multiplayer support

README.md

@@ -10,12 +10,18 @@ that passes in any other lane is a **point**. Three misses end the round.
 The spawn rate and the rabbits' speed ramp up with your score, just like
 in the original.
 
+In **multiplayer** the rabbits still spawn on their own, but player 2
+steers the closest one left and right, trying to run the scooter down.
+
 ## Controls
 
 | Input | Action |
 |-------|--------|
-| Joystick port 2 left/right, or `A` / `D` | change lane (auto-repeats while held) |
+| Menu: joystick up/down, or the `S` / `M` keys | pick single player / multiplayer |
-| Fire (or `SPACE`) | start / retry |
+| Menu: fire (or `SPACE`); the `1` / `2` keys pick and start at once | start the picked mode |
+| P1: joystick port 2 left/right, or `A` / `D` | move the scooter (auto-repeats while held) |
+| P2: joystick port 1 left/right, or `J` / `L` | steer the closest rabbit (multiplayer) |
+| Fire (or `SPACE`) | start; on the game over screen: back to the menu |
 
 ## How it works
 

common.asm

@@ -206,11 +206,49 @@ rj_noright:
     lda joyb
     rts
 
-; fire or space held? returns A != 0 when pressed
+; read joystick port 1 merged with the j/l keys (player 2),
+; return 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
+    and #$0f             ; a held direction grounds the same port B
+    bne rj2_done         ;   lines the key rows use: skip the scan
+    lda #$ef             ; 'j' = left: keyboard column 4, row bit 2
+    sta CIA1_PA
+    lda CIA1_PB
+    and #$04
+    bne rj2_noleft
+    lda joyb2
+    ora #JOY_LEFT
+    sta joyb2
+rj2_noleft:
+    lda #$df             ; 'l' = right: keyboard column 5, row bit 2
+    sta CIA1_PA
+    lda CIA1_PB
+    and #$04
+    bne rj2_done
+    lda joyb2
+    ora #JOY_RIGHT
+    sta joyb2
+rj2_done:
+    lda joyb2
+    rts
+
+; fire on either stick or space held? returns A != 0 when pressed
 start_pressed:
     jsr read_joy
     and #JOY_FIRE
     bne sp_done
+    lda #$ff             ; deselect the columns: port B = joystick 1
+    sta CIA1_PA
+    lda CIA1_PB
+    eor #$ff
+    and #JOY_FIRE
+    bne sp_done
     lda #$7f             ; space: keyboard column 7, row bit 4
     sta CIA1_PA
     lda CIA1_PB
@@ -546,12 +584,14 @@ txt_score:   !scr "score"
 txt_miss:    !scr "miss"
 txt_rabbit:  !scr "rabbit"
 txt_scooter: !scr "scooter"
-txt_press:   !scr "fire = start game"
+txt_1p:      !scr "single player"
-txt_info:    !scr "joystick 2 or a/d moves"
+txt_2p:      !scr "multiplayer"
+txt_info:    !scr "p1: joystick 2 or a/d"
+txt_info2:   !scr "p2: joystick 1 or j/l"
 txt_ttgname: !scr "teletype games"
 txt_presents:!scr "presents"
 txt_over:    !scr "game over"
-txt_retry:   !scr "fire = retry"
+txt_return:  !scr "fire = return"
 txt_blank:   !fill 19, $20
 
 washtbl:                 ; gold glow ramp (16 entries, cyclic)
@@ -565,7 +605,10 @@ bg_top:    !byte COL_SKY ; background color above / below the
 bg_bot:    !byte COL_GRASS   ; horizon raster split
 seed:      !byte $a7     ; rand8 LFSR state
 fheld:     !byte 0       ; fire/space edge detection state
-joyb:      !byte 0       ; joystick bits from read_joy (active high)
+joyb:      !byte 0       ; player 1 input bits from read_joy
+joyb2:     !byte 0       ; player 2 input bits from read_joy2
+mp_mode:   !byte 0       ; 0 = single player, 1 = multiplayer
+k12held:   !byte 0       ; menu '1'/'2' key edge detection state
 en_sh:     !byte 0       ; per-frame sprite register shadows
 msb_sh:    !byte 0
 xex_sh:    !byte 0

