extra effects

slide4.asm

@@ -1,6 +1,8 @@
 ; -----------------------------------------------------------
 ; slide4.asm - CONTACT
-;   pulsing big title, contact lines below
+;   pulsing big title, contact lines, three-layer starfield
+;   drifting left, six star sprites floating on sine paths
+;   behind the text
 ; -----------------------------------------------------------
 
 s4_init:
@@ -9,6 +11,43 @@ s4_init:
     +prtext 10,  7, LGREEN, txt_web, txt_web_end - txt_web
     +prtext 13,  6, YELLOW, txt_bbs, txt_bbs_end - txt_bbs
     +prtext 16,  4, CYAN,   txt_irc, txt_irc_end - txt_irc
+
+    ; starfield: draw the stars at their current positions so
+    ; the in-transition reveals them together with the text
+    ldx #11
+s4i_star:
+    jsr star_ptr
+    ldy star_x,x
+    lda #$2e             ; '.'
+    sta (scrlo),y
+    lda star_col,x
+    sta (collo),y
+    dex
+    bpl s4i_star
+
+    ; sprites: same star shape on all six, floating behind the
+    ; characters; enabled by the update, so they pop in only
+    ; after the slide's in-transition is done
+    lda #(sprdata >> 6)
+    ldx #5
+s4i_ptr:
+    sta SCREEN+$3f8,x
+    dex
+    bpl s4i_ptr
+    ldx #5
+s4i_col:
+    lda sprcols,x
+    sta SPR_COL,x
+    dex
+    bpl s4i_col
+    lda #0
+    sta SPR_MC
+    sta SPR_XEX
+    sta SPR_YEX
+    lda #%00111111
+    sta SPR_PRIO         ; behind the text
+    lda #%00100000       ; sprite 5 lives right of x=255
+    sta SPR_MSBX
     rts
 
 s4_update:
@@ -33,6 +72,79 @@ s4_loop:
     sta COLRAM + 6*40,x
     dex
     bpl s4_loop
+
+    ; starfield: three layers, each layer steps left on its own
+    ; frame mask (fast/mid/slow parallax)
+    ldx #11
+s4u_star:
+    lda framectr
+    and star_mask,x
+    bne s4u_next
+    jsr star_ptr
+    ldy star_x,x
+    lda #$20             ; erase at the old position
+    sta (scrlo),y
+    lda star_x,x         ; step left, wrap at the edge
+    bne s4u_dec
+    lda #40
+    sta star_x,x
+s4u_dec:
+    dec star_x,x
+    ldy star_x,x
+    lda #$2e
+    sta (scrlo),y
+    lda star_col,x
+    sta (collo),y
+s4u_next:
+    dex
+    bpl s4u_star
+
+    ; sprites: y from a sine table, x = base + slower sine wobble
+    lda #%00111111
+    sta SPR_EN
+    ldx #5
+s4u_spr:
+    txa
+    asl
+    sta sprofs           ; register offset = sprite * 2
+    lda framectr
+    lsr
+    clc
+    adc spr_yph,x
+    and #63
+    tay
+    lda ysin,y
+    ldy sprofs
+    sta SPRPOS+1,y
+    lda framectr
+    lsr
+    lsr
+    clc
+    adc spr_xph,x
+    and #63
+    tay
+    lda xwob,y
+    clc
+    adc spr_xbase,x
+    ldy sprofs
+    sta SPRPOS,y
+    dex
+    bpl s4u_spr
+    rts
+
+; ---- scrlo/hi + collo/hi = screen/color RAM row of star X ----
+star_ptr:
+    ldy star_row,x
+    lda mul40lo,y
+    sta scrlo
+    sta collo
+    lda mul40hi,y
+    clc
+    adc #>SCREEN
+    sta scrhi
+    clc
+    adc #$d4             ; COLRAM - SCREEN high byte distance
+    sta colhi
     rts
 
