akbasic/examples/breakout/characters/breakout.bas

REM ####################################################################
REM BREAKOUT
REM
REM One hundred percent BASIC, for the AKGL BASIC interpreter.
REM   ../akbasic/build-akgl/basic breakout.bas
REM
REM The ball and the paddle are sprites, defined from DATA in this listing.
REM The bricks, the HUD and the messages are characters in the text grid.
REM Nothing here loads an asset and nothing here uses DRAW, BOX or CIRCLE:
REM the drawing verbs do not survive a frame in this interpreter, while the
REM text grid and the sprites are both redrawn from persistent state every
REM frame. See README.md for the whole list of things that shaped this.
REM
REM Three rules this listing never breaks, each one earned the hard way:
REM   * A row of text is written whole, from column 0. CHAR terminates the
REM     row where it stops, so writing at column N erases N+1 onwards.
REM   * Mixed + and - are parenthesised. This parser reads a - b + c as
REM     a - (b + c), and matches only ONE unparenthesised AND or OR.
REM   * The main loop is a GOTO loop. Every loop and every GOSUB takes one
REM     of 32 scopes, and a state change jumping out of a DO would leak one
REM     every time; thirty-two lives later the program stops.
REM
REM Two more rules were true when this was written and are not any more.
REM They are recorded because the shape of the listing is still theirs:
REM   * Every name is created once, in the pool block below. A name first
REM     created inside a GOSUB or a FOR used to cost a value slot that was
REM     never handed back, out of 4096 for the whole run, and this game died
REM     after twenty-five seconds because of it. A scalar is free now; only
REM     the DIMs below still have to be up here. TODO.md section 6 item 30.
REM   * Writing PAST the terminator of a short row used to draw nothing at
REM     all. The gap is padded with spaces now. TODO.md section 6 item 32.
REM
REM Written by Claude Opus (1M)
REM ####################################################################

LABEL SETUP
SCNCLR

REM --- geometry -------------------------------------------------------
REM Nothing here is assumed. RGR(1) and RGR(2) are the window in pixels,
REM RGR(3) and RGR(4) are one character cell, and RWINDOW gives the text
REM grid in columns and rows -- so the game fits whatever window the host
REM opened and whatever font it loaded. Everything below is derived from
REM these six, including the ball's speed relative to the wall.
REM
REM The first version of this file had CW# = 16 and CH# = 16 written out,
REM measured by hand against the bundled C64_Pro_Mono at 16 points, because
REM there was no way to ask -- and that was the one thing in the listing
REM that would break on a different font. RGR(3) and RWINDOW were added to
REM the interpreter because of it.
SCW# = RGR(1)
SCH# = RGR(2)
CW# = RGR(3)
CH# = RGR(4)
COLS# = RWINDOW(1)
ROWS# = RWINDOW(0)

REM --- the brick wall, in cells ---------------------------------------
BRW# = 4
BCOLS# = 10
BROWS# = 6
BTOP# = 4
BLEFT# = (COLS# - (BRW# * BCOLS#)) / 2

REM --- the play area, in pixels ---------------------------------------
TOPY# = 2 * CH#
MAXX# = SCW# - 8
PW# = 144
PY# = 528
LOSEY# = PY# + 32
MSGROW# = 35
TITROW# = 20
PSPD# = 10

REM --- pools ----------------------------------------------------------
REM Every name in the program is created HERE.
REM
REM One reason still stands. A GOSUB gets its own scope: assignment walks up
REM the chain and finds an outer variable, but a name first seen inside a
REM subroutine is created in the subroutine and dies at RETURN -- so HIT#
REM and BI# would mean nothing to the caller if they were not already out
REM here, and HITTEST would answer into two variables nobody can read.
REM
REM The other has been fixed. A scalar used to cost a value slot for good --
REM the pool is a bump allocator with no free, and recycling a variable took
REM fresh slots, so 4096 creations ended the run whenever they happened. A
REM scalar now lives in the variable itself and costs the pool nothing; only
REM the DIMs still spend, which is why they are the part that has to be up
REM here. The rest of this block is habit, and harmless.
DIM BR#(60)
DIM SB#(63)
DIM SP#(63)
DIM LAY$(6)
DIM BSG$(6)

