SixtyPical/eg/c64/demo-game.60p

// ****************************
// * Demo Game for SixtyPical *
// ****************************

// ----------------------------------------------------------------
// Type Definitions
// ----------------------------------------------------------------

//
// Type of routines (and vectors to those routines) which are called on each frame
// to implement a certain state of the game (title screen, in play, game over, etc.)
//
// This type is also used as the type for the interrupt vector, even though
// the interrupt routine saves and restores everything before being called and
// thus clearly does not actually trash all the registers.  It is declared this
// way so that the game state routines, which do trash these registers, can be
// assigned to it.
//
// This type is also used as the type for the location the old interrupt vector
// is backed up to, because all the game state routines `goto` the old handler
// and the end of their own routines, so the type needs to be compatible.
// (In a good sense, it is a continuation.)
//
// Further,
//
// It's very arguable that screen1/2/3/4 and colormap1/2/3/4 are not REALLY inputs.
// They're only there to support the fact that game states sometimes clear the
// screen, and sometimes don't.  When they don't, they preserve the screen, and
// currently the way to say "we preserve the screen" is to have it as both input
// and output.  There is probably a better way to do this, but it needs thought.
//

typedef routine
  inputs joy2, press_fire_msg, dispatch_game_state,
         actor_pos, actor_delta, actor_logic,
         screen, screen1, screen2, screen3, screen4, colormap1, colormap2, colormap3, colormap4
  outputs dispatch_game_state,
          actor_pos, actor_delta, actor_logic,
          screen, screen1, screen2, screen3, screen4, colormap1, colormap2, colormap3, colormap4
  trashes a, x, y, c, z, n, v, pos, new_pos, delta, ptr, dispatch_logic
    game_state_routine

//
// Routines that are called to get the new state of each actor (player, enemy, etc.)
//
// Routines that conform to this type also follow this convention:
//
// Set carry if the player perished.  Carry clear otherwise.
//

typedef routine
  inputs pos, delta, joy2, screen
  outputs pos, delta, new_pos, screen, c
  trashes a, x, y, z, n, v, ptr
    logic_routine

// ----------------------------------------------------------------
// System Locations
// ----------------------------------------------------------------

byte vic_border @ 53280
byte vic_bg @ 53281

byte table[256] screen1 @ 1024
byte table[256] screen2 @ 1274
byte table[256] screen3 @ 1524
byte table[256] screen4 @ 1774

byte table[256] colormap1 @ 55296
byte table[256] colormap2 @ 55546
byte table[256] colormap3 @ 55796
byte table[256] colormap4 @ 56046

buffer[2048] screen @ 1024
byte joy2 @ $dc00

// ----------------------------------------------------------------
// Global Variables
// ----------------------------------------------------------------

pointer ptr @ 254

word table[256] actor_pos
word pos
word new_pos

word table[256] actor_delta
word delta

vector logic_routine table[256] actor_logic
vector logic_routine dispatch_logic

byte table[32] press_fire_msg: "PRESS`FIRE`TO`PLAY"

//
// Points to the routine that implements the current game state.
//

vector game_state_routine
  dispatch_game_state

//
// Interrupt vector.  Has same type as game states (see above.)
//

vector game_state_routine
  cinv @ 788

//
// Location to which the old interrupt vector is saved before replacement.
//

vector game_state_routine
  save_cinv

// ----------------------------------------------------------------
// Utility Routines
// ----------------------------------------------------------------

routine read_stick
  inputs joy2
  outputs delta
  trashes a, x, z, n
{
    ld x, joy2
    ld a, x
    and a, 1                   // up
    if z {
        copy $ffd8, delta      // -40
    } else {
        ld a, x
        and a, 2               // down
        if z {
            copy word 40, delta
        } else {
            ld a, x
            and a, 4               // left
            if z {
                copy $ffff, delta  // -1
            } else {
                ld a, x
                and a, 8           // right
                if z {
                    copy word 1, delta
                } else {
                    copy word 0, delta
                }
            }
        }
    }
}

// You can repeatedly (i.e. as part of actor logic or an IRQ handler)
// call this routine.
// Upon return, if carry is set, the button was pressed then released.

define check_button routine
  inputs joy2
  outputs c
  trashes a, z, n
  static byte button_down : 0
{
    ld a, button_down
    if z {
        ld a, joy2
        and a, $10
        if z {
            ld a, 1
            st a, button_down
        }
        st off, c
    } else {
        ld a, joy2
        and a, $10
        if not z {
            ld a, 0
            st a, button_down
            st on, c
        } else {
            st off, c
        }
    }
}

routine clear_screen
  outputs screen1, screen2, screen3, screen4, colormap1, colormap2, colormap3, colormap4
  trashes a, y, c, n, z
{
    ld y, 0
    repeat {
        ld a, 1
        st a, colormap1 + y
        st a, colormap2 + y
        st a, colormap3 + y
        st a, colormap4 + y

        ld a, 32
        st a, screen1 + y
        st a, screen2 + y
        st a, screen3 + y
        st a, screen4 + y

        inc y
        cmp y, 250
    } until z
}

routine calculate_new_position
  inputs pos, delta
  outputs new_pos
  trashes a, c, n, z, v
{
    copy pos, new_pos
    st off, c
    add new_pos, delta
}

