Darryl's connect 4

;; Darryl Sloan's finished Connect 4
; https://www.youtube.com/watch?v=uWqdk-1_NIg
; 5/7/2017
; https://gist.github.com/robsoft/96260761d30377be67ebf807d0a04397


          org 50000
last_k    equ 23560

          ld hl, udgs
          ld (23675), hl

          ld a, 2
          call 5633

; draw game title
          ld de, banner
          ld bc, eobanr-banner
          call 8252

; draw board
bdraw     ld de, board
          ld bc, eoboard-board
          call 8252
          ld hl, board+1
          ld a, (hl)
          inc a
          ld (hl), a
          cp 16 ; finish looping when lines 12 to 16 are drawn
          jr nz, bdraw

; draw player line
          ld de, player
          ld bc, eoplyr-player
          call 8252

; show player
ploop     ld hl, 22816
          ld bc, (ppos)
          add hl, bc
          ld a, (pcol)
          ld (hl), a

; invite player input
          ld hl, last_k
          ld a, (hl)
          cp 112
          jr z, pright
          cp 111
          jr z, pleft
          cp 32
          jr z, pfire
          cp 114
          jr z, newgame
          jr ploop

; restart game
newgame   ld hl, drop ; reset available drops for all 7 columns
          ld b, 7
rstdrp    ld (hl), 6 ; 6 means empty column (i.e. 6 drops remaining)
          inc hl ; move forward 1 byte within DROP until all 7 are reset
          djnz rstdrp
; clear board
          ld a, 6 ; A keeps track of rows
          ld b, 7 ; B keeps track of columns
          ld hl, 22860 ; addr 22860 is top-left attribute of board
          ld de, 25 ; 25 is the number of spaces from the end of one row to the beginning of the next
empty     ld (hl), 15 ; 15 is paper blue, ink white, i.e. an empty slot
          inc hl ; move forward one attribute
          djnz empty ; repeat until a row of seven slots is cleared
          ld b, 7 ; reset B in readiness for next row
          add hl, de ; skip to start of next row
          dec a ; subtract 1 from remaining rows
          cp 0 ; if all 6 rows are complete, end
          jp z, clrkey ; "
          jr empty ; if not, repeat

; player moves right
pright    ld a, (ppos)
          cp 18
          jr z, ploop
          ld hl, 22816
          ld bc, (ppos)
          add hl,bc
          ld (hl), 63
          ld a, (ppos)
          inc a
          ld (ppos), a
          jp clrkey

; player moves left
pleft     ld a, (ppos)
          cp 12
          jr z, ploop
          ld hl, 22816
          ld bc, (ppos)
          add hl, bc
          ld (hl), 63
          ld a, (ppos)
          dec a
          ld (ppos), a
          jp clrkey

; player fires
pfire     ld a, (ppos) ; get mathematical x position of player (i.e. x=12 is 1)
          sub 11 ; "
          ld hl, drop-1 ; point at mem loc prior to first column (because the loop incs)
          ld b, a ; use b to loop until correct column is reached
cntr      inc hl ; increase HL to scan across drop vars
          djnz cntr ; "
          ld a, (hl) ; load number of rows to descend into a
          ld (tdrop), a ; store A in TDROP (temporary drop)
          cp 0 ; if no spaces remain in column, jump back to player input loop
          jp z, clrkey ; "
          ld hl, 22816 ; erase player from screen
          ld bc, (ppos) ; "
          add hl, bc ; "
          ld (hl), 63 ; "

; counter drops
          ld a, (tdrop)
desnd     ld bc, 32 ; redraw player 1 row lower
          add hl, bc ; "
          ld d, a ; remember A temporarily in D
          ld a, (pcol+1)
          ld (hl), a ; "
          ld a, d ; put D back into A
          ld b, 5 ; create a brief delay between counter movements
stall     halt ; wait for an interrupt
          djnz stall ; loop
          ld (hl), 15 ; draw counter
          dec a ; A controls iterations of loop
          jr nz, desnd ; loop until descent finished
          ld a, (pcol+1) ; redraw counter in resting position
          ld (hl), a ; "

; decrement remaining slots by 1
          ld a, (ppos) ; get mathematical x position of player (i.e. x=12 is 1)
          sub 11 ; "
          ld hl, drop-1 ; point at mem loc prior to first column (because the loop incs)
          ld b, a ; use b to loop until correct column is reached
cntr2     inc hl ; increase HL to scan across drop vars
          djnz cntr2 ; "
          ld a, (tdrop) ; subtract one from slots remaining in selected column
          dec a ; "
          ld (tdrop), a ; "
          ld (hl), a ; "

; change colour for other player
          ld hl, ppos ; set player position back to centre
          ld (hl), 15 ; "
          ld a, (pcol) ; add 4 to colour (changing red to yellow), for above board
          add a, 4 ; "
          ld (pcol), a ; "
          ld a, (pcol+1) ; add 4 to colour (changing red to yellow), for within board
          add a, 4 ; "
          ld (pcol+1), a ; "
          cp 18 ; if colour is invalid, jump to BADCOL
          jr z, badcol ; "
          jr clrkey ; clear keyboard
badcol    ld a, 58 ; change invalid colour to red
          ld (pcol), a ; "
          ld a, 10 ; "
          ld (pcol+1), a ; "
          jr clrkey ; clear keyboard

; clear last keypress and loop back for new input
clrkey    ld hl, last_k
          ld (hl), 0
          jp ploop

; variables
ppos      defb 15, 0
pcol      defb 58, 10
drop      defb 6, 6, 6, 6, 6, 6, 6
tdrop     defb 0

banner    defb 22, 3, 11, "CONNECT 4"
eobanr    equ $

; board setup
board     defb 22, 10, 12
          defb 16, 7, 17, 1, 144, 144, 144, 144, 144, 144, 144
eoboard   equ $

player    defb 22, 9, 12
          defb 16, 7, 17, 7, 144, 144, 144, 144, 144, 144, 144
eoplyr    equ $

; graphics setup
udgs      defb 0, 24, 60, 126, 126, 60, 24, 0

end 50000