over.asm

@@ -32,17 +32,17 @@ over_init:
     rts
 
 over_update:
-    ; blink the retry prompt
+    ; blink the return prompt
     lda framectr
     and #32
     bne ou_hide
-    +prtext 16, 14, YELLOW, txt_retry, 12
+    +prtext 16, 13, YELLOW, txt_return, 13
     jmp ou_start
 ou_hide:
-    +prtext 16, 14, YELLOW, txt_blank, 12
+    +prtext 16, 13, YELLOW, txt_blank, 13
 ou_start:
     jsr start_edge
     beq ou_done
-    jmp play_init        ; its rts returns to the main loop
+    jmp title_init       ; back to the menu, mode can be re-picked
 ou_done:
     rts

play.asm

@@ -27,6 +27,8 @@ play_init:
     sta spawnt
     sta lcnt
     sta rcnt
+    sta p2lcnt
+    sta p2rcnt
     jsr draw_score
 
     lda #0               ; draw_score leaves a digit code in A
@@ -113,6 +115,52 @@ pu_rrel:
     sta rcnt
 pu_rend:
 
+    ; -- multiplayer: player 2 steers the closest rabbit --
+    lda mp_mode
+    beq pu_nop2
+    jsr read_joy2
+    lda joyb2
+    and #JOY_LEFT
+    beq pu_p2lrel
+    inc p2lcnt
+    lda p2lcnt
+    cmp #1
+    beq pu_p2lmove
+    cmp #REP_HOLD+REP_PERIOD
+    bne pu_p2lend
+    lda #REP_HOLD
+    sta p2lcnt
+pu_p2lmove:
+    lda #$ff             ; one lane to the left
+    sta rtmp2
+    jsr steer_closest
+    jmp pu_p2lend
+pu_p2lrel:
+    lda #0
+    sta p2lcnt
+pu_p2lend:
+    lda joyb2
+    and #JOY_RIGHT
+    beq pu_p2rrel
+    inc p2rcnt
+    lda p2rcnt
+    cmp #1
+    beq pu_p2rmove
+    cmp #REP_HOLD+REP_PERIOD
+    bne pu_p2rend
+    lda #REP_HOLD
+    sta p2rcnt
+pu_p2rmove:
+    lda #1               ; one lane to the right
+    sta rtmp2
+    jsr steer_closest
+    jmp pu_p2rend
+pu_p2rrel:
+    lda #0
+    sta p2rcnt
+pu_p2rend:
+pu_nop2:
+
     ; -- shadow init: player sprite bit + its x MSB --
     ldx player_lane
     lda pxlo,x
@@ -197,6 +245,36 @@ pu_rnext:
 pu_done:
     rts
 
+; ---- shift the closest live rabbit's lane by rtmp2 (+/-1) ----
+steer_closest:
+    ldx #$ff             ; best slot so far
+    lda #0
+    sta rtmp             ; best t so far
+    ldy #NRABBITS-1
+stc_find:
+    lda r_act,y
+    beq stc_next
+    lda r_thi,y
+    cmp rtmp
+    bcc stc_next
+    sta rtmp
+    tya
+    tax
+stc_next:
+    dey
+    bpl stc_find
+    cpx #$ff
+    beq stc_done         ; no rabbit on the road
+    lda r_lane,x
+    clc
+    adc rtmp2
+    bmi stc_done         ; already on the leftmost lane
+    cmp #LANES
+    bcs stc_done         ; ... or the rightmost one
+    sta r_lane,x
+stc_done:
+    rts
+
 ; ---- claim a free rabbit slot and roll its lane + speed ----
 spawn_rabbit:
     ldx #NRABBITS-1
@@ -298,6 +376,8 @@ flash:       !byte 0     ; frames left of the post-hit blink
 spawnt:      !byte 0     ; frames since the last spawn
 lcnt:        !byte 0     ; held-direction counters for the auto-repeat
 rcnt:        !byte 0
+p2lcnt:      !byte 0     ; the same for player 2's steering
+p2rcnt:      !byte 0
 