define check_new_position_in_bounds routine
  inputs new_pos
  outputs c
  trashes a, z, n, v
  static word compare_target : 0
{
    copy 1000, compare_target
    st on, c
    sub compare_target, new_pos

    if not c {
        copy word 0, compare_target
        st on, c
        sub compare_target, new_pos
        if not c {
            st off, c
        } else {
            st on, c
        }
    } else {
        st on, c
    }
}

routine init_game
  inputs actor_pos, actor_delta, actor_logic
  outputs actor_pos, actor_delta, actor_logic
  trashes pos, a, y, z, n, c, v
{
    ld y, 0
    copy word 0, pos
    repeat {
        copy pos, actor_pos + y
        copy word 40, actor_delta + y
        copy enemy_logic, actor_logic + y

        st off, c
        add pos, word 7

        inc y
        cmp y, 16
    } until z

    ld y, 0
    copy word 0, actor_pos + y
    copy word 0, actor_delta + y
    copy player_logic, actor_logic + y
}

// ----------------------------------------------------------------
// Actor Logics
// ----------------------------------------------------------------

define player_logic logic_routine
{
    call read_stick

    call calculate_new_position
    call check_new_position_in_bounds

    if c {
        copy ^screen, ptr
        st off, c
        add ptr, new_pos
        ld y, 0

        // check collision.
        ld a, [ptr] + y
        // if "collision" is with your own self, treat it as if it's blank space!
        cmp a, 81
        if z {
            ld a, 32
        }
        cmp a, 32
        if z {
            copy ^screen, ptr
            st off, c
            add ptr, pos
            copy 32, [ptr] + y

            copy new_pos, pos

            copy ^screen, ptr
            st off, c
            add ptr, pos
            copy 81, [ptr] + y

            st off, c
        } else {
            st on, c
        }

        // FIXME these trashes, strictly speaking, probably shouldn't be needed,
        // but currently the compiler cares a little too much about values that are
        // initialized in one branch of an `if`, but not the other, but are trashed
        // at the end of the routine anyway.
        trash ptr
        trash y
        trash v
    } else {
        st off, c
    }
}

define enemy_logic logic_routine
  static word compare_target : 0
{
    call calculate_new_position
    call check_new_position_in_bounds

    if c {
        copy ^screen, ptr
        st off, c
        add ptr, new_pos
        ld y, 0

        // check collision.
        ld a, [ptr] + y
        // if "collision" is with your own self, treat it as if it's blank space!
        cmp a, 82
        if z {
            ld a, 32
        }
        cmp a, 32
        if z {
            copy ^screen, ptr
            st off, c
            add ptr, pos
            copy 32, [ptr] + y

            copy new_pos, pos

            copy ^screen, ptr
            st off, c
            add ptr, pos
            copy 82, [ptr] + y

            st off, c
        } else {
            st on, c
        }

        // FIXME these trashes, strictly speaking, probably shouldn't be needed,
        // but currently the compiler cares too much about values that are
        // initialized in one branch of an `if`, but not the other, but trashed
        // at the end of the routine anyway.
        trash ptr
        trash y
    } else {
        copy delta, compare_target
        st on, c
        sub compare_target, word 40
        if not z {
            copy word 40, delta
        } else {
            copy $ffd8, delta
        }
    }

    st off, c
}

// ----------------------------------------------------------------
// Game States
// ----------------------------------------------------------------

define game_state_title_screen game_state_routine
{
    ld y, 0
    repeat {

        // First we "clip" the index to 0-31 to ensure we don't
        // read outside the bounds of the table:
        ld a, y
        and a, 31
        ld y, a

        ld a, press_fire_msg + y

        st on, c
        sub a, 64   // yuck.  oh well

        st a, screen1 + y
        inc y
        cmp y, 18
    } until z

    st off, c
    call check_button

    if c {
        call clear_screen
        call init_game
        copy game_state_play, dispatch_game_state
    }

    goto save_cinv
}

define game_state_play game_state_routine
static byte save_x : 0
{
    ld x, 0
    repeat {
        copy actor_pos + x, pos
        copy actor_delta + x, delta

        st x, save_x

        copy actor_logic + x, dispatch_logic
        call dispatch_logic

        if c {
            // Player died!  Want no dead!  Break out of the loop (this is a bit awkward.)
            call clear_screen
            copy game_state_game_over, dispatch_game_state
            ld x, 15
        } else {
            ld x, save_x
        }

        copy pos, actor_pos + x
        copy delta, actor_delta + x

        inc x
        cmp x, 16
    } until z

    goto save_cinv
}

define game_state_game_over game_state_routine
{
    st off, c
    call check_button

    if c {
        call clear_screen
        call init_game
        copy game_state_title_screen, dispatch_game_state
    }

    goto save_cinv
}

// *************************
// * Main Game Loop Driver *
// *************************

define our_cinv game_state_routine
{
    goto dispatch_game_state
}

routine main
  inputs cinv
  outputs cinv, save_cinv, pos, dispatch_game_state,
          screen1, screen2, screen3, screen4, colormap1, colormap2, colormap3, colormap4
  trashes a, y, n, c, z, vic_border, vic_bg
{
    ld a, 5
    st a, vic_border
    ld a, 0
    st a, vic_bg
    ld y, 0

    call clear_screen

    copy game_state_title_screen, dispatch_game_state

    copy word 0, pos
    with interrupts off {
        copy cinv, save_cinv
        copy our_cinv, cinv
    }

    repeat { } forever
}