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mr.zero
2026-07-18 18:34:28 +02:00
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common.asm
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; -----------------------------------------------------------
; common.asm - routines shared by the states: screen drawing,
; text printing, big block font, input and the RNG
; (ported from rabbitc64, trimmed to what this game needs)
; -----------------------------------------------------------
; ---- clear screen RAM, fill color RAM with black ----
clear_screen:
ldx #0
cls_loop:
lda #$20 ; space
sta SCREEN,x
sta SCREEN+$100,x
sta SCREEN+$200,x
sta SCREEN+$2e8,x
lda #BLACK
sta COLRAM,x
sta COLRAM+$100,x
sta COLRAM+$200,x
sta COLRAM+$2e8,x
inx
bne cls_loop
rts
; ---- print a text line: txtlo/hi, prow, pcol, pcolor, plen ----
print_text:
ldx prow
lda mul40lo,x
clc
adc pcol
sta scrlo
sta collo
lda mul40hi,x
adc #>SCREEN ; carry still valid from the low-byte add
sta scrhi
clc
adc #$d4 ; COLRAM - SCREEN high byte distance
sta colhi
ldy #0
pt_loop:
lda (txtlo),y
sta (scrlo),y
lda pcolor
sta (collo),y
iny
cpy plen
bne pt_loop
rts
; ---- set scrlo/hi + collo/hi to the start of char row X ----
row_ptr:
lda mul40lo,x
sta scrlo
sta collo
lda mul40hi,x
clc
adc #>SCREEN
sta scrhi
clc
adc #$d4 ; COLRAM - SCREEN high byte distance
sta colhi
rts
; ---- input ----
; joystick 1 shares the CIA port B lines the keyboard rows use,
; so before any key scan we note which rows the stick itself is
; grounding (jmask) and treat those rows as released - a held
; joystick 1 direction must not read as a phantom keypress
; read joystick port 2 merged with w/a/s/d + space (the runner),
; active-high bits in A and joyb
read_joy:
lda #$ff ; deselect every keyboard column first
sta CIA1_PA
lda CIA1_PB
eor #$ff
and #$1f
sta jmask ; rows grounded by joystick 1 right now
lda CIA1_PA
eor #$ff
and #$1f
sta joyb ; joystick 2 bits
lda #$fd ; keyboard column 1: w / a / s
sta CIA1_PA
lda CIA1_PB
ora jmask
and #$02 ; 'w' = up: row bit 1
bne rj_now
lda joyb
ora #JOY_UP
sta joyb
rj_now:
lda CIA1_PB
ora jmask
and #$04 ; 'a' = left: row bit 2
bne rj_noa
lda joyb
ora #JOY_LEFT
sta joyb
rj_noa:
lda CIA1_PB
ora jmask
and #$20 ; 's' = down: row bit 5
bne rj_nos
lda joyb
ora #JOY_DOWN
sta joyb
rj_nos:
lda #$fb ; 'd' = right: keyboard column 2, row bit 2
sta CIA1_PA
lda CIA1_PB
ora jmask
and #$04
bne rj_nod
lda joyb
ora #JOY_RIGHT
sta joyb
rj_nod:
lda #$7f ; space = fire: keyboard column 7, row bit 4
sta CIA1_PA
lda CIA1_PB
ora jmask
and #$10
bne rj_nosp
lda joyb
ora #JOY_FIRE
sta joyb
rj_nosp:
lda #$ff
sta CIA1_PA
lda joyb
rts
; read joystick port 1 merged with i/j/k/l + return (the wall
; spinner), active-high bits in A and joyb2
read_joy2:
lda #$ff ; no column selected: port B = joystick 1
sta CIA1_PA
lda CIA1_PB
eor #$ff
and #$1f
sta joyb2 ; joystick 1 bits
sta jmask ; ... which also ground the key rows below
lda #$ef ; keyboard column 4: i / j / k
sta CIA1_PA
lda CIA1_PB
ora jmask
and #$02 ; 'i' = up: row bit 1
bne rk_noi
lda joyb2
ora #JOY_UP
sta joyb2
rk_noi:
lda CIA1_PB
ora jmask
and #$04 ; 'j' = left: row bit 2
bne rk_noj
lda joyb2
ora #JOY_LEFT
sta joyb2
rk_noj:
lda CIA1_PB
ora jmask
and #$20 ; 'k' = down: row bit 5
bne rk_nok
lda joyb2
ora #JOY_DOWN
sta joyb2
rk_nok:
lda #$df ; 'l' = right: keyboard column 5, row bit 2
sta CIA1_PA
lda CIA1_PB
ora jmask
and #$04
bne rk_nol
lda joyb2
ora #JOY_RIGHT
sta joyb2
rk_nol:
lda #$fe ; return = fire: keyboard column 0, row bit 1
sta CIA1_PA
lda CIA1_PB
ora jmask
and #$02
bne rk_noret
lda joyb2
ora #JOY_FIRE
sta joyb2
rk_noret:
lda #$ff
sta CIA1_PA
lda joyb2
rts
; fire held on either side? (stick fire, space or return)
; returns A != 0 when pressed
start_pressed:
jsr read_joy
and #JOY_FIRE
bne sp_done
jsr read_joy2
and #JOY_FIRE
sp_done:
rts
; edge-detected start: A = 1 only on the frame fire/space goes down
