Game 1 Unit 13 of 64 1 hr learning time
AI Difficulty Levels
Choose your challenge: Easy (random), Medium (adjacent), or Hard (full strategy).
20% of Ink War
We’ve built three distinct AI behaviours across Units 9-12: random moves, adjacent priority, and full strategy with defense and position bonuses. But players can only face the hardest version. This unit lets them choose their challenge.
The title screen now offers four options. Two-player mode remains, but vs Computer splits into Easy, Medium, and Hard — each using a different AI algorithm.
Run It
pasmonext --sna inkwar.asm inkwar.sna
The new title screen shows all four options. Press 1-4 to select your game mode.
The Three Difficulties
Each difficulty level uses a different cell selection algorithm:
| Level | Algorithm | Behaviour |
|---|---|---|
| Easy | Random | Picks any empty cell at random. No strategy. |
| Medium | Adjacent priority | Expands from existing territory. No defense. |
| Hard | Full strategy | Offense + defense + position bonuses. |
Easy is beatable by anyone. Medium requires some thought. Hard plays optimally within its evaluation limits.
Difficulty Constants
We define the three levels as constants:
; AI difficulty levels
AI_EASY equ 0 ; Random moves
AI_MEDIUM equ 1 ; Adjacent priority only
AI_HARD equ 2 ; Full strategy (defense + position)
; Title screen positions - now four options
TITLE_ROW equ 6
TITLE_COL equ 12
MODE1_ROW equ 12 ; "1 - TWO PLAYER"
MODE1_COL equ 9
MODE2_ROW equ 14 ; "2 - AI EASY"
MODE2_COL equ 10
MODE3_ROW equ 16 ; "3 - AI MEDIUM"
MODE3_COL equ 9
MODE4_ROW equ 18 ; "4 - AI HARD"
MODE4_COL equ 10
The title screen repositions to accommodate four menu options instead of two.
Title Screen Selection
The keyboard reading now checks four keys instead of two:
state_title:
; Read keyboard row for keys 1-5
ld a, ROW_12345
in a, (KEY_PORT)
; Check for key 1 (Two Player)
bit 0, a ; Key 1
jr z, .st_two_player
; Check for key 2 (AI Easy)
bit 1, a ; Key 2
jr z, .st_ai_easy
; Check for key 3 (AI Medium)
bit 2, a ; Key 3
jr z, .st_ai_medium
; Check for key 4 (AI Hard)
bit 3, a ; Key 4
jr z, .st_ai_hard
jp main_loop ; No valid key - keep waiting
.st_two_player:
xor a ; GM_TWO_PLAYER = 0
ld (game_mode), a
call start_game
jp main_loop
.st_ai_easy:
ld a, GM_VS_AI
ld (game_mode), a
ld a, AI_EASY
ld (ai_difficulty), a
call start_game
jp main_loop
; .st_ai_medium and .st_ai_hard follow same pattern...
Keys 1-4 map to bits 0-3 of keyboard row $F7. Each AI option sets both game_mode (to GM_VS_AI) and ai_difficulty (to the appropriate level).
AI Dispatch
The core change is in ai_make_move, which now dispatches based on difficulty:
; ----------------------------------------------------------------------------
; AI Make Move
; ----------------------------------------------------------------------------
; AI picks a cell based on difficulty level
ai_make_move:
; Dispatch based on difficulty
ld a, (ai_difficulty)
or a
jr z, .aim_easy ; AI_EASY = 0
cp AI_MEDIUM
jr z, .aim_medium
; AI_HARD - full strategy
call find_best_adjacent_cell
jr .aim_have_cell
.aim_easy:
; Random moves
call find_random_empty_cell
jr .aim_have_cell
.aim_medium:
; Adjacent priority only (no defense/position)
call find_adjacent_only
.aim_have_cell:
; A = cell index (0-63), or $FF if board full
; ... rest of move handling ...
Three paths:
- Easy: Calls
find_random_empty_celldirectly - Medium: Calls new
find_adjacent_only(AI neighbours only) - Hard: Calls
find_best_adjacent_cell(full strategy)
Medium Difficulty Algorithm
Medium difficulty uses a simplified version of the scoring algorithm — only AI adjacency, no defense or position bonus:
find_adjacent_only:
; ... scan all cells ...
; For each empty cell:
call count_adjacent_ai ; Only this - no defense/position
; ... keep best score ...This creates an AI that expands its territory but doesn’t actively block you or prioritise strategic positions.
Why Three Distinct Algorithms?
We could have used probability-based mixing (e.g., Easy = 70% random, 30% strategic). But distinct algorithms are:
- Simpler to implement — No random number checks per move
- More predictable — Each level has consistent behaviour
- Easier to debug — Clear separation of concerns
- Better learning progression — Players see distinct AI personalities
The algorithms we built in Units 9-12 map naturally to difficulty levels.
The Complete Code
; ============================================================================
; INK WAR - Unit 13: AI Difficulty Levels
; ============================================================================
; Choose your challenge: Easy (random), Medium (adjacent), Hard (full strategy)
; Title screen now offers four options for different play styles.
;
; Controls: Q=Up, A=Down, O=Left, P=Right, SPACE=Claim
; 1=Two Player, 2=AI Easy, 3=AI Medium, 4=AI Hard
; ============================================================================
org 32768
; ----------------------------------------------------------------------------
; Constants
; ----------------------------------------------------------------------------
ATTR_BASE equ $5800
DISPLAY_FILE equ $4000
CHAR_SET equ $3C00 ; ROM character set base address
BOARD_ROW equ 8
BOARD_COL equ 12
BOARD_SIZE equ 8
; Display positions
SCORE_ROW equ 2 ; Score display row
P1_SCORE_COL equ 10 ; "P1: nn" column
P2_SCORE_COL equ 18 ; "P2: nn" column
TURN_ROW equ 4 ; Turn indicator row
TURN_COL equ 14 ; Turn indicator column
RESULT_ROW equ 20 ; Winner message row
RESULT_COL equ 11 ; Winner message column
; Game constants
TOTAL_CELLS equ 64 ; 8x8 board
; Customised colours (from Unit 3)
EMPTY_ATTR equ %01101000 ; Cyan paper + BRIGHT
BORDER_ATTR equ %01110000 ; Yellow paper + BRIGHT
CURSOR_ATTR equ %01111000 ; White paper + BRIGHT
P1_ATTR equ %01010000 ; Red paper + BRIGHT
P2_ATTR equ %01001000 ; Blue paper + BRIGHT
P1_CURSOR equ %01111010 ; White paper + Red ink + BRIGHT
P2_CURSOR equ %01111001 ; White paper + Blue ink + BRIGHT
; Text display attributes
TEXT_ATTR equ %00111000 ; White paper, black ink
P1_TEXT equ %01010111 ; Red paper, white ink + BRIGHT
P2_TEXT equ %01001111 ; Blue paper, white ink + BRIGHT
P1_BORDER equ 2
P2_BORDER equ 1
ERROR_BORDER equ 2 ; Red border for errors
; Keyboard ports
KEY_PORT equ $fe
ROW_QAOP equ $fb
ROW_ASDF equ $fd
ROW_YUIOP equ $df
ROW_SPACE equ $7f
; Cell states
STATE_EMPTY equ 0