SCORE# = 0
HIGH# = 0
LIVES# = 3
LEVEL# = 1
LEFTN# = 0
BSPD# = 4
STATE# = 0
DEMO# = 0
PAUSED# = 0
HELD# = 0
PDIR# = 0
PDEC# = 0
PX# = 0
BX# = 0
BY# = 0
BVX# = 0
BVY# = 0
OX# = 0
OY# = 0
K# = 0
HIT# = 0
SX# = 0
SY# = 0
A# = 0
D% = 0.0
M# = 0
PVX# = 0
DOFF# = 0
STALL# = 0
NUDGE# = 0
BI# = 0
BR2# = 0
RB# = 0
CB# = 0
RC# = 0
CC2# = 0
TX# = 0
TY# = 0
PTS# = 0
V# = 0
L# = 0
C2# = 0
D# = 0
M# = 0
X2# = 0
X3# = 0
Z# = 0
BB# = 0
RX# = 0
N# = 0
MROW# = 0
RMAX# = 2
RND# = 0
SND# = 0
P$ = ""
H$ = ""
S$ = ""
T$ = ""
MSG$ = ""
BSEG$ = ""
FRAME$ = ""
I# = 0
R# = 0
R2# = 0
C# = 0
CC# = 0
KI# = 0
T# = 0

REM Brick faces, one per wall row. CHAR ignores its colour argument --
REM the sink draws in one colour -- so the rows are told apart by shape.
BSG$(0) = "[##]"
BSG$(1) = "[##]"
BSG$(2) = "[==]"
BSG$(3) = "[==]"
BSG$(4) = "[--]"
BSG$(5) = "[--]"

REM --- the seed -------------------------------------------------------
REM There is no RND in this dialect. TI# is jiffies off the host's clock
REM and is host uptime rather than zero-based, which makes it a fine seed.
SEED# = TI#

REM The ceiling, drawn once. TOPY# is the bottom edge of this row, so the
REM ball turns against something the player can see rather than against an
REM invisible line two rows down from the top of the window.
FRAME$ = "=" * COLS#
CHAR 1, 0, 1, FRAME$

GOSUB MKSPR
GOSUB SNDPROBE
COLLISION 2, BRICKHIT
GOTO TITLE

REM ####################################################################
REM  SPRITES
REM ####################################################################

LABEL MKSPR
FOR I# = 0 TO 62
  READ SB#(I#)
NEXT I#
FOR I# = 0 TO 62
  READ SP#(I#)
NEXT I#
SPRSAV SB#, 1
SPRITE 1, 1, 2
SPRSAV SP#, 2
SPRSAV SP#, 3
SPRSAV SP#, 4
SPRITE 2, 1, 15, 0, 1, 0
SPRITE 3, 1, 15, 0, 1, 0
SPRITE 4, 1, 15, 0, 1, 0
RETURN

REM ####################################################################
REM  SOUND
REM
REM SOUND refuses on a machine with no audio device, and an untrapped
REM refusal would end the game. Ask once, remember the answer, and never
REM ask again -- the game is silent where there is nothing to play on.
REM ####################################################################

LABEL SNDPROBE
SND# = 1
TRAP NOAUDIO
SOUND 1, 2000, 1
TRAP
RETURN

LABEL NOAUDIO
SND# = 0
RESUME NEXT

LABEL BEEPB
IF SND# = 1 THEN SOUND 1, 12000, 2
RETURN

LABEL BEEPP
IF SND# = 1 THEN SOUND 2, 6000, 3
RETURN

LABEL BEEPW
IF SND# = 1 THEN SOUND 3, 9000, 1
RETURN

LABEL BEEPL
IF SND# = 1 THEN SOUND 1, 1500, 20
RETURN

REM ####################################################################
REM  TITLE AND ATTRACT MODE
REM
REM The title screen plays itself. It is also how this game gets tested
REM without a human at the keyboard.
REM ####################################################################

LABEL TITLE
DEMO# = 1
SCORE# = 0
LIVES# = 3
LEVEL# = 1
BSPD# = 4
PAUSED# = 0
GOSUB LOADLAY
GOSUB BUILDW
GOSUB DRAWW
GOSUB DRAWHUD
GOSUB TITTEXT
GOSUB SERVE
STATE# = 0
GOTO TICK

LABEL TITTEXT
MROW# = TITROW#
MSG$ = "B R E A K O U T"
GOSUB SHOWAT
MROW# = TITROW# + 2
MSG$ = "PRESS SPACE TO PLAY"
GOSUB SHOWAT
MROW# = TITROW# + 4
MSG$ = "LEFT AND RIGHT MOVE   P PAUSES   Q QUITS"
GOSUB SHOWAT
MROW# = TITROW# + 6
MSG$ = "ATTRACT MODE"
GOSUB SHOWAT
RETURN