 ; ---- rabbit slots (hardware sprites 1-7) ----
 r_act:  !fill NRABBITS, 0

title.asm

@@ -1,7 +1,7 @@
 ; -----------------------------------------------------------
 ; title.asm - full-screen menu card: big RABBIT / SCOOTER
-; logo flanked by two hopping rabbits, the scooter waiting at
+; logo flanked by two hopping rabbits, single/multiplayer
-; the bottom, blinking "fire = start game"
+; picker (joystick up/down + fire, or the 1 / 2 keys)
 ; -----------------------------------------------------------
 
 title_init:
@@ -12,7 +12,8 @@ title_init:
 
     +prbig 2, 8, RED, txt_rabbit, 6
     +prbig 8, 6, WHITE, txt_scooter, 7
-    +prtext 18, 8, WHITE, txt_info, 23
+    +prtext 18, 9, LGREY, txt_info, 21
+    +prtext 19, 9, LGREY, txt_info2, 21
 
     ; decoration: white rabbits flank the logo (sprites 1-2,
     ; double-sized), the red scooter waits at the bottom
@@ -65,17 +66,99 @@ title_update:
     adc #SPRP_BIG
     sta SPRPTR+2
 
-    ; blink the start line
+    ; joystick up/down picks the mode
+    jsr read_joy
+    lda joyb
+    and #1               ; up
+    beq tu_noup
+    lda #0
+    sta mp_mode
+tu_noup:
+    lda joyb
+    and #2               ; down
+    beq tu_nodown
+    lda #1
+    sta mp_mode
+tu_nodown:
+
+    ; the 's' / 'm' keys pick the mode (fire still starts)
+    lda #$fd             ; 's': keyboard column 1, row bit 5
+    sta CIA1_PA
+    lda CIA1_PB
+    and #$20
+    bne tu_nos
+    lda #0
+    sta mp_mode
+tu_nos:
+    lda #$ef             ; 'm': keyboard column 4, row bit 4
+    sta CIA1_PA
+    lda CIA1_PB
+    and #$10
+    bne tu_nom
+    lda #1
+    sta mp_mode
+tu_nom:
+
+    ; the 1 / 2 keys pick and start right away (edge detected)
+    lda #$7f             ; keyboard column 7: '1' = bit 0, '2' = bit 3
+    sta CIA1_PA
+    lda CIA1_PB
+    and #$09
+    cmp #$09
+    beq tu_keyup         ; neither key held
+    ldx k12held
+    bne tu_menu          ; still held from an earlier frame
+    inx
+    stx k12held
+    and #$01
+    bne tu_key2
+    lda #0
+    sta mp_mode
+    jmp title_go
+tu_key2:
+    lda #1
+    sta mp_mode
+    jmp title_go
+tu_keyup:
+    lda #0
+    sta k12held
+tu_menu:
+
+    ; the two options: the picked line is yellow
+    lda mp_mode
+    bne tm_multi
+    +prtext 14, 14, YELLOW, txt_1p, 13
+    +prtext 16, 14, WHITE, txt_2p, 11
+    jmp tm_cursor
+tm_multi:
+    +prtext 14, 14, WHITE, txt_1p, 13
+    +prtext 16, 14, YELLOW, txt_2p, 11
+tm_cursor:
+    ; blinking '>' cursor in front of the picked line
+    lda #$20
+    sta SCREEN+14*40+12
+    sta SCREEN+16*40+12
     lda framectr
-    and #32
+    and #16
-    bne tu_hide
+    bne tu_start
-    +prtext 15, 11, YELLOW, txt_press, 17
+    lda mp_mode
+    bne tm_cur2
+    lda #62              ; '>'
+    sta SCREEN+14*40+12
+    lda #YELLOW
+    sta COLRAM+14*40+12
     jmp tu_start
-tu_hide:
+tm_cur2:
-    +prtext 15, 11, YELLOW, txt_blank, 17
+    lda #62
+    sta SCREEN+16*40+12
+    lda #YELLOW
+    sta COLRAM+16*40+12
+
 tu_start:
+    ; fire or space starts the picked mode
     jsr start_edge
     beq tu_done
+title_go:
     jmp play_init        ; its rts returns to the main loop
 tu_done:
     rts