STATE_P1 equ 1
STATE_P2 equ 2
; Game states (state machine)
GS_TITLE equ 0
GS_PLAYING equ 1
GS_RESULTS equ 2
; Game modes
GM_TWO_PLAYER equ 0
GM_VS_AI equ 1
; AI difficulty levels
AI_EASY equ 0 ; Random moves
AI_MEDIUM equ 1 ; Adjacent priority only
AI_HARD equ 2 ; Full strategy (defense + position)
; AI timing
AI_DELAY equ 25 ; Frames before AI moves (~0.5 sec)
; Title screen positions
TITLE_ROW equ 6
TITLE_COL equ 12 ; "INK WAR" (7 chars) centred
MODE1_ROW equ 12 ; "1 - TWO PLAYER"
MODE1_COL equ 9
MODE2_ROW equ 14 ; "2 - AI EASY"
MODE2_COL equ 10
MODE3_ROW equ 16 ; "3 - AI MEDIUM"
MODE3_COL equ 9
MODE4_ROW equ 18 ; "4 - AI HARD"
MODE4_COL equ 10
; Results screen positions
CONTINUE_ROW equ 22 ; "PRESS ANY KEY" after results
CONTINUE_COL equ 9 ; (32-13)/2 = 9.5
; Input timing
KEY_DELAY equ 8 ; Frames between key repeats
; ----------------------------------------------------------------------------
; Entry Point
; ----------------------------------------------------------------------------
start:
; Start at title screen
ld a, GS_TITLE
ld (game_state), a
call init_screen
call draw_title_screen
; Black border for title
xor a
out (KEY_PORT), a
main_loop:
halt
; Dispatch based on game state
ld a, (game_state)
or a
jr z, state_title ; GS_TITLE = 0
cp GS_PLAYING
jr z, state_playing
; Must be GS_RESULTS - handled inline after game over
jp main_loop
; ----------------------------------------------------------------------------
; State: Title
; ----------------------------------------------------------------------------
; Waits for 1 (Two Player), 2 (AI Easy), 3 (AI Medium), 4 (AI Hard)
ROW_12345 equ $f7 ; Keyboard row for 1,2,3,4,5
state_title:
; Read keyboard row for keys 1-5
ld a, ROW_12345
in a, (KEY_PORT)
; Check for key 1 (Two Player)
bit 0, a ; Key 1
jr z, .st_two_player
; Check for key 2 (AI Easy)
bit 1, a ; Key 2
jr z, .st_ai_easy
; Check for key 3 (AI Medium)
bit 2, a ; Key 3
jr z, .st_ai_medium
; Check for key 4 (AI Hard)
bit 3, a ; Key 4
jr z, .st_ai_hard
jp main_loop ; No valid key - keep waiting
.st_two_player:
xor a ; GM_TWO_PLAYER = 0
ld (game_mode), a
call start_game
jp main_loop
.st_ai_easy:
ld a, GM_VS_AI
ld (game_mode), a
ld a, AI_EASY
ld (ai_difficulty), a
call start_game
jp main_loop
.st_ai_medium:
ld a, GM_VS_AI
ld (game_mode), a
ld a, AI_MEDIUM
ld (ai_difficulty), a
call start_game
jp main_loop
.st_ai_hard:
ld a, GM_VS_AI
ld (game_mode), a
ld a, AI_HARD
ld (ai_difficulty), a
call start_game
jp main_loop
; ----------------------------------------------------------------------------
; State: Playing
; ----------------------------------------------------------------------------
state_playing:
; Check if AI's turn (Player 2 in vs AI mode)
ld a, (game_mode)
or a
jr z, .sp_human ; Two player mode - human controls
; vs AI mode - check if Player 2's turn
ld a, (current_player)
cp 2
jr z, .sp_ai_turn
.sp_human:
; Human player's turn
call read_keyboard
call handle_input
jp main_loop
.sp_ai_turn:
; AI's turn - use delay counter
ld a, (ai_timer)
or a
jr z, .sp_ai_move ; Timer expired, make move
; Still waiting
dec a
ld (ai_timer), a
jp main_loop
.sp_ai_move:
; Reset timer for next AI turn
ld a, AI_DELAY
ld (ai_timer), a
; AI makes a move
call ai_make_move
jp main_loop
; ----------------------------------------------------------------------------
; Start Game
; ----------------------------------------------------------------------------
; Transitions from title to playing state
start_game:
ld a, GS_PLAYING
ld (game_state), a
call init_screen
call init_game
call draw_board_border
call draw_board
call draw_ui
call draw_cursor
call update_border
; Wait for key release before playing
call wait_key_release
ret
; ----------------------------------------------------------------------------
; Initialise Screen
; ----------------------------------------------------------------------------
init_screen:
xor a
out (KEY_PORT), a
; Clear display file (pixels)
ld hl, DISPLAY_FILE
ld de, DISPLAY_FILE+1
ld bc, 6143
ld (hl), 0
ldir
; Clear all attributes to white paper, black ink
ld hl, ATTR_BASE
ld de, ATTR_BASE+1
ld bc, 767
ld (hl), TEXT_ATTR ; White background for text areas
ldir
ret
; ----------------------------------------------------------------------------
; Draw UI
; ----------------------------------------------------------------------------
; Draws score display and turn indicator
draw_ui:
call draw_scores
call draw_turn_indicator
ret
; ----------------------------------------------------------------------------
; Draw Scores
; ----------------------------------------------------------------------------
; Displays "P1: nn P2: nn" with player colours
draw_scores:
; Count cells for each player
call count_cells
; Draw P1 label "P1:"
ld b, SCORE_ROW
ld c, P1_SCORE_COL
ld a, 'P'
call print_char
inc c
ld a, '1'
call print_char
inc c
ld a, ':'
call print_char
inc c
; Print P1 score
ld a, (p1_count)
call print_two_digits
; Set P1 colour attribute
ld a, SCORE_ROW
ld c, P1_SCORE_COL
ld b, 5 ; "P1:nn" = 5 characters
ld e, P1_TEXT
call set_attr_range
; Draw P2 label "P2:"
ld b, SCORE_ROW
ld c, P2_SCORE_COL
ld a, 'P'
call print_char
inc c
ld a, '2'
call print_char
inc c
ld a, ':'
call print_char
inc c
; Print P2 score
ld a, (p2_count)
call print_two_digits
; Set P2 colour attribute
ld a, SCORE_ROW
ld c, P2_SCORE_COL
ld b, 5
ld e, P2_TEXT
call set_attr_range
ret
; ----------------------------------------------------------------------------
; Draw Turn Indicator
; ----------------------------------------------------------------------------
; Shows "TURN" with current player's colour
draw_turn_indicator:
; Print "TURN"
ld b, TURN_ROW
ld c, TURN_COL
ld a, 'T'
call print_char
inc c
ld a, 'U'
call print_char
inc c
ld a, 'R'
call print_char
inc c
ld a, 'N'
call print_char
; Set attribute based on current player
ld a, (current_player)
cp 1
jr z, .dti_p1
ld e, P2_TEXT
jr .dti_set
.dti_p1:
ld e, P1_TEXT
.dti_set:
ld a, TURN_ROW
ld c, TURN_COL
ld b, 4 ; "TURN" = 4 chars
call set_attr_range
ret
; ----------------------------------------------------------------------------
; Print Character
; ----------------------------------------------------------------------------
; A = ASCII character (32-127), B = row (0-23), C = column (0-31)
; Writes character directly to display file using ROM character set
print_char:
push bc
push de
push hl
push af
