434 lines
10 KiB
NASM
434 lines
10 KiB
NASM
; -----------------------------------------------------------
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; common.asm - routines shared by the states: screen drawing,
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; text printing, big block font, input and the RNG
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; (ported from rabbitc64, trimmed to what this game needs)
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; -----------------------------------------------------------
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; ---- clear screen RAM, fill color RAM with black ----
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clear_screen:
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ldx #0
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cls_loop:
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lda #$20 ; space
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sta SCREEN,x
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sta SCREEN+$100,x
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sta SCREEN+$200,x
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sta SCREEN+$2e8,x
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lda #BLACK
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sta COLRAM,x
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sta COLRAM+$100,x
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sta COLRAM+$200,x
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sta COLRAM+$2e8,x
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inx
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bne cls_loop
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rts
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; ---- print a text line: txtlo/hi, prow, pcol, pcolor, plen ----
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print_text:
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ldx prow
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lda mul40lo,x
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clc
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adc pcol
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sta scrlo
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sta collo
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lda mul40hi,x
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adc #>SCREEN ; carry still valid from the low-byte add
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sta scrhi
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clc
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adc #$d4 ; COLRAM - SCREEN high byte distance
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sta colhi
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ldy #0
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pt_loop:
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lda (txtlo),y
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sta (scrlo),y
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lda pcolor
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sta (collo),y
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iny
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cpy plen
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bne pt_loop
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rts
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; ---- set scrlo/hi + collo/hi to the start of char row X ----
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row_ptr:
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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 #>SCREEN
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sta scrhi
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clc
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adc #$d4 ; COLRAM - SCREEN high byte distance
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sta colhi
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rts
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; ---- input ----
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; joystick 1 shares the CIA port B lines the keyboard rows use,
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; so before any key scan we note which rows the stick itself is
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; grounding (jmask) and treat those rows as released - a held
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; joystick 1 direction must not read as a phantom keypress
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; read joystick port 2 merged with w/a/s/d + space (the runner),
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; active-high bits in A and joyb
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read_joy:
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lda #$ff ; deselect every keyboard column first
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sta CIA1_PA
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lda CIA1_PB
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eor #$ff
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and #$1f
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sta jmask ; rows grounded by joystick 1 right now
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lda CIA1_PA
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eor #$ff
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and #$1f
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sta joyb ; joystick 2 bits
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lda #$fd ; keyboard column 1: w / a / s
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sta CIA1_PA
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lda CIA1_PB
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ora jmask
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and #$02 ; 'w' = up: row bit 1
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bne rj_now
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lda joyb
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ora #JOY_UP
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sta joyb
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rj_now:
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lda CIA1_PB
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ora jmask
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and #$04 ; 'a' = left: row bit 2
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bne rj_noa
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lda joyb
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ora #JOY_LEFT
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sta joyb
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rj_noa:
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lda CIA1_PB
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ora jmask
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and #$20 ; 's' = down: row bit 5
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bne rj_nos
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lda joyb
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ora #JOY_DOWN
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sta joyb
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rj_nos:
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lda #$fb ; 'd' = right: keyboard column 2, row bit 2
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sta CIA1_PA
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lda CIA1_PB
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ora jmask
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and #$04
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bne rj_nod
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lda joyb
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ora #JOY_RIGHT
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sta joyb
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rj_nod:
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lda #$7f ; space = fire: keyboard column 7, row bit 4
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sta CIA1_PA
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lda CIA1_PB
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ora jmask
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and #$10
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bne rj_nosp
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lda joyb
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ora #JOY_FIRE
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sta joyb
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rj_nosp:
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lda #$ff
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sta CIA1_PA
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lda joyb
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rts
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; read joystick port 1 merged with i/j/k/l + return (the wall
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; spinner), active-high bits in A and joyb2
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read_joy2:
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lda #$ff ; no column selected: port B = joystick 1
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sta CIA1_PA
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lda CIA1_PB
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eor #$ff
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and #$1f
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sta joyb2 ; joystick 1 bits
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sta jmask ; ... which also ground the key rows below
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lda #$ef ; keyboard column 4: i / j / k
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sta CIA1_PA
