-transition reveals it; an out-transition hides it again.
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; types (picked per slide in tin_tbl/tout_tbl in main.asm):
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; TR_FADE - fade through black via the fadetbl ramps
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; TR_DISSOLVE - cells appear/vanish in random (LFSR) order
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; TR_WIPE - column sweep from left to right
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; each reveal starts with a short grey border flash
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; -----------------------------------------------------------
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; ---- draw the current slide while the display is switched off
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; (everything shows border color = black), snapshot its colors,
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; blacken them, switch the display back on, flash, transition in ----
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show_slide:
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lda #$0b ; display off
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sta SCRCTRL
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jsr slide_setup
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jsr snapshot_colram
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lda #$1b ; display on
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sta SCRCTRL
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ldx #0 ; short white-to-grey border flash: gives
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ssf_loop: ; the reveal a beat
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lda flashtbl,x
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sta BORDER
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jsr wait_frame
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inx
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cpx #3
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bne ssf_loop
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lda #BLACK
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sta BORDER
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ldx slide ; dispatch the slide's in-transition
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ldy tin_tbl,x
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lda tin_lo,y
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sta vec
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lda tin_hi,y
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sta vec+1
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jmp (vec) ; the transition ends with rts
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; ---- dispatch the slide's out-transition ----
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trans_out:
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lda #0 ; sprites vanish with the slide
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sta SPR_EN
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ldx slide
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ldy tout_tbl,x
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lda tout_lo,y
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sta vec
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lda tout_hi,y
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sta vec+1
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jmp (vec)
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tin_lo:
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!byte <fade_in, <dissolve_in, <wipe_in
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tin_hi:
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!byte >fade_in, >dissolve_in, >wipe_in
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tout_lo:
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!byte <fade_out, <dissolve_out, <wipe_out
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tout_hi:
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!byte >fade_out, >dissolve_out, >wipe_out
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flashtbl:
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!byte WHITE, LGREY, DGREY
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; ============================================================
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; TR_FADE - fade through black
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; ============================================================
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; ---- fade in: fadecnt counts how many times the target color is
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; darkened; counting 4 -> 0 walks each cell from black back
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; up to its snapshot color ----
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fade_in:
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lda #FADE_STEPS-1
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sta fadecnt
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fi_step:
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jsr build_map
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jsr apply_map
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ldx #FADE_SPEED
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fi_wait:
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jsr wait_frame
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dex
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bne fi_wait
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lda fadecnt
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beq fi_done
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dec fadecnt
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jmp fi_step
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fi_done:
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rts
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; ---- darken the whole color RAM step by step until black ----
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fade_out:
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lda #FADE_STEPS
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sta fadecnt
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fo_step:
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ldx #FADE_SPEED
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fo_wait:
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jsr wait_frame
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dex
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bne fo_wait
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jsr apply_fade
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dec fadecnt
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bne fo_step
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rts
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; ---- one fade-out step: every color RAM cell one shade darker ----
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apply_fade:
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ldx #0
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af_loop:
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lda COLRAM,x
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and #15 ; color RAM reads have garbage upper bits
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tay
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lda fadetbl,y
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sta COLRAM,x
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lda COLRAM+250,x
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and #15
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tay
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lda fadetbl,y
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sta COLRAM+250,x
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lda COLRAM+500,x
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and #15
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tay
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lda fadetbl,y
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sta COLRAM+500,x
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lda COLRAM+750,x
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and #15
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tay
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lda fadetbl,y
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sta COLRAM+750,x
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inx
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cpx #250
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bne af_loop
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rts
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; ---- curmap[c] = color c darkened fadecnt times ----
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build_map:
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ldx #15
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bm_color:
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txa
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tay
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lda fadecnt
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sta bmcnt
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beq bm_store ; 0 steps: identity map
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bm_apply:
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lda fadetbl,y
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tay
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dec bmcnt
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bne bm_apply
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bm_store:
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tya
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sta curmap,x
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dex
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bpl bm_color
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rts
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; ---- write curmap[FADEBUF] into the whole color RAM ----
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apply_map:
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ldx #0
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am_loop:
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ldy FADEBUF,x
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lda curmap,y
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sta COLRAM,x
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ldy FADEBUF+250,x
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lda curmap,y
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sta COLRAM+250,x
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ldy FADEBUF+500,x
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lda curmap,y
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sta COLRAM+500,x
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ldy FADEBUF+750,x
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lda curmap,y
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sta COLRAM+750,x
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inx
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cpx #250
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bne am_loop
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rts
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; ============================================================
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; TR_DISSOLVE - cells appear/vanish in random order
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; a 10-bit LFSR walks all indexes 1..1023 exactly once per
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; period; indexes >= 1000 are skipped, cell 0 (which the LFSR
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; never yields) is handled up front. 25 cells per frame ->
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; the full screen takes 40 frames (0.8 s).
