millfork/examples/nes/pong.mfk

// Taken from Nerdy Nights Week 7's pong example game
// (http://nintendoage.com/forum/messageview.cfm?catid=22&threadid=8747)
//
// Original example made by bunnyboy of nintendoage.com
// Millfork adaptation by Garydos (https://github.com/Garydos)
//
// compile with -t nes_small

import random
import nes_joy

// *STRUCT DEFINTIONS*

struct Ball {
    byte x,      // ball horizontal position
    byte y,      // ball vertical position
    byte up,     // 1 = ball moving up
    byte down,   // 1 = ball moving down
    byte left,   // 1 = ball moving left
    byte right,  // 1 = ball moving right
    byte speedx, // ball horizontal speed per frame
    byte speedy  // ball vertical speed per frame
}

struct Sprite { //NES hardware sprite layout
    byte y,         // Y Coordinate - 1
    byte tile,      // tile index #
    byte attrs,     // attributes
    byte x          // X Coordinate
}

struct Paddle_Sprs {
    Sprite paddletop,
    Sprite paddlebody1,
    Sprite paddlebody2,
    Sprite paddlebottom
}

// *VARIABLES*

byte paddle1ytop   // player 1 paddle top vertical position
byte paddle2ytop   // player 2 paddle bottom vertical position
byte score1     // player 1 score, 0-15
byte score2     // player 2 score, 0-15
Ball ball       // the ball
array oam_buffer [256] @$200 // sprite buffer
Sprite ball_spr @$200   //  ball's sprite
Paddle_Sprs left_paddle_sprs @$204 //  left paddle's sprites
Paddle_Sprs right_paddle_sprs @$214 // right paddle's sprites
word framecounter   // counts the amount of frames that have passed

volatile Gamestate gamestate // the current Gamestate


// *CONSTANTS*

enum Gamestate {
    STATETITLE, // displaying title screen
    STATEPLAYING, // move paddles/ball, check for collisions
    STATEGAMEOVER // displaying game over screen
}

const byte RIGHTWALL      = $F4  // when ball reaches one of these, do something
const byte TOPWALL        = $18
const byte BOTTOMWALL     = $B0
const byte LEFTWALL       = $04
  
const byte PADDLE1X       = $08  // horizontal position for paddles, doesnt move
const byte PADDLE2X       = $F0

const byte PADDLEHEIGHT   = $20  // height of each paddle in pixels

// sprite tiles used by the paddles
const byte PADDLETOPBOTSPR = $00
const byte PADDLEBODYSPR = $01

// sprite attributes used by the paddles
const byte PADDLESPRATTR = $01
const byte PADDLESPRATTRHFLIP = $41
const byte PADDLESPRATTRVFLIP = $81
const byte PADDLESPRATTRHVFLIP = $C1

// sprite tiles and attributes used by the ball
const byte BALLSPRATTR = $01
const byte BALLSPR = $02

// vram locations declared as constants for readability/convenience
// *note that these do not correlate to CPU ram locations*
const word ppu_pallete_ram = $3F00
const word ppu_nametable_ram = $2000
const word ppu_nametable_0_attr_ram = $23C0


void main() {
    //Set starting game state
    gamestate = STATETITLE
    //prepare the title screen gamestate
    game_title_init()
    while(true){} // all work is done in NMI
}

void nmi() {
    //Push sprite information to the PPU through DMA transfer
    ppu_oam_dma_write(oam_buffer.addr.hi)
    
    //Run graphics updates + game logic specific to each gamestate
    main_game_logic()
}

void irq() {
    
}

inline void main_game_logic() {
    // use a return dispatch here
    // to use different logic for each screen/gamestate
    return [gamestate] {
        STATETITLE    @ game_title_logic
        STATEPLAYING  @ game_playing_logic
        STATEGAMEOVER @ game_gameover_logic
    }
}

void game_title_init() {
    byte i
    //for now, turn off the screen and nmi
    ppu_ctrl = 0
    ppu_mask = 0
    
    //initialize the sprites and palletes
    init_graphics()
    
    //write a full screen of background data
    
    load_sky_background()
    