; Calculate character data address: CHAR_SET + char*8
ld l, a
ld h, 0
add hl, hl
add hl, hl
add hl, hl ; HL = char * 8
ld de, CHAR_SET
add hl, de ; HL = source address
push hl ; Save character data address
; Calculate display file address
; Screen address: high byte varies with row, low byte = column
ld a, b ; A = row (0-23)
and %00011000 ; Get which third (0, 8, 16)
add a, $40 ; Add display file base high byte
ld d, a
ld a, b ; A = row
and %00000111 ; Get line within character row
rrca
rrca
rrca ; Shift to bits 5-7
add a, c ; Add column
ld e, a ; DE = screen address
pop hl ; HL = character data
; Copy 8 bytes (8 pixel rows of character)
ld b, 8
.pc_loop:
ld a, (hl)
ld (de), a
inc hl
inc d ; Next screen line (add 256)
djnz .pc_loop
pop af
pop hl
pop de
pop bc
ret
; ----------------------------------------------------------------------------
; Print Two Digits
; ----------------------------------------------------------------------------
; A = number (0-99), B = row, C = column (will advance by 2)
; Prints number as two digits
print_two_digits:
push bc
; Calculate tens digit
ld d, 0 ; Tens counter
.ptd_tens:
cp 10
jr c, .ptd_print
sub 10
inc d
jr .ptd_tens
.ptd_print:
push af ; Save units digit
; Print tens digit
ld a, d
add a, '0'
call print_char
inc c
; Print units digit
pop af
add a, '0'
call print_char
inc c
pop bc
ret
; ----------------------------------------------------------------------------
; Count Cells
; ----------------------------------------------------------------------------
; Counts cells owned by each player
count_cells:
xor a
ld (p1_count), a
ld (p2_count), a
ld hl, board_state
ld b, 64 ; 64 cells
.cc_loop:
ld a, (hl)
cp STATE_P1
jr nz, .cc_not_p1
ld a, (p1_count)
inc a
ld (p1_count), a
jr .cc_next
.cc_not_p1:
cp STATE_P2
jr nz, .cc_next
ld a, (p2_count)
inc a
ld (p2_count), a
.cc_next:
inc hl
djnz .cc_loop
ret
; ----------------------------------------------------------------------------
; Set Attribute Range
; ----------------------------------------------------------------------------
; A = row, C = start column, B = count, E = attribute
set_attr_range:
push bc
push de
; Calculate start address: ATTR_BASE + row*32 + col
ld l, a
ld h, 0
add hl, hl
add hl, hl
add hl, hl
add hl, hl
add hl, hl ; HL = row * 32
ld a, c
add a, l
ld l, a
ld bc, ATTR_BASE
add hl, bc ; HL = attribute address
pop de ; E = attribute
pop bc ; B = count
.sar_loop:
ld (hl), e
inc hl
djnz .sar_loop
ret
; ----------------------------------------------------------------------------
; Update Border
; ----------------------------------------------------------------------------
update_border:
ld a, (current_player)
cp 1
jr z, .ub_p1
ld a, P2_BORDER
jr .ub_set
.ub_p1:
ld a, P1_BORDER
.ub_set:
out (KEY_PORT), a
ret
; ----------------------------------------------------------------------------
; Initialise Game State
; ----------------------------------------------------------------------------
init_game:
ld hl, board_state
ld b, 64
xor a
.ig_loop:
ld (hl), a
inc hl
djnz .ig_loop
ld a, 1
ld (current_player), a
xor a
ld (cursor_row), a
ld (cursor_col), a
ld (p1_count), a
ld (p2_count), a
ld (last_key), a ; No previous key
ld (key_timer), a ; No delay active
; Initialize AI timer
ld a, AI_DELAY
ld (ai_timer), a
ret
; ----------------------------------------------------------------------------
; Draw Board Border
; ----------------------------------------------------------------------------
draw_board_border:
ld c, BOARD_ROW-1
ld d, BOARD_COL-1
ld b, BOARD_SIZE+2
call draw_border_row
ld c, BOARD_ROW+BOARD_SIZE
ld d, BOARD_COL-1
ld b, BOARD_SIZE+2
call draw_border_row
ld c, BOARD_ROW
ld d, BOARD_COL-1
ld b, BOARD_SIZE
call draw_border_col
ld c, BOARD_ROW
ld d, BOARD_COL+BOARD_SIZE
ld b, BOARD_SIZE
call draw_border_col
ret
draw_border_row:
push bc
.dbr_loop:
push bc
push de
ld a, c
ld l, a
ld h, 0
add hl, hl
add hl, hl
add hl, hl
add hl, hl
add hl, hl
ld a, d
add a, l
ld l, a
ld bc, ATTR_BASE
add hl, bc
ld (hl), BORDER_ATTR
pop de
pop bc
inc d
djnz .dbr_loop
pop bc
ret
draw_border_col:
push bc
.dbc_loop:
push bc
push de
ld a, c
ld l, a
ld h, 0
add hl, hl
add hl, hl
add hl, hl
add hl, hl
add hl, hl
ld a, d
add a, l
ld l, a
ld bc, ATTR_BASE
add hl, bc
ld (hl), BORDER_ATTR
pop de
pop bc
inc c
djnz .dbc_loop
pop bc
ret
; ----------------------------------------------------------------------------
; Draw Board
; ----------------------------------------------------------------------------
draw_board:
ld b, BOARD_SIZE
ld c, BOARD_ROW
.db_row:
push bc
ld b, BOARD_SIZE
ld d, BOARD_COL
.db_col:
push bc
ld a, c
ld l, a
ld h, 0
add hl, hl
add hl, hl
add hl, hl
add hl, hl
add hl, hl
ld a, d
add a, l
ld l, a
ld bc, ATTR_BASE
add hl, bc
ld (hl), EMPTY_ATTR
pop bc
inc d
djnz .db_col
pop bc
inc c
djnz .db_row
ret
; ----------------------------------------------------------------------------
; Draw Cursor
; ----------------------------------------------------------------------------
draw_cursor:
call get_cell_state
cp STATE_P1
jr z, .dc_p1
cp STATE_P2
jr z, .dc_p2
ld a, CURSOR_ATTR
jr .dc_set
.dc_p1:
ld a, P1_CURSOR
jr .dc_set
.dc_p2:
ld a, P2_CURSOR
.dc_set:
push af
ld a, (cursor_row)
add a, BOARD_ROW
ld l, a
ld h, 0
add hl, hl
add hl, hl
add hl, hl
add hl, hl
add hl, hl
ld a, (cursor_col)
add a, BOARD_COL
add a, l
ld l, a
ld bc, ATTR_BASE
add hl, bc
pop af
ld (hl), a
ret
; ----------------------------------------------------------------------------
; Clear Cursor
; ----------------------------------------------------------------------------
clear_cursor:
call get_cell_state
cp STATE_P1
jr z, .clc_p1
cp STATE_P2
jr z, .clc_p2
ld a, EMPTY_ATTR
jr .clc_set
.clc_p1:
ld a, P1_ATTR
jr .clc_set
.clc_p2:
ld a, P2_ATTR
.clc_set:
push af
ld a, (cursor_row)
add a, BOARD_ROW
ld l, a
ld h, 0
add hl, hl
add hl, hl
add hl, hl
add hl, hl
add hl, hl
ld a, (cursor_col)
add a, BOARD_COL
add a, l
ld l, a
ld bc, ATTR_BASE
add hl, bc
pop af
ld (hl), a
ret
; ----------------------------------------------------------------------------
; Get Cell State
; ----------------------------------------------------------------------------
get_cell_state:
ld a, (cursor_row)
add a, a
add a, a
add a, a
ld hl, board_state
ld b, 0
ld c, a
add hl, bc
ld a, (cursor_col)
ld c, a
add hl, bc
ld a, (hl)
ret
; ----------------------------------------------------------------------------
; Read Keyboard
