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 -------------------------------------------------------