LABEL CLRTIT
MROW# = TITROW#
GOSUB CLRAT
MROW# = TITROW# + 2
GOSUB CLRAT
MROW# = TITROW# + 4
GOSUB CLRAT
MROW# = TITROW# + 6
GOSUB CLRAT
RETURN

REM ####################################################################
REM  GAME AND LEVEL SETUP
REM ####################################################################

LABEL NEWGAME
DEMO# = 0
SCORE# = 0
LIVES# = 3
LEVEL# = 1
BSPD# = 4
PAUSED# = 0
GOSUB CLRTIT
GOSUB NEWLEV
STATE# = 0
GOTO TICK

LABEL NEWLEV
GOSUB LOADLAY
GOSUB BUILDW
GOSUB DRAWW
GOSUB DRAWHUD
GOSUB SERVE
MSG$ = "PRESS SPACE TO LAUNCH"
GOSUB SHOWMSG
RETURN

REM Three layouts, then round again with a faster ball. RESTORE takes a
REM label -- it wants a line and a label evaluates to one -- so a layout is
REM simply a named place in the DATA stream.
LABEL LOADLAY
N# = MOD((LEVEL# - 1), 3)
IF N# = 0 THEN RESTORE LAY1
IF N# = 1 THEN RESTORE LAY2
IF N# = 2 THEN RESTORE LAY3
FOR R# = 0 TO 5
  READ LAY$(R#)
NEXT R#
RETURN

LABEL BUILDW
LEFTN# = 0
FOR R# = 0 TO 5
  S$ = LAY$(R#)
  GOSUB BUILDR
NEXT R#
RETURN

REM One wall row. Each brick is registered with SOLID as well as recorded in
REM BR#(), so the interpreter can answer "did the ball hit a brick" and, more
REM usefully, "which one and which way is out". The id is the array index plus
REM one, so nothing has to be looked up on the way back.
LABEL BUILDR
FOR C# = 0 TO 9
  T$ = MID(S$, C#, 1)
  I# = (R# * BCOLS#) + C#
  BR#(I#) = 0
  IF T$ = "1" THEN BR#(I#) = 1
  IF T$ = "1" THEN LEFTN# = LEFTN# + 1
  SX# = (BLEFT# + (C# * BRW#)) * CW#
  SY# = (BTOP# + R#) * CH#
  IF T$ = "1" THEN SOLID I# + 1, SX#, SY#, SX# + (BRW# * CW#), SY# + CH#
  IF T$ = "0" THEN SOLID I# + 1
NEXT C#
RETURN

LABEL DRAWW
FOR R# = 0 TO 5
  BR2# = R#
  GOSUB DRAWBR
NEXT R#
RETURN

REM One brick row, rebuilt whole and written in a single CHAR. Anything
REM else would truncate the row at the first character it wrote.
LABEL DRAWBR
S$ = ""
IF BLEFT# > 0 THEN S$ = " " * BLEFT#
BSEG$ = BSG$(BR2#)
FOR CC# = 0 TO 9
  I# = (BR2# * BCOLS#) + CC#
  IF BR#(I#) = 1 THEN S$ = S$ + BSEG$
  IF BR#(I#) = 0 THEN S$ = S$ + "    "
NEXT CC#
R2# = BTOP# + BR2#
CHAR 1, 0, R2#, S$
RETURN

REM Put the ball back on the paddle, pointing up, left or right at random.
LABEL SERVE
PX# = (SCW# - PW#) / 2
HELD# = 1
IF DEMO# = 1 THEN HELD# = 0
BX# = PX# + ((PW# / 2) - 4)
BY# = PY# - 10
RMAX# = 2
GOSUB RANDOM
BVX# = BSPD#
IF RND# = 0 THEN BVX# = 0 - BSPD#
BVY# = 0 - BSPD#
PDEC# = 0
GOSUB SHOWSPR
RETURN

REM A linear congruential generator, because this dialect has no RND.
REM The multiply stays inside int64 for any seed under 2^31.
LABEL RANDOM
SEED# = MOD(((SEED# * 1103515245) + 12345), 2147483648)
RND# = MOD((SEED# / 65536), RMAX#)
RETURN

REM ####################################################################
REM  THE MAIN LOOP
REM
REM A GOTO loop rather than DO/LOOP on purpose: every loop and every
REM GOSUB pushes one of 32 scopes, and a state change that jumped out of
REM a DO would leak one every time. This loop pushes nothing.
REM ####################################################################