; ----------------------------------------------------------------------------
read_keyboard:
xor a
ld (key_pressed), a
ld a, ROW_QAOP
in a, (KEY_PORT)
bit 0, a
jr nz, .rk_not_q
ld a, 1
ld (key_pressed), a
ret
.rk_not_q:
ld a, ROW_ASDF
in a, (KEY_PORT)
bit 0, a
jr nz, .rk_not_a
ld a, 2
ld (key_pressed), a
ret
.rk_not_a:
ld a, ROW_YUIOP
in a, (KEY_PORT)
bit 1, a
jr nz, .rk_not_o
ld a, 3
ld (key_pressed), a
ret
.rk_not_o:
ld a, ROW_YUIOP
in a, (KEY_PORT)
bit 0, a
jr nz, .rk_not_p
ld a, 4
ld (key_pressed), a
ret
.rk_not_p:
ld a, ROW_SPACE
in a, (KEY_PORT)
bit 0, a
jr nz, .rk_not_space
ld a, 5
ld (key_pressed), a
.rk_not_space:
ret
; ----------------------------------------------------------------------------
; Handle Input
; ----------------------------------------------------------------------------
; Implements key repeat delay for smooth cursor movement
handle_input:
ld a, (key_pressed)
or a
jr nz, .hi_have_key
; No key pressed - reset tracking
xor a
ld (last_key), a
ld (key_timer), a
ret
.hi_have_key:
; Space (claim) always works immediately
cp 5
jr z, try_claim
; Check if same key as last frame
ld b, a ; Save current key
ld a, (last_key)
cp b
jr nz, .hi_new_key
; Same key - check timer
ld a, (key_timer)
or a
jr z, .hi_allow ; Timer expired, allow repeat
dec a
ld (key_timer), a
ret ; Still waiting
.hi_new_key:
; New key pressed - save it and reset timer
ld a, b
ld (last_key), a
ld a, KEY_DELAY
ld (key_timer), a
.hi_allow:
; Process movement
call clear_cursor
ld a, (key_pressed)
cp 1
jr nz, .hi_not_up
ld a, (cursor_row)
or a
jr z, .hi_done
dec a
ld (cursor_row), a
jr .hi_done
.hi_not_up:
cp 2
jr nz, .hi_not_down
ld a, (cursor_row)
cp BOARD_SIZE-1
jr z, .hi_done
inc a
ld (cursor_row), a
jr .hi_done
.hi_not_down:
cp 3
jr nz, .hi_not_left
ld a, (cursor_col)
or a
jr z, .hi_done
dec a
ld (cursor_col), a
jr .hi_done
.hi_not_left:
cp 4
jr nz, .hi_done
ld a, (cursor_col)
cp BOARD_SIZE-1
jr z, .hi_done
inc a
ld (cursor_col), a
.hi_done:
call draw_cursor
ret
; ----------------------------------------------------------------------------
; Try Claim Cell
; ----------------------------------------------------------------------------
try_claim:
call get_cell_state
or a
jr z, .tc_valid
; Cell already claimed - error feedback
call sound_error
call flash_border_error
call update_border ; Restore correct border colour
ret
.tc_valid:
; Valid move - claim the cell
call claim_cell
call sound_claim
ld a, (current_player)
xor 3
ld (current_player), a
call draw_ui ; Update scores and turn indicator
; Check if game is over
call check_game_over
or a
jr z, .tc_continue
; Game over - show results and return to title
call show_results
call victory_celebration
call wait_for_key
; Return to title screen
ld a, GS_TITLE
ld (game_state), a
call init_screen
call draw_title_screen
xor a
out (KEY_PORT), a ; Black border for title
ret
.tc_continue:
call update_border
call draw_cursor
ret
; ----------------------------------------------------------------------------
; Claim Cell
; ----------------------------------------------------------------------------
claim_cell:
ld a, (cursor_row)
add a, a
add a, a
add a, a
ld hl, board_state
ld b, 0
ld c, a
add hl, bc
ld a, (cursor_col)
ld c, a
add hl, bc
ld a, (current_player)
ld (hl), a
push af
ld a, (cursor_row)
add a, BOARD_ROW
ld l, a
ld h, 0
add hl, hl
add hl, hl
add hl, hl
add hl, hl
add hl, hl
ld a, (cursor_col)
add a, BOARD_COL
add a, l
ld l, a
ld bc, ATTR_BASE
add hl, bc
pop af
cp 1
jr z, .clm_is_p1
ld (hl), P2_ATTR
ret
.clm_is_p1:
ld (hl), P1_ATTR
ret
; ----------------------------------------------------------------------------
; Sound - Claim
; ----------------------------------------------------------------------------
sound_claim:
ld hl, 400
ld b, 20
.scl_loop:
push bc
push hl
ld b, h
ld c, l
.scl_tone:
ld a, $10
out (KEY_PORT), a
call .scl_delay
xor a
out (KEY_PORT), a
call .scl_delay
dec bc
ld a, b
or c
jr nz, .scl_tone
pop hl
pop bc
ld de, 20
or a
sbc hl, de
djnz .scl_loop
ret
.scl_delay:
push bc
ld b, 5
.scl_delay_loop:
djnz .scl_delay_loop
pop bc
ret
; ----------------------------------------------------------------------------
; Sound - Error
; ----------------------------------------------------------------------------
; Harsh buzz for invalid move
sound_error:
ld b, 30 ; Duration
.se_loop:
push bc
; Low frequency buzz (longer delay = lower pitch)
ld a, $10
out (KEY_PORT), a
ld c, 80 ; Longer delay for low pitch
.se_delay1:
dec c
jr nz, .se_delay1
xor a
out (KEY_PORT), a
ld c, 80
.se_delay2:
dec c
jr nz, .se_delay2
pop bc
djnz .se_loop
ret
; ----------------------------------------------------------------------------
; Flash Border Error
; ----------------------------------------------------------------------------
; Flash border red briefly to indicate error
flash_border_error:
; Flash red 3 times
ld b, 3
.fbe_loop:
push bc
; Red border
ld a, ERROR_BORDER
out (KEY_PORT), a
; Short delay (about 3 frames)
ld bc, 8000
.fbe_delay1:
dec bc
ld a, b
or c
jr nz, .fbe_delay1
; Black border (brief off)
xor a
out (KEY_PORT), a
; Short delay
ld bc, 4000
.fbe_delay2:
dec bc
ld a, b
or c
jr nz, .fbe_delay2
pop bc
djnz .fbe_loop
ret
; ----------------------------------------------------------------------------
; Check Game Over
; ----------------------------------------------------------------------------
; Returns A=1 if game is over (board full), A=0 otherwise
check_game_over:
; Game is over when p1_count + p2_count == 64
ld a, (p1_count)
ld b, a
ld a, (p2_count)
add a, b
cp TOTAL_CELLS
jr z, .cgo_over
xor a ; Not over
ret
.cgo_over:
ld a, 1 ; Game over
ret
; ----------------------------------------------------------------------------
; Show Results
; ----------------------------------------------------------------------------
; Displays winner message based on scores
show_results:
; Clear turn indicator
ld a, TURN_ROW
ld c, TURN_COL
ld b, 4
ld e, TEXT_ATTR
call set_attr_range
; Determine winner
ld a, (p1_count)
ld b, a
ld a, (p2_count)
cp b
jr c, .sr_p1_wins ; p2 < p1, so p1 wins
jr z, .sr_draw ; p1 == p2, draw
; p2 > p1, p2 wins
jr .sr_p2_wins
.sr_p1_wins:
; Display "P1 WINS!"
ld b, RESULT_ROW
ld c, RESULT_COL
ld hl, msg_p1_wins
ld e, P1_TEXT
call print_message
jr .sr_continue
.sr_p2_wins:
; Display "P2 WINS!"
ld b, RESULT_ROW
ld c, RESULT_COL
ld hl, msg_p2_wins
ld e, P2_TEXT
call print_message
jr .sr_continue
.sr_draw:
; Display "DRAW!"