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lda CIA1_PB
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ora jmask
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and #$02 ; 'i' = up: row bit 1
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bne rk_noi
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lda joyb2
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ora #JOY_UP
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sta joyb2
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rk_noi:
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lda CIA1_PB
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ora jmask
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and #$04 ; 'j' = left: row bit 2
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bne rk_noj
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lda joyb2
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ora #JOY_LEFT
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sta joyb2
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rk_noj:
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lda CIA1_PB
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ora jmask
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and #$20 ; 'k' = down: row bit 5
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bne rk_nok
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lda joyb2
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ora #JOY_DOWN
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sta joyb2
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rk_nok:
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lda #$df ; 'l' = right: keyboard column 5, row bit 2
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sta CIA1_PA
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lda CIA1_PB
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ora jmask
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and #$04
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bne rk_nol
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lda joyb2
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ora #JOY_RIGHT
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sta joyb2
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rk_nol:
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lda #$fe ; return = fire: keyboard column 0, row bit 1
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sta CIA1_PA
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lda CIA1_PB
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ora jmask
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and #$02
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bne rk_noret
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lda joyb2
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ora #JOY_FIRE
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sta joyb2
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rk_noret:
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lda #$ff
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sta CIA1_PA
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lda joyb2
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rts
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; fire held on either side? (stick fire, space or return)
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; returns A != 0 when pressed
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start_pressed:
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jsr read_joy
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and #JOY_FIRE
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bne sp_done
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jsr read_joy2
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and #JOY_FIRE
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sp_done:
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rts
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; edge-detected start: A = 1 only on the frame fire/space goes down
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start_edge:
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jsr start_pressed
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beq se_up
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lda fheld
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bne se_no
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lda #1
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sta fheld
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rts ; A = 1: fresh press
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se_up:
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lda #0
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sta fheld
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se_no:
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lda #0
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rts
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; ---- RNG: 8-bit LFSR stirred with the free-running CIA timer
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; (the timer counts every cycle, so call timing = entropy) ----
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rand8:
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lda seed
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asl
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bcc r8_tap
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eor #$1d
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r8_tap:
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eor CIA1_TA
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sta seed
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rts
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; ---- draw a text line with big 3x5 block letters ----
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; txtlo/hi = text (screen codes), bigrow/bigcol = top-left cell,
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; bigcolor = color, biglen = char count; each letter is 3 cells
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; wide + 1 gap, 5 cells tall
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draw_big:
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lda #0
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sta bigi
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db_char:
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ldy bigi
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lda (txtlo),y
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cmp #$20 ; space: leave the cell empty
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beq db_next
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tax
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lda bigmap,x ; screen code -> glyph index
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sta glyphbase
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asl ; glyph base = index * 5
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asl
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clc
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adc glyphbase
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sta glyphbase
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lda bigi ; cell x = bigcol + charindex * 4
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asl
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asl
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clc
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adc bigcol
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sta charx
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lda #0
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sta rowidx
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db_row:
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lda bigrow ; row pointers from the row*40 tables
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clc
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adc rowidx
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tax
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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 #>SCREEN
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sta scrhi
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clc
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adc #$d4
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sta colhi
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lda glyphbase
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clc
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adc rowidx
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tax
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lda bigglyphs,x
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asl ; 3-bit pattern up to bits 7-5
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asl
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asl
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asl
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asl
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sta curbits
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ldy charx
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lda #3
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sta bitcnt
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db_bit:
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asl curbits ; leftmost pixel first
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bcc db_nobit
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lda #$a0 ; inverse space = solid block
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sta (scrlo),y
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lda bigcolor
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sta (collo),y
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db_nobit:
