Andrew Kesterson
cb0e2d0800
Two complete games in `examples/breakout/`, both 100% BASIC: `characters/` draws its wall in the text grid with two `DATA` sprites for the ball and paddle, and `sprites/` loads CC0 artwork and captures its whole screen with `SSHAPE`/`SPRSAV`. They take opposite shapes for reasons that are entirely this interpreter's, which is what the chapters are for. `docs/17-tutorial-breakout.md` and `docs/18-tutorial-breakout-artwork.md` build each one a step at a time, and end in a checklist of the rules a real program runs into: create every name before the loop starts, write a text row whole, loop with `GOTO` rather than `DO`, put the float on the left. Every trap is a runnable block with its own output rather than a claim -- the value pool dying at four thousand names, the skipped `BEGIN` block that breaks its caller's `RETURN`, `SSHAPE` ignoring a subscript, `READ`'s single cursor. Five figures, generated from the listings beside them by `docs_screenshots`, and a `breakout_art` setup so the ones that load artwork load the example's own. The character game's wall cannot be photographed -- the screenshot host omits the text layer on purpose -- so it is shown as compared output instead. `docs/07-sound.md` never said `SOUND`'s frequency is a SID register value rather than hertz, which both games depend on. It says so now, with the conversion from `src/audio_tables.c:84`. `TODO.md` gains the thirteen defects the two games turned up -- §6 items 30 to 33 and all of §9 -- each with a reduction that fits on a screen, the file and line of the cause, and what a fix would touch. Verified: `docs_examples` passes in both build configurations, `docs_screenshots --check` re-renders all thirteen figures and byte-compares them, the full 109-test suite passes in both builds, every quoted fragment was checked to appear verbatim in the listing it came from, and every relative link and anchor resolves. Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
3.7 KiB
Breakout
Breakout, written entirely in BASIC for the AKGL BASIC interpreter. The ball and the
paddle are sprites defined from DATA in the listing; the bricks, the HUD and the
messages are characters in the text grid.
../../../build-akgl/basic breakout.bas
It needs the SDL build. The stdio build has no graphics device, so RGR refuses on the
fourth line and the game stops there — which is exactly what it should do.
| Key | Does |
|---|---|
| left / right | move the paddle |
| space | start a game from the title screen, then launch the ball |
| P | pause |
| Q or escape | quit |
The title screen plays itself. Attract mode is a real feature and it is also how the game was tested without a hand on the keyboard.
Three lives, six rows of bricks worth 60 down to 10 points a row, three level layouts that repeat with a faster ball each time, and a high score that lasts as long as the process does.
How it works, and how to write your own
Chapter 17 of the guide builds this program a step at a time: what to make a sprite and what to make a character, why every name is declared before the game starts, how a text row has to be written whole, and the rest of the rules this listing never breaks. It is the tutorial; this is the finished thing.
Chapter 18 does the same for
../sprites, which builds the same game out of loaded artwork and comes out
a completely different program.
Known warts, this game's own
- The cell size is a constant.
CW#andCH#are 16, measured with the bundled C64_Pro_Mono at 16 points in the 800×600 window; the grid is 50×37. BASIC cannot ask —WINDOWknows, but the standalone frontend never offers it. Change the font or the window size and those two numbers have to change with them. - Every character the game draws also goes to stdout, because the frontend tees the text sink to the terminal. It made the whole game auditable from a log file during development and it is pure noise the rest of the time. Redirect it.
- Collision is against the cell the ball's leading edge is in, so a brick clipped at the very corner can be missed by up to seven pixels' worth of ball. Testing the centre instead was worse: the ball sank four pixels into a brick before it turned.
- There is a stall watchdog. Ten seconds without touching a brick and the ball gets a new angle — at the next paddle bounce, never in mid-air.
- The demo cannot lose, it re-serves. It also cannot be paused;
Pis ignored until a real game starts. - Sound is asked for once and then believed. On a machine with no audio device the game is silent rather than dead.
- No high score on disk. There is no disk in this interpreter.
The interpreter defects this game turned up are filed in TODO.md §6 item 30 and §9, each
with a reduction that fits on a screen.
How this was checked
- Parses clean under the stdio
basic(it then stops at the first graphics verb, as it should). - Attract mode run for 145 seconds and again for 110: no runtime error, score climbing throughout, 39 bricks in the second run.
- Level clear verified against a copy whose first layout is a single row:
LEVEL CLEARED, layout 2 loaded, ball speed up, play continues. - Input driven with
xdotoolagainst the real window: paddle moves and clamps at both edges, ball launches,Ppauses and unpauses, three lives drain toGAME OVER, space starts a new game,Qexits printing the final and high scores. - Every direction change logged for a whole run and read back: each one is a wall, a brick or the paddle. Nothing turns without a reason.