ld b, RESULT_ROW
ld c, RESULT_COL + 2 ; Centre "DRAW!" better
ld hl, msg_draw
ld e, TEXT_ATTR
call print_message
.sr_continue:
; Display "PRESS ANY KEY" prompt
ld b, CONTINUE_ROW
ld c, CONTINUE_COL
ld hl, msg_continue
ld e, TEXT_ATTR
call print_message
ret
; ----------------------------------------------------------------------------
; Print Message
; ----------------------------------------------------------------------------
; HL = pointer to null-terminated string
; B = row, C = starting column, E = attribute for message area
print_message:
; Save parameters we need later
push de ; Save attribute in E
push bc ; Save row (B) and start column (C)
; Print characters
.pm_loop:
ld a, (hl)
or a
jr z, .pm_done
call print_char
inc hl
inc c
jr .pm_loop
.pm_done:
; C now has end column
; Calculate length: end_col - start_col
ld a, c ; A = end column
pop bc ; B = row, C = start column
sub c ; A = length
ld d, a ; D = length (save it)
; Set up for set_attr_range: A=row, C=start_col, B=count, E=attr
ld a, b ; A = row
ld b, d ; B = count (length)
pop de ; E = attribute
call set_attr_range
ret
; ----------------------------------------------------------------------------
; Victory Celebration
; ----------------------------------------------------------------------------
; Flashes border in winner's colour
victory_celebration:
; Determine winner's border colour
ld a, (p1_count)
ld b, a
ld a, (p2_count)
cp b
jr c, .vc_p1 ; p2 < p1
jr z, .vc_draw ; draw - use white
ld d, P2_BORDER ; p2 wins
jr .vc_flash
.vc_p1:
ld d, P1_BORDER
jr .vc_flash
.vc_draw:
ld d, 7 ; White for draw
.vc_flash:
; Flash border 5 times
ld b, 5
.vc_loop:
push bc
; Winner's colour
ld a, d
out (KEY_PORT), a
; Delay
ld bc, 15000
.vc_delay1:
dec bc
ld a, b
or c
jr nz, .vc_delay1
; Black
xor a
out (KEY_PORT), a
; Delay
ld bc, 10000
.vc_delay2:
dec bc
ld a, b
or c
jr nz, .vc_delay2
pop bc
djnz .vc_loop
ret
; ----------------------------------------------------------------------------
; Draw Title Screen
; ----------------------------------------------------------------------------
; Displays game title and prompt
draw_title_screen:
; Draw "INK WAR" title
ld b, TITLE_ROW
ld c, TITLE_COL
ld hl, msg_title
ld e, TEXT_ATTR
call print_message
; Draw "1 - TWO PLAYER"
ld b, MODE1_ROW
ld c, MODE1_COL
ld hl, msg_mode1
ld e, TEXT_ATTR
call print_message
; Draw "2 - AI EASY"
ld b, MODE2_ROW
ld c, MODE2_COL
ld hl, msg_mode2
ld e, TEXT_ATTR
call print_message
; Draw "3 - AI MEDIUM"
ld b, MODE3_ROW
ld c, MODE3_COL
ld hl, msg_mode3
ld e, TEXT_ATTR
call print_message
; Draw "4 - AI HARD"
ld b, MODE4_ROW
ld c, MODE4_COL
ld hl, msg_mode4
ld e, TEXT_ATTR
call print_message
ret
; ----------------------------------------------------------------------------
; Wait Key Release
; ----------------------------------------------------------------------------
; Waits until all keys are released
wait_key_release:
.wkr_loop:
xor a
in a, (KEY_PORT)
cpl ; Invert (keys are active low)
and %00011111 ; Mask to key bits
jr nz, .wkr_loop ; Still holding a key
ret
; ----------------------------------------------------------------------------
; Wait For Key
; ----------------------------------------------------------------------------
; Waits until any key is pressed
wait_for_key:
; First wait for all keys to be released
.wfk_release:
xor a
in a, (KEY_PORT)
cpl ; Invert (keys are active low)
and %00011111 ; Mask to key bits
jr nz, .wfk_release
; Now wait for a key press
.wfk_wait:
halt ; Wait for interrupt
xor a
in a, (KEY_PORT)
cpl
and %00011111
jr z, .wfk_wait
ret
; ----------------------------------------------------------------------------
; AI Make Move
; ----------------------------------------------------------------------------
; AI picks a cell based on difficulty level
ai_make_move:
; Dispatch based on difficulty
ld a, (ai_difficulty)
or a
jr z, .aim_easy ; AI_EASY = 0
cp AI_MEDIUM
jr z, .aim_medium
; AI_HARD - full strategy
call find_best_adjacent_cell
jr .aim_have_cell
.aim_easy:
; Random moves
call find_random_empty_cell
jr .aim_have_cell
.aim_medium:
; Adjacent priority only (no defense/position)
call find_adjacent_only
; Fall through to .aim_have_cell
.aim_have_cell:
; A = cell index (0-63), or $FF if board full
cp $ff
ret z ; No empty cells (shouldn't happen)
; Convert index to row/col and set cursor
ld b, a
and %00000111 ; Column = index AND 7
ld (cursor_col), a
ld a, b
rrca
rrca
rrca
and %00000111 ; Row = index >> 3
ld (cursor_row), a
; Claim the cell (reuse existing code)
call claim_cell
call sound_claim
; Switch player
ld a, (current_player)
xor 3
ld (current_player), a
call draw_ui
; Check if game is over
call check_game_over
or a
jr z, .aim_continue
; Game over - show results and return to title
call show_results
call victory_celebration
call wait_for_key
; Return to title screen
ld a, GS_TITLE
ld (game_state), a
call init_screen
call draw_title_screen
xor a
out (KEY_PORT), a ; Black border for title
ret
.aim_continue:
call update_border
call draw_cursor
ret
; ----------------------------------------------------------------------------
; Find Best Cell (Offense + Defense + Position)
; ----------------------------------------------------------------------------
; Returns A = index of empty cell with best combined score, or $FF if none
; Score = adjacent AI + adjacent human + position bonus (corner=2, edge=1)
; This makes the AI value strategic positions in addition to adjacency
find_best_adjacent_cell:
; Initialize best tracking
ld a, $ff
ld (best_cell), a ; No best cell yet
xor a
ld (best_score), a ; Best score = 0
; Scan all 64 cells
ld c, 0 ; C = current cell index
.fbac_loop:
; Check if cell is empty
ld hl, board_state
ld d, 0
ld e, c
add hl, de
ld a, (hl)
or a
jr nz, .fbac_next ; Not empty, skip
; Empty cell - count adjacent AI cells (offense)
push bc
ld a, c
call count_adjacent_ai
ld b, a ; B = AI adjacent count
; Count adjacent human cells (defense)
ld a, c
call count_adjacent_p1
add a, b ; A = adjacency score
ld b, a ; B = adjacency score
; Add position bonus (corners=2, edges=1)
ld a, c
call get_position_bonus
add a, b ; A = total score
pop bc
; Compare with best score
ld b, a ; B = this score
ld a, (best_score)
cp b
jr nc, .fbac_next ; Current best >= this score
; New best found
ld a, b
ld (best_score), a
ld a, c
ld (best_cell), a
.fbac_next:
inc c
ld a, c
cp 64
jr c, .fbac_loop ; Continue if c < 64
; Check if we found a good cell
ld a, (best_score)
or a
jr z, .fbac_random ; No scored cells, use random
; Return best cell
ld a, (best_cell)
ret
.fbac_random:
; Fall back to random empty cell
call find_random_empty_cell
ret
best_cell: defb 0
best_score: defb 0
; ----------------------------------------------------------------------------
; Find Adjacent Only (Medium Difficulty)
; ----------------------------------------------------------------------------
; Returns A = index of empty cell with most AI neighbors, or $FF if none
; Only considers AI adjacency - no defense or position bonus
find_adjacent_only:
; Initialize best tracking
ld a, $ff
ld (best_cell), a
xor a
ld (best_score), a
; Scan all 64 cells
ld c, 0
.fao_loop:
; Check if cell is empty
ld hl, board_state
ld d, 0
ld e, c