    //write the title screen message
    read_ppu_status() // read PPU status to reset the high/low latch
    ppu_set_addr(ppu_nametable_ram+$018B) // point the PPU to the message's start
    for i,0,until,$0B {
        ppu_write_data(title_msg[i])
    }
    
    //write the border
    //top border
    read_ppu_status() // read PPU status to reset the high/low latch
    ppu_set_addr(ppu_nametable_ram+$0020)
    for i,0,until,$20 {
        ppu_write_data($01)
    }
    //bottom border
    read_ppu_status() // read PPU status to reset the high/low latch
    ppu_set_addr(ppu_nametable_ram+$0380)
    for i,0,until,$20 {
        ppu_write_data($01)
    }
    
    //set ppu address increment to 32 so we can draw the left and right borders
    //(allows us to draw to the nametable in vertical strips rather than horizontal)
    ppu_ctrl = %00000100
    
    //left border
    read_ppu_status() // read PPU status to reset the high/low latch
    ppu_set_addr(ppu_nametable_ram)
    for i,0,until,$20 {
        ppu_write_data($01)
    }
    //right border
    read_ppu_status() // read PPU status to reset the high/low latch
    ppu_set_addr(ppu_nametable_ram+$1F)
    for i,0,until,$20 {
        ppu_write_data($01)
    }
    

    framecounter = 0
    ppu_set_scroll(0,0)
    ppu_wait_vblank() //wait for next vblank before re-enabling NMI
                      //so that we don't get messed up scroll registers
    //re-enable the screen and nmi
    ppu_ctrl = %10010000   // enable NMI, sprites from Pattern Table 0, background from Pattern Table 1
    ppu_mask = %00011110   // enable sprites, enable background, no clipping on left side
}

void game_title_logic() {
    read_joy1()
    if input_start != 0 {
        rand_seed = framecounter //seed the random number generator with the amount of frames
            //that have passed since the title screen was shown
        gamestate = STATEPLAYING
        game_playing_init()
        return
    }
    framecounter += 1
}

inline asm void ppu_wait_vblank() {
    vblankwait:
        BIT $2002
        ! BPL vblankwait
    ? RTS
}

void game_playing_init() {
    //for now, turn off the screen and nmi
    ppu_ctrl = 0
    ppu_mask = 0
    
    //write a full screen of data
    load_sky_background()
    draw_score_text_background()
    draw_boundaries_background()
    load_play_attribute_table()
    //initialize the game
    init_game()
    reset_ball()
    
    ppu_set_scroll(0,0)
    ppu_wait_vblank() //wait for next vblank before re-enabling NMI
                      //so that we don't get messed up scroll registers
    //re-enable the screen and nmi
    ppu_ctrl = %10010000   // enable NMI, sprites from Pattern Table 0, background from Pattern Table 1
    ppu_mask = %00011110   // enable sprites, enable background, no clipping on left side
}

void game_playing_logic() {
    draw_score()
    //update scroll last because writes to vram also
    //overwrite the scroll register
    ppu_set_scroll(0,0)    // tell the ppu there is no background scrolling
    
    move_ball()
    move_paddles()
    check_paddle_collision()
    update_sprites()
    if score1 >= 15 || score2 >= 15{
        //Someone's reached 15 points, the game is over,
        //so set the state to game over and reset the
        //framecounter
        gamestate = STATEGAMEOVER
        
        //move all the sprites off screen
        //in preperation for the gameover screen
        ball_spr.y = $ef
        
        left_paddle_sprs.paddletop.y = $ef
        left_paddle_sprs.paddlebody1.y = $ef
        left_paddle_sprs.paddlebody2.y = $ef
        left_paddle_sprs.paddlebottom.y = $ef
        
        right_paddle_sprs.paddletop.y = $ef
        right_paddle_sprs.paddlebody1.y = $ef
        right_paddle_sprs.paddlebody2.y = $ef
        right_paddle_sprs.paddlebottom.y = $ef
        
        game_gameover_init()
    }
}

void game_gameover_init() {
    //for now, turn off nmi and sprites
    ppu_ctrl = 0
    ppu_mask = 0
    
    draw_score() //draw the final score
    draw_game_over_screen() //draw the game over message
    