 ; ---- data ----
@@ -47,3 +159,72 @@ txt_bbs_end:
 txt_irc:
     !scr "irc: libera.chat #teletypegames"
 txt_irc_end:
+
+; starfield: rows avoid the title (2-6) and text (10, 13, 16) rows
+star_row:
+    !byte  0,  8, 11, 14, 17, 19,  1,  9, 12, 15, 21, 23
+star_mask:               ; move on framectr & mask == 0
+    !byte  1,  3,  7,  1,  3,  7,  1,  3,  7,  1,  3,  7
+star_col:                ; fast = white, mid = lgrey, slow = dgrey
+    !byte WHITE, LGREY, DGREY, WHITE, LGREY, DGREY
+    !byte WHITE, LGREY, DGREY, WHITE, LGREY, DGREY
+
+sprcols:
+    !byte YELLOW, LBLUE, LGREEN, WHITE, ORANGE, CYAN
+spr_xbase:               ; spread across the screen; sprite 5 gets
+    !byte 40, 85, 130, 175, 220, 20   ;   +256 via SPR_MSBX
+spr_yph:                 ; sine phase offsets per sprite
+    !byte  0, 11, 21, 32, 43, 53
+spr_xph:
+    !byte  0, 26, 52, 13, 39,  7
+
+ysin:                    ; 64-entry sine, 134 +/- 60 (sprite y)
+    !byte $86, $8c, $92, $97, $9d, $a2, $a7, $ac
+    !byte $b0, $b4, $b8, $bb, $bd, $bf, $c1, $c2
+    !byte $c2, $c2, $c1, $bf, $bd, $bb, $b8, $b4
+    !byte $b0, $ac, $a7, $a2, $9d, $97, $92, $8c
+    !byte $86, $80, $7a, $75, $6f, $6a, $65, $60
+    !byte $5c, $58, $54, $51, $4f, $4d, $4b, $4a
+    !byte $4a, $4a, $4b, $4d, $4f, $51, $54, $58
+    !byte $5c, $60, $65, $6a, $6f, $75, $7a, $80
+
+xwob:                    ; 64-entry sine, 12 +/- 12 (x wobble)
+    !byte $0c, $0d, $0e, $0f, $11, $12, $13, $14
+    !byte $14, $15, $16, $17, $17, $17, $18, $18
+    !byte $18, $18, $18, $17, $17, $17, $16, $15
+    !byte $14, $14, $13, $12, $11, $0f, $0e, $0d
+    !byte $0c, $0b, $0a, $09, $07, $06, $05, $04
+    !byte $04, $03, $02, $01, $01, $01, $00, $00
+    !byte $00, $00, $00, $01, $01, $01, $02, $03
+    !byte $04, $04, $05, $06, $07, $09, $0a, $0b
+
+; 24x21 four-pointed star sprite (must sit on a 64-byte boundary
+; and below $4000, the top of the VIC's bank)
+!align 63, 0
+sprdata:
+    !byte $00, $00, $00
+    !byte $00, $00, $00
+    !byte $00, $18, $00
+    !byte $00, $18, $00
+    !byte $00, $18, $00
+    !byte $00, $3c, $00
+    !byte $00, $3c, $00
+    !byte $00, $7e, $00
+    !byte $07, $ff, $e0
+    !byte $00, $7e, $00
+    !byte $00, $3c, $00
+    !byte $00, $3c, $00
+    !byte $00, $18, $00
+    !byte $00, $18, $00
+    !byte $00, $18, $00
+    !byte $00, $00, $00
+    !byte $00, $00, $00
+    !byte $00, $00, $00
+    !byte $00, $00, $00
+    !byte $00, $00, $00
+    !byte $00, $00, $00
+
+; ---- variables ----
+star_x:                  ; star columns (start scattered)
+    !byte  3, 17, 29,  8, 35, 22, 13, 31,  5, 26, 19, 37
+sprofs:    !byte 0       ; sprite register offset in the update loop