LABEL TICK
GOSUB READKEY
IF STATE# <> 0 THEN GOTO DISPATCH
IF PAUSED# = 1 THEN GOTO TICKEND
GOSUB MOVEPAD
IF HELD# = 1 THEN GOSUB HOLDBAL
IF HELD# = 0 THEN GOSUB MOVEBAL
GOSUB SHOWSPR
LABEL TICKEND
SLEEP 0.02
GOTO TICK

LABEL DISPATCH
IF STATE# = 1 THEN GOTO LOSTLIF
IF STATE# = 2 THEN GOTO LEVELUP
IF STATE# = 3 THEN GOTO BYE
IF STATE# = 5 THEN GOTO NEWGAME
STATE# = 0
GOTO TICK

REM ####################################################################
REM  INPUT
REM
REM GET is the only non-blocking read there is, and there is no key-up
REM event and no held-key state. What there IS is the host's own key
REM repeat, which arrives as ordinary key-down events about once per tick.
REM So a keystroke refills a countdown and the paddle coasts to a stop
REM when the repeats stop: held reads as held, tapped reads as a nudge.
REM ####################################################################

LABEL READKEY
FOR KI# = 1 TO 8
  GET K#
  IF K# <> 0 THEN GOSUB HANDKEY
NEXT KI#
RETURN

LABEL HANDKEY
IF K# = 1073741904 THEN PDIR# = 0 - 1
IF K# = 1073741904 THEN PDEC# = 12
IF K# = 1073741903 THEN PDIR# = 1
IF K# = 1073741903 THEN PDEC# = 12
IF K# = 32 THEN GOSUB KEYSPC
IF K# = 112 THEN GOSUB KEYPAU
IF K# = 113 THEN STATE# = 3
IF K# = 27 THEN STATE# = 3
RETURN

LABEL KEYSPC
IF DEMO# = 1 THEN STATE# = 5
IF DEMO# = 1 THEN RETURN
IF HELD# = 0 THEN RETURN
HELD# = 0
GOSUB CLRMSG
RETURN

LABEL KEYPAU
IF DEMO# = 1 THEN RETURN
PAUSED# = 1 - PAUSED#
IF PAUSED# = 1 THEN MSG$ = "PAUSED"
IF PAUSED# = 1 THEN GOSUB SHOWMSG
IF PAUSED# = 0 THEN GOSUB CLRMSG
RETURN

REM ####################################################################
REM  THE PADDLE
REM ####################################################################

LABEL MOVEPAD
IF DEMO# = 1 THEN GOSUB DEMOPAD
IF DEMO# = 1 THEN GOTO PADCLMP
IF PDEC# < 1 THEN GOTO PADCLMP
PDEC# = PDEC# - 1
PX# = PX# + (PDIR# * PSPD#)
LABEL PADCLMP
IF PX# < 0 THEN PX# = 0
M# = SCW# - PW#
IF PX# > M# THEN PX# = M#
RETURN

LABEL DEMOPAD
TX# = (BX# + 4) - (PW# / 2)
TX# = TX# + DOFF#
D# = TX# - PX#
IF D# > PSPD# THEN D# = PSPD#
M# = 0 - PSPD#
IF D# < M# THEN D# = M#
PX# = PX# + D#
RETURN

LABEL HOLDBAL
BX# = PX# + ((PW# / 2) - 4)
BY# = PY# - 10
RETURN

REM ####################################################################
REM  THE BALL
REM
REM X first and then Y, each move tested on its own, so a ball arriving
REM at the corner of a brick reverses one axis rather than both.
REM ####################################################################

REM Bricks are not tested here any more. COLLISION 2 fires when the ball meets
REM a SOLID rectangle and BRICKHIT does the rest, which is why there is no
REM OX#/OY# backup: the handler pushes the ball out along the contact normal
REM rather than restoring where it came from.
LABEL MOVEBAL
BX# = BX# + BVX#
IF BX# < 0 THEN GOSUB WALLL
IF BX# > MAXX# THEN GOSUB WALLR
BY# = BY# + BVY#
IF BY# < TOPY# THEN GOSUB WALLT
GOSUB PADHIT
IF BY# > LOSEY# THEN STATE# = 1
STALL# = STALL# + 1
IF STALL# > 500 THEN NUDGE# = 1
RETURN