    framecounter = 0
    ppu_set_scroll(0,0)    // tell the ppu there is no background scrolling
    ppu_wait_vblank() //wait for next vblank before re-enabling NMI
                      //so that we don't get messed up scroll registers
    //re-enable the screen and nmi
    ppu_ctrl = %10010000   // enable NMI, sprites from Pattern Table 0, background from Pattern Table 1
    ppu_mask = %00011110   // enable sprites, enable background, no clipping on left side
}

void game_gameover_logic() {
    if framecounter >= 240{
        //3 seconds have passed,
        //reset the game
        simulate_reset()
    }
    framecounter += 1
}

void move_ball() {
    if ball.up == 1 {
        ball.y -= ball.speedy
        if ball.y <= TOPWALL {
            //bounce, ball now moving down
            ball.down = 1
            ball.up = 0
        }
    }
    else if ball.down == 1 {
        ball.y += ball.speedy
        if ball.y + 8 >= BOTTOMWALL {
            //bounce, ball now moving up
            ball.down = 0
            ball.up = 1
        }
    }
    
    if ball.right == 1 {
        ball.x += ball.speedx
        if ball.x >= RIGHTWALL {
            // ball has gone past a paddle and hit the right wall
            // give player1 a point and reset the ball
            score1 += 1
            reset_ball()
        }
    }
    else if ball.left == 1 {
        ball.x -= ball.speedx
        if ball.x <= LEFTWALL {
            // ball has gone past a paddle and hit the left wall
            // give player2 a point and reset the ball
            score2 += 1
            reset_ball()
        }
    }
}

void move_paddles() {
    // Player 1 controls
    read_joy1()
    if input_dy < 0 {  // Up button
        if paddle1ytop > TOPWALL {
            paddle1ytop -= 1
        }
    }
    else if input_dy > 0 { // Down button
        if (paddle1ytop + PADDLEHEIGHT) < BOTTOMWALL {
            paddle1ytop += 1
        }
    }
    
    // Player 2 controls
    read_joy2()
    if input_dy < 0 {  // Up button
        if paddle2ytop > TOPWALL {
            paddle2ytop -= 1
        }
    }
    else if input_dy > 0 { // Down button
        if (paddle2ytop + PADDLEHEIGHT) < BOTTOMWALL {
            paddle2ytop += 1
        }
    }
}

void check_paddle_collision() {
    //Check left paddle collision
    if ball.x <= PADDLE1X+8 && ball.y >= paddle1ytop && ball.y <= paddle1ytop + PADDLEHEIGHT {
        //bounce the ball back, move it right
        ball.left = 0
        ball.right = 1
    }
    
    //Check right paddle collision
    if ball.x >= PADDLE2X-8 && ball.y >= paddle2ytop && ball.y <= paddle2ytop + PADDLEHEIGHT {
        //bounce the ball back, move it left
        ball.left = 1
        ball.right = 0
    }
}

inline void init_graphics() {
    init_sprites()
    load_palletes()
}

macro void load_palletes() {
    byte i
    read_ppu_status() // read PPU status to reset the high/low latch
    ppu_set_addr(ppu_pallete_ram) // point the PPU to palette ram
    for i,0,until,$20 {
        ppu_write_data(pallete[i])
    }
}

inline void load_sky_background() {
    word xx
    read_ppu_status() // read PPU status to reset the high/low latch
    ppu_set_addr(ppu_nametable_ram) // point the PPU to palette ram
    for xx,0,until,$0400 {
        ppu_write_data($00) // $00 = sky
    }
}

macro void draw_score_text_background() {
    byte i
    read_ppu_status() // read PPU status to reset the high/low latch
    ppu_set_addr(ppu_nametable_ram+$20) // point the PPU to score text's start
    for i,0,until,$1C {
        ppu_write_data(scorebackground[i])
    }
}

macro void draw_boundaries_background() {
    byte i
    
    //draw top boundary
    read_ppu_status() // read PPU status to reset the high/low latch
    ppu_set_addr(ppu_nametable_ram+$40) // point the PPU to the top boundary's start
    for i,0,until,$20 {
        ppu_write_data($81) //write the top boundary tile
    }
    