add hl, de
ld a, (hl)
or a
jr nz, .fao_next
; Empty cell - count adjacent AI cells only
push bc
ld a, c
call count_adjacent_ai
pop bc
; Compare with best score
ld b, a
ld a, (best_score)
cp b
jr nc, .fao_next
; New best found
ld a, b
ld (best_score), a
ld a, c
ld (best_cell), a
.fao_next:
inc c
ld a, c
cp 64
jr c, .fao_loop
; Check if we found an adjacent cell
ld a, (best_score)
or a
jr z, .fao_random
; Return best adjacent cell
ld a, (best_cell)
ret
.fao_random:
; Fall back to random empty cell
call find_random_empty_cell
ret
; ----------------------------------------------------------------------------
; Get Position Bonus
; ----------------------------------------------------------------------------
; A = cell index (0-63)
; Returns A = position bonus (corner=2, edge=1, center=0)
get_position_bonus:
; Get row and column from index
ld b, a
and %00000111 ; Column (0-7)
ld c, a
ld a, b
rrca
rrca
rrca
and %00000111 ; Row (0-7)
ld b, a ; B = row, C = col
; Check for corner (row=0 or 7, col=0 or 7)
ld a, b
or a
jr z, .gpb_row_edge ; Row 0
cp 7
jr z, .gpb_row_edge ; Row 7
; Row is not edge
ld a, c
or a
jr z, .gpb_edge ; Col 0, row not edge = edge
cp 7
jr z, .gpb_edge ; Col 7, row not edge = edge
; Neither row nor col is edge = center
xor a ; Return 0
ret
.gpb_row_edge:
; Row is 0 or 7, check column
ld a, c
or a
jr z, .gpb_corner ; Col 0 = corner
cp 7
jr z, .gpb_corner ; Col 7 = corner
; Row edge but not corner
jr .gpb_edge
.gpb_corner:
ld a, 2 ; Corner bonus
ret
.gpb_edge:
ld a, 1 ; Edge bonus
ret
; ----------------------------------------------------------------------------
; Count Adjacent AI Cells
; ----------------------------------------------------------------------------
; A = cell index (0-63)
; Returns A = count of adjacent cells owned by AI (P2)
count_adjacent_ai:
ld (temp_cell), a
xor a
ld (adj_count), a
; Get row and column
ld a, (temp_cell)
ld b, a
and %00000111 ; Column
ld c, a
ld a, b
rrca
rrca
rrca
and %00000111 ; Row
ld b, a ; B = row, C = col
; Check up (row-1)
ld a, b
or a
jr z, .caa_skip_up ; Row 0, no up neighbor
dec a ; Row - 1
push bc
ld b, a
call .caa_check_cell
pop bc
.caa_skip_up:
; Check down (row+1)
ld a, b
cp 7
jr z, .caa_skip_down ; Row 7, no down neighbor
inc a ; Row + 1
push bc
ld b, a
call .caa_check_cell
pop bc
.caa_skip_down:
; Check left (col-1)
ld a, c
or a
jr z, .caa_skip_left ; Col 0, no left neighbor
dec a ; Col - 1
push bc
ld c, a
call .caa_check_cell
pop bc
.caa_skip_left:
; Check right (col+1)
ld a, c
cp 7
jr z, .caa_skip_right ; Col 7, no right neighbor
inc a ; Col + 1
push bc
ld c, a
call .caa_check_cell
pop bc
.caa_skip_right:
ld a, (adj_count)
ret
; Helper: check if cell at (B,C) is AI owned
.caa_check_cell:
; Calculate index: row*8 + col
ld a, b
rlca
rlca
rlca ; Row * 8
add a, c ; + col
ld hl, board_state
ld d, 0
ld e, a
add hl, de
ld a, (hl)
cp STATE_P2 ; AI is Player 2
ret nz ; Not AI cell
; AI cell - increment count
ld a, (adj_count)
inc a
ld (adj_count), a
ret
temp_cell: defb 0
adj_count: defb 0
; ----------------------------------------------------------------------------
; Count Adjacent Human Cells
; ----------------------------------------------------------------------------
; A = cell index (0-63)
; Returns A = count of adjacent cells owned by human (P1)
count_adjacent_p1:
ld (temp_cell), a
xor a
ld (adj_count), a
; Get row and column
ld a, (temp_cell)
ld b, a
and %00000111 ; Column
ld c, a
ld a, b
rrca
rrca
rrca
and %00000111 ; Row
ld b, a ; B = row, C = col
; Check up (row-1)
ld a, b
or a
jr z, .cap_skip_up ; Row 0, no up neighbor
dec a ; Row - 1
push bc
ld b, a
call .cap_check_cell
pop bc
.cap_skip_up:
; Check down (row+1)
ld a, b
cp 7
jr z, .cap_skip_down ; Row 7, no down neighbor
inc a ; Row + 1
push bc
ld b, a
call .cap_check_cell
pop bc
.cap_skip_down:
; Check left (col-1)
ld a, c
or a
jr z, .cap_skip_left ; Col 0, no left neighbor
dec a ; Col - 1
push bc
ld c, a
call .cap_check_cell
pop bc
.cap_skip_left:
; Check right (col+1)
ld a, c
cp 7
jr z, .cap_skip_right ; Col 7, no right neighbor
inc a ; Col + 1
push bc
ld c, a
call .cap_check_cell
pop bc
.cap_skip_right:
ld a, (adj_count)
ret
; Helper: check if cell at (B,C) is human owned
.cap_check_cell:
; Calculate index: row*8 + col
ld a, b
rlca
rlca
rlca ; Row * 8
add a, c ; + col
ld hl, board_state
ld d, 0
ld e, a
add hl, de
ld a, (hl)
cp STATE_P1 ; Human is Player 1
ret nz ; Not human cell
; Human cell - increment count
ld a, (adj_count)
inc a
ld (adj_count), a
ret
; ----------------------------------------------------------------------------
; Find Random Empty Cell
; ----------------------------------------------------------------------------
; Returns A = index of a random empty cell (0-63), or $FF if none
find_random_empty_cell:
; Get random starting position
call get_random
and %00111111 ; Limit to 0-63
ld c, a ; C = start index
ld b, 64 ; B = cells to check
.frec_loop:
; Check if cell at index C is empty
ld hl, board_state
ld d, 0
ld e, c
add hl, de
ld a, (hl)
or a
jr z, .frec_found ; Found empty cell
; Try next cell (wrap around)
inc c
ld a, c
and %00111111 ; Wrap at 64
ld c, a
djnz .frec_loop
; No empty cells found
ld a, $ff
ret
.frec_found:
ld a, c ; Return cell index
ret
; ----------------------------------------------------------------------------
; Get Random
; ----------------------------------------------------------------------------
; Returns A = pseudo-random number using R register
get_random:
ld a, r ; R register changes every instruction
ld b, a
ld a, (random_seed)
add a, b
rlca
xor b
ld (random_seed), a
ret
random_seed: defb $5a ; Seed value
; ----------------------------------------------------------------------------
; Messages
; ----------------------------------------------------------------------------
msg_p1_wins: defb "P1 WINS!", 0
msg_p2_wins: defb "P2 WINS!", 0
msg_draw: defb "DRAW!", 0
msg_title: defb "INK WAR", 0
msg_mode1: defb "1 - TWO PLAYER", 0
msg_mode2: defb "2 - AI EASY", 0
msg_mode3: defb "3 - AI MEDIUM", 0
msg_mode4: defb "4 - AI HARD", 0
msg_continue: defb "PRESS ANY KEY", 0
; ----------------------------------------------------------------------------
; Variables
; ----------------------------------------------------------------------------
game_state: defb 0 ; 0=title, 1=playing, 2=results
game_mode: defb 0 ; 0=two player, 1=vs AI
ai_difficulty: defb 0 ; 0=easy, 1=medium, 2=hard
cursor_row: defb 0
cursor_col: defb 0
key_pressed: defb 0
last_key: defb 0 ; Previous frame's key for repeat detection
key_timer: defb 0 ; Countdown for key repeat delay
ai_timer: defb 0 ; Countdown before AI moves
current_player: defb 1
p1_count: defb 0
p2_count: defb 0
board_state: defs 64, 0
; ----------------------------------------------------------------------------
; End
; ----------------------------------------------------------------------------
end start
Try This: Add More Levels
You could add intermediate difficulties:
AI_VERY_EASY equ 0 ; Random
AI_EASY equ 1 ; Adjacent only
AI_MEDIUM equ 2 ; Adjacent + defense (no position)
AI_HARD equ 3 ; Full strategy
AI_EXPERT equ 4 ; Full strategy + look-ahead (future unit)More keys are available on the same keyboard row (key 5 = bit 4).