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; ============================================================
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dissolve_in:
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lda FADEBUF ; cell 0 first
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sta COLRAM
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lda #40
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sta frcnt
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din_frame:
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jsr wait_frame
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lda #25
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sta cellcnt
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din_cell:
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jsr lfsr_next ; -> lfsrlo/hi = cell index 1..999
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lda lfsrlo
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sta scrlo
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sta collo
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lda lfsrhi
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clc
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adc #>FADEBUF
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sta scrhi
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lda lfsrhi
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clc
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adc #>COLRAM
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sta colhi
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ldy #0
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lda (scrlo),y ; restore the snapshot color
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sta (collo),y
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dec cellcnt
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bne din_cell
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dec frcnt
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bne din_frame
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rts
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dissolve_out:
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lda #BLACK ; cell 0 first
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sta COLRAM
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lda #40
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sta frcnt
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dot_frame:
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jsr wait_frame
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lda #25
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sta cellcnt
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dot_cell:
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jsr lfsr_next
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lda lfsrlo
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sta collo
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lda lfsrhi
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clc
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adc #>COLRAM
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sta colhi
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ldy #0
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lda #BLACK
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sta (collo),y
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dec cellcnt
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bne dot_cell
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dec frcnt
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bne dot_frame
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rts
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; ---- 10-bit Galois LFSR (x^10 + x^7 + 1, period 1023) ----
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; steps until the state is a valid cell index (< 1000); the
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; state is never reset, coverage holds from any starting point
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lfsr_next:
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lsr lfsrhi
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ror lfsrlo
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bcc ln_notap
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lda lfsrhi
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eor #$02
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sta lfsrhi
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lda lfsrlo
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eor #$40
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sta lfsrlo
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ln_notap:
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lda lfsrhi ; skip 1000..1023 ($03e8..$03ff)
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cmp #$03
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bcc ln_ok
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lda lfsrlo
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cmp #$e8
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bcs lfsr_next
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ln_ok:
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rts
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; ============================================================
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; TR_WIPE - column sweep, one column per frame, left to right
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; ============================================================
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wipe_in:
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lda #0
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sta wcol
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wi_col:
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jsr wait_frame
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ldx #24
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wi_row:
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lda mul40lo,x
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sta scrlo
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sta collo
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lda mul40hi,x
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clc
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adc #>FADEBUF
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sta scrhi
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lda mul40hi,x
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clc
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adc #>COLRAM
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sta colhi
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ldy wcol
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lda (scrlo),y ; restore the snapshot color
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sta (collo),y
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dex
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bpl wi_row
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inc wcol
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lda wcol
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cmp #40
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bne wi_col
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rts
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wipe_out:
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lda #0
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sta wcol
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wo_col:
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jsr wait_frame
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ldx #24
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wo_row:
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lda mul40lo,x
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sta collo
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lda mul40hi,x
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clc
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adc #>COLRAM
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sta colhi
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ldy wcol
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lda #BLACK
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sta (collo),y
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dex
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bpl wo_row
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inc wcol
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lda wcol
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cmp #40
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bne wo_col
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rts
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; ============================================================
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; shared helpers
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; ============================================================
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; ---- wait for the next bottom-border arrival of the beam ----
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wait_frame:
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wf_leave:
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lda RASTER ; first leave line RAS_BOTTOM if we are on it
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cmp #RAS_BOTTOM
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beq wf_leave
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wf_reach:
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lda RASTER
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cmp #RAS_BOTTOM
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bne wf_reach
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jsr music_play ; advance the music once per frame
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rts
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; ---- copy color RAM to FADEBUF, then blacken color RAM ----
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snapshot_colram:
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ldx #0
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sn_loop:
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lda COLRAM,x
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and #15
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sta FADEBUF,x
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lda COLRAM+250,x
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and #15
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sta FADEBUF+250,x
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lda COLRAM+500,x
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and #15
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sta FADEBUF+500,x
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lda COLRAM+750,x
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and #15
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sta FADEBUF+750,x
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lda #BLACK
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sta COLRAM,x
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sta COLRAM+250,x
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sta COLRAM+500,x
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sta COLRAM+750,x
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inx
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cpx #250
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bne sn_loop
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rts
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; ---- variables ----
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fadecnt: !byte 0 ; fade step counter
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bmcnt: !byte 0 ; build_map inner counter
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curmap: !fill 16, 0 ; current fade-in color map
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lfsrlo: !byte $37 ; LFSR state (any nonzero seed)
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lfsrhi: !byte $01
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cellcnt: !byte 0 ; dissolve: cells left this frame
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frcnt: !byte 0 ; dissolve: frames left
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wcol: !byte 0 ; wipe: current column
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