    //draw bottom boundary
    read_ppu_status() // read PPU status to reset the high/low latch
    ppu_set_addr(ppu_nametable_ram+$02C0) // point the PPU to the top boundary's start
    for i,0,until,$20 {
        ppu_write_data($80) //write the bottom boundary tile
    }
}

void draw_game_over_screen() {
    byte i
    
    //draw the static game over message
    read_ppu_status() // read PPU status to reset the high/low latch
    ppu_set_addr(ppu_nametable_ram+$0107) // point the PPU to the message's start
    for i,0,until,$12 {
        ppu_write_data(gameover_msg[i])
    }
    //draw the win message
    read_ppu_status() // read PPU status to reset the high/low latch
    ppu_set_addr(ppu_nametable_ram+$01AC) // point the PPU to the message's start
    if score1 >= score2 {
        for i,0,until,$0B {
            ppu_write_data(p1_win_msg[i])
        }
    }
    else {
        for i,0,until,$0B {
            ppu_write_data(p2_win_msg[i])
        }
    }
}

void draw_p1_win_msg() {
    byte i
    read_ppu_status() // read PPU status to reset the high/low latch
    ppu_set_addr(ppu_nametable_ram+$0140) // point the PPU to the message's start
    for i,0,until,$20 {
        ppu_write_data(p1_win_msg[i])
    }
}

void draw_p2_win_msg() {
    byte i
    read_ppu_status() // read PPU status to reset the high/low latch
    ppu_set_addr(ppu_nametable_ram+$0140) // point the PPU to the message's start
    for i,0,until,$20 {
        ppu_write_data(p2_win_msg[i])
    }
}

macro void load_play_attribute_table() {
    byte i
    read_ppu_status() // read PPU status to reset the high/low latch
    ppu_set_addr(ppu_nametable_0_attr_ram) // point the PPU to nametable 0's attribute table
    for i,0,until,$10 {
        ppu_write_data(attribute[i])
    }
}

void init_sprites() {
    byte i
    for i,0,to,255 {
        if (i & %00000011) == 0 {
            //each sprite takes up 4 bytes, and we want to edit
            //the y position of each sprite (0th byte)
            //so we use the %00000011 mask to write every 4th byte (every 0th sprite byte)
            
            oam_buffer[i] = $ef // move the sprite off screen
        }
        else {
            oam_buffer[i] = 0
        }
    }
}

void init_game() {
    //Set some initial ball stats
    ball.down = $00
    ball.right = $01
    ball.up = $00
    ball.left = $00
    ball.y = $50
    ball.x = $80
    ball.speedx = $02
    ball.speedy = $02
    
    //Set initial paddle states
    paddle1ytop = $70
    paddle2ytop = $70
}

void update_sprites() {
    //Update ball sprite
    ball_spr.y = ball.y
    ball_spr.tile = BALLSPR
    ball_spr.attrs = BALLSPRATTR
    ball_spr.x = ball.x
    
    //update paddle sprites
    
    // update top of left paddle
    left_paddle_sprs.paddletop.y = paddle1ytop
    left_paddle_sprs.paddletop.tile = PADDLETOPBOTSPR
    left_paddle_sprs.paddletop.attrs = PADDLESPRATTRVFLIP
    left_paddle_sprs.paddletop.x = PADDLE1X

    // update body of left paddle
    left_paddle_sprs.paddlebody1.y = paddle1ytop + 8
    left_paddle_sprs.paddlebody1.tile = PADDLEBODYSPR
    left_paddle_sprs.paddlebody1.attrs = PADDLESPRATTRVFLIP
    left_paddle_sprs.paddlebody1.x = PADDLE1X
    
    left_paddle_sprs.paddlebody2.y = paddle1ytop + 16
    left_paddle_sprs.paddlebody2.tile = PADDLEBODYSPR
    left_paddle_sprs.paddlebody2.attrs = PADDLESPRATTRVFLIP
    left_paddle_sprs.paddlebody2.x = PADDLE1X
  
    // update bottom of left paddle
    left_paddle_sprs.paddlebottom.y = paddle1ytop + 24
    left_paddle_sprs.paddlebottom.tile = PADDLETOPBOTSPR
    left_paddle_sprs.paddlebottom.attrs = PADDLESPRATTR
    left_paddle_sprs.paddlebottom.x = PADDLE1X
    