LABEL WALLL
BX# = 0
BVX# = 0 - BVX#
GOSUB BEEPW
RETURN

LABEL WALLR
BX# = MAXX#
BVX# = 0 - BVX#
GOSUB BEEPW
RETURN

LABEL WALLT
BY# = TOPY#
BVY# = 0 - BVY#
GOSUB BEEPW
RETURN

REM ####################################################################
REM  BRICKS
REM
REM The whole of it. COLLISION 2 fires between source lines when the ball
REM overlaps a rectangle SOLID registered, and RCOLLISION says which one and
REM which way to go. This replaced HITTEST, XBRICK and YBRICK -- about forty
REM lines that divided pixels by cell sizes to recover a grid index, tested
REM the ball's leading edge rather than its box, and could miss a brick
REM clipped at the corner by seven pixels' worth of ball.
REM
REM Field 4 is how deep the overlap is and fields 2 and 3 are the way out, so
REM the two together put the ball exactly clear. The normal of a box against a
REM box is exactly -1, 0 or 1, which is why assigning the product into an
REM integer is safe here -- see chapter 13 on the left operand.
REM ####################################################################

LABEL BRICKHIT
M# = BUMP(2)
IF (M# AND 1) = 0 THEN RETURN
T# = RCOLLISION(1, 1)
IF T# < 1 THEN RETURN
IF BR#(T# - 1) = 0 THEN RETURN
D% = RCOLLISION(1, 4)
BX# = BX# + (RCOLLISION(1, 2) * D%)
BY# = BY# + (RCOLLISION(1, 3) * D%)
A# = RCOLLISION(1, 7)
IF A# = 1 THEN BVX# = 0 - BVX#
IF A# = 2 THEN BVY# = 0 - BVY#
BI# = T# - 1
BR2# = BI# / BCOLS#
GOSUB KILLBR
RETURN

LABEL KILLBR
BR#(BI#) = 0
SOLID BI# + 1
LEFTN# = LEFTN# - 1
STALL# = 0
PTS# = (BROWS# - BR2#) * 10
SCORE# = SCORE# + PTS#
IF DEMO# = 0 THEN GOSUB HISCORE
GOSUB DRAWBR
GOSUB DRAWHUD
GOSUB BEEPB
IF LEFTN# < 1 THEN STATE# = 2
RETURN

REM Paddle bounce. Five zones across the face, so where you catch it
REM decides where it goes -- the whole game, really.
LABEL PADHIT
IF BVY# < 1 THEN RETURN
BB# = BY# + 8
IF BB# < PY# THEN RETURN
IF BY# > (PY# + 10) THEN RETURN
RX# = PX# + PW#
IF (BX# + 8) < PX# THEN RETURN
IF BX# > RX# THEN RETURN
BY# = PY# - 8
BVY# = 0 - BSPD#
Z# = ((BX# + 4) - PX#) / (PW# / 5)
IF Z# < 0 THEN Z# = 0
IF Z# > 4 THEN Z# = 4
PVX# = BVX#
BVX# = (Z# - 2) * 3
IF BVX# <> 0 THEN GOTO PADAIM
REM Dead centre. Keep the direction it came in on and give it a shallow
REM angle: a ball with no sideways speed at all rises and falls down one
REM column for ever, which is how attract mode used to hang itself.
BVX# = 2
IF PVX# < 0 THEN BVX# = 0 - 2
LABEL PADAIM
IF NUDGE# = 1 THEN GOSUB UNSTICK
IF DEMO# = 1 THEN GOSUB DEMOAIM
GOSUB BEEPP
RETURN

REM Ten seconds without touching a brick means the ball has found an orbit
REM that misses the wall -- straight up and straight back down the same
REM empty column, usually. Give it a different angle, but do it HERE, on a
REM bounce the player is already watching, rather than in mid-flight where
REM it would look like the ball hit something that was not there.
LABEL UNSTICK
NUDGE# = 0
STALL# = 0
RMAX# = 4
GOSUB RANDOM
BVX# = (RND# * 3) - 6
IF BVX# = 0 THEN BVX# = 3
RETURN

REM Attract mode aims off-centre by a random amount, so the machine plays
REM like something with a hand on the paddle rather than a mirror.
LABEL DEMOAIM
RMAX# = 81
GOSUB RANDOM
DOFF# = RND# - 40
RETURN

REM ####################################################################
REM  DRAWING
REM ####################################################################

REM The sprite position is its top-left corner in device pixels, and the
REM paddle is three 48-wide segments laid end to end. Each coordinate is
REM worked out into a variable first: MOVSPR reads a leading sign as
REM "move by this much" rather than "move to here".
LABEL SHOWSPR
MOVSPR 1, BX#, BY#
MOVSPR 2, PX#, PY#