Try This: Display Difficulty
Show the current difficulty during gameplay:
; After drawing UI, show difficulty level
ld a, (ai_difficulty)
; ... display "EASY", "MEDIUM", or "HARD" ...This reminds players which AI they’re facing.
What You’ve Learnt
- Menu expansion — Adding options to existing UI
- Dispatch patterns — Branching based on configuration
- Code reuse — Leveraging existing algorithms for difficulty
- Player choice — Giving control over game challenge
What’s Next
In Unit 14, we’ll add sound effects — distinct sounds for claims, errors, and victory to give the game audio feedback.
What Changed
Unit 12 → Unit 13
+156-19
| 1 | 1 | ; ============================================================================ | |
| 2 | - | ; INK WAR - Unit 12: Corner and Edge Strategy | |
| 2 | + | ; INK WAR - Unit 13: AI Difficulty Levels | |
| 3 | 3 | ; ============================================================================ | |
| 4 | - | ; AI now values strategic positions. Corners get +2 bonus, edges get +1. | |
| 5 | - | ; Combined with adjacency scoring for smarter opening moves. | |
| 4 | + | ; Choose your challenge: Easy (random), Medium (adjacent), Hard (full strategy) | |
| 5 | + | ; Title screen now offers four options for different play styles. | |
| 6 | 6 | ; | |
| 7 | 7 | ; Controls: Q=Up, A=Down, O=Left, P=Right, SPACE=Claim | |
| 8 | - | ; 1=Two Player, 2=vs Computer (on title screen) | |
| 8 | + | ; 1=Two Player, 2=AI Easy, 3=AI Medium, 4=AI Hard | |
| 9 | 9 | ; ============================================================================ | |
| 10 | 10 | | |
| 11 | 11 | org 32768 | |
| ... | |||
| 73 | 73 | ; Game modes | |
| 74 | 74 | GM_TWO_PLAYER equ 0 | |
| 75 | 75 | GM_VS_AI equ 1 | |
| 76 | + | | |
| 77 | + | ; AI difficulty levels | |
| 78 | + | AI_EASY equ 0 ; Random moves | |
| 79 | + | AI_MEDIUM equ 1 ; Adjacent priority only | |
| 80 | + | AI_HARD equ 2 ; Full strategy (defense + position) | |
| 76 | 81 | | |
| 77 | 82 | ; AI timing | |
| 78 | 83 | AI_DELAY equ 25 ; Frames before AI moves (~0.5 sec) | |
| 79 | 84 | | |
| 80 | 85 | ; Title screen positions | |
| 81 | - | TITLE_ROW equ 8 | |
| 82 | - | TITLE_COL equ 12 ; "INK WAR" (7 chars) centred: (32-7)/2=12.5 | |
| 83 | - | MODE1_ROW equ 14 ; "1 - TWO PLAYER" | |
| 84 | - | MODE1_COL equ 9 ; (32-14)/2 = 9 | |
| 85 | - | MODE2_ROW equ 16 ; "2 - VS COMPUTER" | |
| 86 | - | MODE2_COL equ 8 ; (32-15)/2 = 8.5 | |
| 86 | + | TITLE_ROW equ 6 | |
| 87 | + | TITLE_COL equ 12 ; "INK WAR" (7 chars) centred | |
| 88 | + | MODE1_ROW equ 12 ; "1 - TWO PLAYER" | |
| 89 | + | MODE1_COL equ 9 | |
| 90 | + | MODE2_ROW equ 14 ; "2 - AI EASY" | |
| 91 | + | MODE2_COL equ 10 | |
| 92 | + | MODE3_ROW equ 16 ; "3 - AI MEDIUM" | |
| 93 | + | MODE3_COL equ 9 | |
| 94 | + | MODE4_ROW equ 18 ; "4 - AI HARD" | |
| 95 | + | MODE4_COL equ 10 | |
| 87 | 96 | | |
| 88 | 97 | ; Results screen positions | |
| 89 | 98 | CONTINUE_ROW equ 22 ; "PRESS ANY KEY" after results | |
| ... | |||
| 123 | 132 | ; ---------------------------------------------------------------------------- | |
| 124 | 133 | ; State: Title | |
| 125 | 134 | ; ---------------------------------------------------------------------------- | |
| 126 | - | ; Waits for 1 (Two Player) or 2 (vs Computer) | |
| 135 | + | ; Waits for 1 (Two Player), 2 (AI Easy), 3 (AI Medium), 4 (AI Hard) | |
| 127 | 136 | | |
| 128 | 137 | ROW_12345 equ $f7 ; Keyboard row for 1,2,3,4,5 | |
| 129 | 138 | | |
| 130 | 139 | state_title: | |
| 131 | - | ; Check for key 1 (Two Player) | |
| 140 | + | ; Read keyboard row for keys 1-5 | |
| 132 | 141 | ld a, ROW_12345 | |
| 133 | 142 | in a, (KEY_PORT) | |
| 143 | + | | |
| 144 | + | ; Check for key 1 (Two Player) | |
| 134 | 145 | bit 0, a ; Key 1 | |
| 135 | 146 | jr z, .st_two_player | |
| 136 | 147 | | |
| 137 | - | ; Check for key 2 (vs Computer) | |
| 148 | + | ; Check for key 2 (AI Easy) | |
| 138 | 149 | bit 1, a ; Key 2 | |
| 139 | - | jr z, .st_vs_ai | |
| 150 | + | jr z, .st_ai_easy | |
| 151 | + | | |
| 152 | + | ; Check for key 3 (AI Medium) | |
| 153 | + | bit 2, a ; Key 3 | |
| 154 | + | jr z, .st_ai_medium | |
| 155 | + | | |
| 156 | + | ; Check for key 4 (AI Hard) | |
| 157 | + | bit 3, a ; Key 4 | |
| 158 | + | jr z, .st_ai_hard | |
| 140 | 159 | | |
| 141 | 160 | jp main_loop ; No valid key - keep waiting | |
| 142 | 161 | | |
| ... | |||
| 146 | 165 | call start_game | |
| 147 | 166 | jp main_loop | |
| 148 | 167 | | |
| 149 | - | .st_vs_ai: | |
| 168 | + | .st_ai_easy: | |
| 169 | + | ld a, GM_VS_AI | |
| 170 | + | ld (game_mode), a | |
| 171 | + | ld a, AI_EASY | |
| 172 | + | ld (ai_difficulty), a | |
| 173 | + | call start_game | |
| 174 | + | jp main_loop | |
| 175 | + | | |
| 176 | + | .st_ai_medium: | |
| 177 | + | ld a, GM_VS_AI | |
| 178 | + | ld (game_mode), a | |
| 179 | + | ld a, AI_MEDIUM | |
| 180 | + | ld (ai_difficulty), a | |
| 181 | + | call start_game | |
| 182 | + | jp main_loop | |
| 183 | + | | |
| 184 | + | .st_ai_hard: | |
| 150 | 185 | ld a, GM_VS_AI | |
| 151 | 186 | ld (game_mode), a | |
| 187 | + | ld a, AI_HARD | |
| 188 | + | ld (ai_difficulty), a | |
| 152 | 189 | call start_game | |
| 153 | 190 | jp main_loop | |
| 154 | 191 | | |
| ... | |||
| 1329 | 1366 | ld e, TEXT_ATTR | |
| 1330 | 1367 | call print_message | |
| 1331 | 1368 | | |
| 1332 | - | ; Draw "2 - VS COMPUTER" | |