    // update top of right paddle
    right_paddle_sprs.paddletop.y = paddle2ytop
    right_paddle_sprs.paddletop.tile = PADDLETOPBOTSPR
    right_paddle_sprs.paddletop.attrs = PADDLESPRATTRHVFLIP
    right_paddle_sprs.paddletop.x = PADDLE2X

    // update body of right paddle
    right_paddle_sprs.paddlebody1.y = paddle2ytop + 8
    right_paddle_sprs.paddlebody1.tile = PADDLEBODYSPR
    right_paddle_sprs.paddlebody1.attrs = PADDLESPRATTRHVFLIP
    right_paddle_sprs.paddlebody1.x = PADDLE2X
    
    right_paddle_sprs.paddlebody2.y = paddle2ytop + 16
    right_paddle_sprs.paddlebody2.tile = PADDLEBODYSPR
    right_paddle_sprs.paddlebody2.attrs = PADDLESPRATTRHVFLIP
    right_paddle_sprs.paddlebody2.x = PADDLE2X
  
    // update bottom of right paddle
    right_paddle_sprs.paddlebottom.y = paddle2ytop + 24
    right_paddle_sprs.paddlebottom.tile = PADDLETOPBOTSPR
    right_paddle_sprs.paddlebottom.attrs = PADDLESPRATTRHFLIP
    right_paddle_sprs.paddlebottom.x = PADDLE2X
}

inline void draw_score() {
    byte digit01
    byte digit10
    read_ppu_status() // read PPU status to reset the high/low latch
    
    //display player1's score
    digit01 = score1 %% 10 //get the ones digit
    digit10 = score1 / 10  //get the tens digit
    digit10 %%= 10
    
    ppu_set_addr(ppu_nametable_ram+$29) // point the PPU to player1's score number
    if digit10 > 0 {
        ppu_write_data(digit10 + '0')
    }
    ppu_write_data(digit01 + '0')
    
    //display player2's score
    digit01 = score2 %% 10 //get the ones digit
    digit10 = score2 / 10  //get the tens digit
    digit10 %%= 10
    
    ppu_set_addr(ppu_nametable_ram+$3C) // point the PPU to player2's score number
    if digit10 > 0 {
        ppu_write_data(digit10 + '0')
    }
    ppu_write_data(digit01 + '0')
}

void reset_ball() {
    byte dir
                
    //randomize up/down motion
    dir = rand()
    dir = dir & %00000001 // dir is now either 0 or 1
    ball.down = dir
    ball.up = dir ^ %00000001 //flip the bit
    
    //randomize left/right motion
    dir = rand()
    dir = dir & %00000001 // dir is now either 0 or 1
    ball.right = dir
    ball.left = dir ^ %00000001 //flip the bit
    
    //reset the ball to the center and set its speed
    ball.y = $50
    ball.x = $80
    ball.speedx = $02
    ball.speedy = $02
}

//  *LEVEL GRAPHICS*

//palletes for entire game (both title and play screens)
const array pallete = [
  $22,$29,$1A,$0F,  $22,$36,$17,$0F,  $22,$30,$21,$0F,  $22,$27,$17,$0F, //background palette
  $22,$1C,$15,$14,  $22,$02,$38,$3C,  $22,$1C,$15,$14,  $22,$02,$38,$3C //sprite palette
]

const array scorebackground = "P1 Score-          P2 Score-" ascii
const array gameover_msg = "G A M E    O V E R" ascii
const array p1_win_msg =   "P1    Wins!" ascii
const array p2_win_msg =   "P2    Wins!" ascii
const array title_msg = "Press Start" ascii

//attribute table for play screen graphics
const array attribute = [
  %00000101, %00000101, %00000101, %00000101, %00000101, %00000101, %00000101, %00000101,
  %00000101, %00000101, %00000101, %00000101, %00000101, %00000101, %00000101, %00000101,
  %00000101, %00000101, %00000101, %00000101, %00000101, %00000101, %00000101, %00000101
]


//  *CHARACTER ROM (GRAPHICS)*
segment(chrrom) const array graphics @ $0000 = file("tiles.chr", 0)