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iny
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dec bitcnt
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bne db_bit
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inc rowidx
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lda rowidx
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cmp #5
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bne db_row
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db_next:
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inc bigi
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lda bigi
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cmp biglen
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beq db_done
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jmp db_char ; too far for a relative branch
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db_done:
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rts
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; ---- shared tables ----
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; row * 40 lookup tables (25 rows)
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mul40lo:
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!byte $00, $28, $50, $78, $a0, $c8, $f0, $18, $40, $68
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!byte $90, $b8, $e0, $08, $30, $58, $80, $a8, $d0, $f8
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!byte $20, $48, $70, $98, $c0
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mul40hi:
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!byte $00, $00, $00, $00, $00, $00, $00, $01, $01, $01
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!byte $01, $01, $01, $02, $02, $02, $02, $02, $02, $02
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!byte $03, $03, $03, $03, $03
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; 3x5 block font for the big titles (5 bytes per glyph,
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; low 3 bits used, MSB side = left)
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bigglyphs:
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!byte 0, 0, 0, 0, 0 ; 0 space
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!byte 2, 5, 7, 5, 5 ; 1 A
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!byte 3, 4, 4, 4, 3 ; 2 C
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!byte 6, 5, 5, 5, 6 ; 3 D
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!byte 7, 4, 6, 4, 7 ; 4 E
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!byte 7, 4, 6, 4, 4 ; 5 F
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!byte 7, 2, 2, 2, 7 ; 6 I
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!byte 4, 4, 4, 4, 7 ; 7 L
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!byte 5, 7, 7, 5, 5 ; 8 M
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!byte 6, 5, 5, 5, 5 ; 9 N
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!byte 7, 5, 5, 5, 7 ; 10 O
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!byte 6, 5, 6, 4, 4 ; 11 P
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!byte 6, 5, 6, 5, 5 ; 12 R
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!byte 3, 4, 2, 1, 6 ; 13 S
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!byte 7, 2, 2, 2, 2 ; 14 T
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!byte 5, 5, 2, 2, 2 ; 15 Y
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!byte 3, 4, 5, 5, 7 ; 16 G
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!byte 6, 5, 6, 5, 6 ; 17 B
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!byte 5, 5, 5, 5, 2 ; 18 V
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!byte 5, 5, 7, 5, 5 ; 19 H
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!byte 5, 5, 5, 5, 7 ; 20 U
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!byte 5, 5, 7, 7, 5 ; 21 W
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bigmap: ; screen code (a=1..z=26) -> glyph index
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!byte 0 ; (unused)
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!byte 1, 17, 2, 3, 4, 5, 16, 19, 6, 0 ; a-j
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!byte 0, 7, 8, 9, 10, 11, 0, 12, 13, 14 ; k-t
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!byte 20, 18, 21, 0, 15, 0 ; u-z
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; ---- gold wash over the two big title lines (rows 1-5 and
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; 7-11): only the $a0 letter blocks are recolored, so it is
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; safe over any backdrop ----
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wash_title:
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inc washphase
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lda #0
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sta g8row
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wt_row:
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ldx g8row
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lda wtrows,x
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tax
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jsr row_ptr
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lda washphase
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lsr ; half speed keeps the shimmer gentle
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clc
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adc g8row
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and #15
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tax
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lda washtbl,x
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sta rtmp
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ldy #39
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wt_col:
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lda (scrlo),y
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cmp #$a0 ; only touch the letter blocks
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bne wt_skip
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lda rtmp
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sta (collo),y
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wt_skip:
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dey
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bpl wt_col
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inc g8row
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lda g8row
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cmp #10
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bne wt_row
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rts
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wtrows: !byte 1, 2, 3, 4, 5, 7, 8, 9, 10, 11
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; ---- shared texts (screen codes) ----
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; the title is split so the two lines can be placed apart
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txt_t1: !scr "blessing"
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txt_t2: !scr "of ra"
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txt_ttgname: !scr "teletype games"
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txt_presents:!scr "presents"
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txt_return: !scr "fire = return"
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txt_blank: !fill 16, $20
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washtbl: ; gold glow ramp (16 entries, cyclic)
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!byte $09, $02, $08, $0a, $07, $07, $01, $01
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!byte $01, $01, $07, $07, $0a, $08, $02, $09
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; ---- shared variables ----
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framectr: !byte 0 ; frame counter, incremented by the main loop
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washphase: !byte 0 ; gold wash offset on the big letters
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seed: !byte $a7 ; rand8 LFSR state
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fheld: !byte 0 ; fire/space edge detection state
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joyb: !byte 0 ; player 1 input bits from read_joy
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joyb2: !byte 0 ; player 2 input bits from read_joy2
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jmask: !byte 0 ; key rows grounded by joystick 1 this scan
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prow: !byte 0 ; print_text: row, column, color, length
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pcol: !byte 0
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pcolor: !byte 0
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plen: !byte 0
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bigrow: !byte 0 ; draw_big: row, column, color, length
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bigcol: !byte 0
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bigcolor: !byte 0
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biglen: !byte 0
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bigi: !byte 0 ; draw_big internals
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glyphbase: !byte 0
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charx: !byte 0
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rowidx: !byte 0
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bitcnt: !byte 0
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curbits: !byte 0
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rtmp: !byte 0 ; scratch
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rtmp2: !byte 0
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