start_edge:
jsr start_pressed
beq se_up
lda fheld
bne se_no
lda #1
sta fheld
rts ; A = 1: fresh press
se_up:
lda #0
sta fheld
se_no:
lda #0
rts
; ---- RNG: 8-bit LFSR stirred with the free-running CIA timer
; (the timer counts every cycle, so call timing = entropy) ----
rand8:
lda seed
asl
bcc r8_tap
eor #$1d
r8_tap:
eor CIA1_TA
sta seed
rts
; ---- draw a text line with big 3x5 block letters ----
; txtlo/hi = text (screen codes), bigrow/bigcol = top-left cell,
; bigcolor = color, biglen = char count; each letter is 3 cells
; wide + 1 gap, 5 cells tall
draw_big:
lda #0
sta bigi
db_char:
ldy bigi
lda (txtlo),y
cmp #$20 ; space: leave the cell empty
beq db_next
tax
lda bigmap,x ; screen code -> glyph index
sta glyphbase
asl ; glyph base = index * 5
asl
clc
adc glyphbase
sta glyphbase
lda bigi ; cell x = bigcol + charindex * 4
asl
asl
clc
adc bigcol
sta charx
lda #0
sta rowidx
db_row:
lda bigrow ; row pointers from the row*40 tables
clc
adc rowidx
tax
lda mul40lo,x
sta scrlo
sta collo
lda mul40hi,x
clc
adc #>SCREEN
sta scrhi
clc
adc #$d4
sta colhi
lda glyphbase
clc
adc rowidx
tax
lda bigglyphs,x
asl ; 3-bit pattern up to bits 7-5
asl
asl
asl
asl
sta curbits
ldy charx
lda #3
sta bitcnt
db_bit:
asl curbits ; leftmost pixel first
bcc db_nobit
lda #$a0 ; inverse space = solid block
sta (scrlo),y
lda bigcolor
sta (collo),y
db_nobit:
iny
dec bitcnt
bne db_bit
inc rowidx
lda rowidx
cmp #5
bne db_row
db_next:
inc bigi
lda bigi
cmp biglen
beq db_done
jmp db_char ; too far for a relative branch
db_done:
rts
; ---- shared tables ----
; row * 40 lookup tables (25 rows)
mul40lo:
!byte $00, $28, $50, $78, $a0, $c8, $f0, $18, $40, $68
!byte $90, $b8, $e0, $08, $30, $58, $80, $a8, $d0, $f8
!byte $20, $48, $70, $98, $c0
mul40hi:
!byte $00, $00, $00, $00, $00, $00, $00, $01, $01, $01
!byte $01, $01, $01, $02, $02, $02, $02, $02, $02, $02
!byte $03, $03, $03, $03, $03
; 3x5 block font for the big titles (5 bytes per glyph,
; low 3 bits used, MSB side = left)
bigglyphs:
!byte 0, 0, 0, 0, 0 ; 0 space
!byte 2, 5, 7, 5, 5 ; 1 A
!byte 3, 4, 4, 4, 3 ; 2 C
!byte 6, 5, 5, 5, 6 ; 3 D
!byte 7, 4, 6, 4, 7 ; 4 E
!byte 7, 4, 6, 4, 4 ; 5 F
!byte 7, 2, 2, 2, 7 ; 6 I
!byte 4, 4, 4, 4, 7 ; 7 L
!byte 5, 7, 7, 5, 5 ; 8 M
!byte 6, 5, 5, 5, 5 ; 9 N
!byte 7, 5, 5, 5, 7 ; 10 O
!byte 6, 5, 6, 4, 4 ; 11 P
!byte 6, 5, 6, 5, 5 ; 12 R
!byte 3, 4, 2, 1, 6 ; 13 S
!byte 7, 2, 2, 2, 2 ; 14 T
!byte 5, 5, 2, 2, 2 ; 15 Y
!byte 3, 4, 5, 5, 7 ; 16 G
!byte 6, 5, 6, 5, 6 ; 17 B
!byte 5, 5, 5, 5, 2 ; 18 V
!byte 5, 5, 7, 5, 5 ; 19 H
!byte 5, 5, 5, 5, 7 ; 20 U
!byte 5, 5, 7, 7, 5 ; 21 W
bigmap: ; screen code (a=1..z=26) -> glyph index
!byte 0 ; (unused)
!byte 1, 17, 2, 3, 4, 5, 16, 19, 6, 0 ; a-j
!byte 0, 7, 8, 9, 10, 11, 0, 12, 13, 14 ; k-t
!byte 20, 18, 21, 0, 15, 0 ; u-z
; ---- shared texts (screen codes) ----
txt_title: !scr "labyrinth"
txt_ttgname: !scr "teletype games"
txt_presents:!scr "presents"
txt_return: !scr "fire = return"
txt_blank: !fill 16, $20
washtbl: ; gold glow ramp (16 entries, cyclic)
!byte $09, $02, $08, $0a, $07, $07, $01, $01
!byte $01, $01, $07, $07, $0a, $08, $02, $09
; ---- shared variables ----
framectr: !byte 0 ; frame counter, incremented by the main loop
washphase: !byte 0 ; gold wash offset on the big letters
seed: !byte $a7 ; rand8 LFSR state
fheld: !byte 0 ; fire/space edge detection state
joyb: !byte 0 ; player 1 input bits from read_joy
joyb2: !byte 0 ; player 2 input bits from read_joy2
jmask: !byte 0 ; key rows grounded by joystick 1 this scan
prow: !byte 0 ; print_text: row, column, color, length
pcol: !byte 0
pcolor: !byte 0
plen: !byte 0
bigrow: !byte 0 ; draw_big: row, column, color, length
bigcol: !byte 0
bigcolor: !byte 0
biglen: !byte 0
bigi: !byte 0 ; draw_big internals
glyphbase: !byte 0
charx: !byte 0
rowidx: !byte 0
bitcnt: !byte 0
curbits: !byte 0
rtmp: !byte 0 ; scratch
rtmp2: !byte 0