| 1369 | + | ; Draw "2 - AI EASY" | |
| 1333 | 1370 | ld b, MODE2_ROW | |
| 1334 | 1371 | ld c, MODE2_COL | |
| 1335 | 1372 | ld hl, msg_mode2 | |
| 1373 | + | ld e, TEXT_ATTR | |
| 1374 | + | call print_message | |
| 1375 | + | | |
| 1376 | + | ; Draw "3 - AI MEDIUM" | |
| 1377 | + | ld b, MODE3_ROW | |
| 1378 | + | ld c, MODE3_COL | |
| 1379 | + | ld hl, msg_mode3 | |
| 1380 | + | ld e, TEXT_ATTR | |
| 1381 | + | call print_message | |
| 1382 | + | | |
| 1383 | + | ; Draw "4 - AI HARD" | |
| 1384 | + | ld b, MODE4_ROW | |
| 1385 | + | ld c, MODE4_COL | |
| 1386 | + | ld hl, msg_mode4 | |
| 1336 | 1387 | ld e, TEXT_ATTR | |
| 1337 | 1388 | call print_message | |
| 1338 | 1389 | | |
| ... | |||
| 1380 | 1431 | ; ---------------------------------------------------------------------------- | |
| 1381 | 1432 | ; AI Make Move | |
| 1382 | 1433 | ; ---------------------------------------------------------------------------- | |
| 1383 | - | ; AI picks best adjacent cell (or random if none) | |
| 1434 | + | ; AI picks a cell based on difficulty level | |
| 1384 | 1435 | | |
| 1385 | 1436 | ai_make_move: | |
| 1386 | - | ; Find best cell adjacent to AI territory | |
| 1437 | + | ; Dispatch based on difficulty | |
| 1438 | + | ld a, (ai_difficulty) | |
| 1439 | + | or a | |
| 1440 | + | jr z, .aim_easy ; AI_EASY = 0 | |
| 1441 | + | cp AI_MEDIUM | |
| 1442 | + | jr z, .aim_medium | |
| 1443 | + | ; AI_HARD - full strategy | |
| 1387 | 1444 | call find_best_adjacent_cell | |
| 1445 | + | jr .aim_have_cell | |
| 1446 | + | | |
| 1447 | + | .aim_easy: | |
| 1448 | + | ; Random moves | |
| 1449 | + | call find_random_empty_cell | |
| 1450 | + | jr .aim_have_cell | |
| 1451 | + | | |
| 1452 | + | .aim_medium: | |
| 1453 | + | ; Adjacent priority only (no defense/position) | |
| 1454 | + | call find_adjacent_only | |
| 1455 | + | ; Fall through to .aim_have_cell | |
| 1456 | + | | |
| 1457 | + | .aim_have_cell: | |
| 1388 | 1458 | ; A = cell index (0-63), or $FF if board full | |
| 1389 | 1459 | | |
| 1390 | 1460 | cp $ff | |
| ... | |||
| 1515 | 1585 | | |
| 1516 | 1586 | best_cell: defb 0 | |
| 1517 | 1587 | best_score: defb 0 | |
| 1588 | + | | |
| 1589 | + | ; ---------------------------------------------------------------------------- | |
| 1590 | + | ; Find Adjacent Only (Medium Difficulty) | |
| 1591 | + | ; ---------------------------------------------------------------------------- | |
| 1592 | + | ; Returns A = index of empty cell with most AI neighbors, or $FF if none | |
| 1593 | + | ; Only considers AI adjacency - no defense or position bonus | |
| 1594 | + | | |
| 1595 | + | find_adjacent_only: | |
| 1596 | + | ; Initialize best tracking | |
| 1597 | + | ld a, $ff | |
| 1598 | + | ld (best_cell), a | |
| 1599 | + | xor a | |
| 1600 | + | ld (best_score), a | |
| 1601 | + | | |
| 1602 | + | ; Scan all 64 cells | |
| 1603 | + | ld c, 0 | |
| 1604 | + | | |
| 1605 | + | .fao_loop: | |
| 1606 | + | ; Check if cell is empty | |
| 1607 | + | ld hl, board_state | |
| 1608 | + | ld d, 0 | |
| 1609 | + | ld e, c | |
| 1610 | + | add hl, de | |
| 1611 | + | ld a, (hl) | |
| 1612 | + | or a | |
| 1613 | + | jr nz, .fao_next | |
| 1614 | + | | |
| 1615 | + | ; Empty cell - count adjacent AI cells only | |
| 1616 | + | push bc | |
| 1617 | + | ld a, c | |
| 1618 | + | call count_adjacent_ai | |
| 1619 | + | pop bc | |
| 1620 | + | | |
| 1621 | + | ; Compare with best score | |
| 1622 | + | ld b, a | |
| 1623 | + | ld a, (best_score) | |
| 1624 | + | cp b | |
| 1625 | + | jr nc, .fao_next | |
| 1626 | + | | |
| 1627 | + | ; New best found | |
| 1628 | + | ld a, b | |
| 1629 | + | ld (best_score), a | |
| 1630 | + | ld a, c | |
| 1631 | + | ld (best_cell), a | |
| 1632 | + | | |
| 1633 | + | .fao_next: | |
| 1634 | + | inc c | |
| 1635 | + | ld a, c | |
| 1636 | + | cp 64 | |
| 1637 | + | jr c, .fao_loop | |
| 1638 | + | | |
| 1639 | + | ; Check if we found an adjacent cell | |
| 1640 | + | ld a, (best_score) | |
| 1641 | + | or a | |
| 1642 | + | jr z, .fao_random | |
| 1643 | + | | |
| 1644 | + | ; Return best adjacent cell | |
| 1645 | + | ld a, (best_cell) | |
| 1646 | + | ret | |
| 1647 | + | | |
| 1648 | + | .fao_random: | |
| 1649 | + | ; Fall back to random empty cell | |
| 1650 | + | call find_random_empty_cell | |
| 1651 | + | ret | |
| 1518 | 1652 | | |
| 1519 | 1653 | ; ---------------------------------------------------------------------------- | |
| 1520 | 1654 | ; Get Position Bonus | |
| ... | |||
| 1818 | 1952 | msg_draw: defb "DRAW!", 0 | |
| 1819 | 1953 | msg_title: defb "INK WAR", 0 | |
| 1820 | 1954 | msg_mode1: defb "1 - TWO PLAYER", 0 | |
| 1821 | - | msg_mode2: defb "2 - VS COMPUTER", 0 | |
| 1955 | + | msg_mode2: defb "2 - AI EASY", 0 | |
| 1956 | + | msg_mode3: defb "3 - AI MEDIUM", 0 | |
| 1957 | + | msg_mode4: defb "4 - AI HARD", 0 | |
| 1822 | 1958 | msg_continue: defb "PRESS ANY KEY", 0 | |
| 1823 | 1959 | | |
| 1824 | 1960 | ; ---------------------------------------------------------------------------- | |
| ... | |||
| 1827 | 1963 | | |
| 1828 | 1964 | game_state: defb 0 ; 0=title, 1=playing, 2=results | |
| 1829 | 1965 | game_mode: defb 0 ; 0=two player, 1=vs AI | |
| 1966 | + | ai_difficulty: defb 0 ; 0=easy, 1=medium, 2=hard | |
| 1830 | 1967 | cursor_row: defb 0 | |
| 1831 | 1968 | cursor_col: defb 0 | |
| 1832 | 1969 | key_pressed: defb 0 |