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>
4.1 KiB
Breakout, with artwork
Breakout, written entirely in BASIC for the AKGL BASIC interpreter, using downloaded CC0
sprite artwork for the paddles, the balls and the powerup gems. The bricks, the HUD and
the lettering are drawn, captured with SSHAPE and installed as sprites — which is the
only way a program in this interpreter can put a picture on the screen.
../../../build-akgl/basic breakout.bas
It needs the SDL build. Without a graphics device the first SPRSAV refuses by name and
the program stops there, which is the right thing for it to do.
| Key | Does |
|---|---|
| left / right | move the paddle |
| space | start a game, launch the ball, release a stuck ball |
| P | pause |
| S | sound on and off |
| Q or escape | quit |
Three lives, six rows of bricks worth 60 down to 10 points a row, and a field that cycles six rows, then five, then four while the ball gets faster every level up to a ceiling. A gem is worth 50 on top of whatever it does.
The powerups
A broken brick drops a gem about one time in seven, and only ever one at a time. Catch it with the paddle. The colour of the gem is what tells you which it is; the banner that flashes over the field names it as well.
| Gem | Name | Does | For |
|---|---|---|---|
| red | EXPAND | doubles the paddle's width | 20 seconds |
| yellow | MULTI | throws two more balls off the one in play | until they are lost |
| green | SLOW | drops the ball's speed to about two thirds | 16 seconds |
| blue | STICKY | the ball sticks where it lands; space fires it | 18 seconds |
| purple | CATCH | a second bar appears higher up the field | 24 seconds |
The second bar mirrors the paddle rather than following it, so it covers the side you just left. A second bar directly above the first is worth nothing; a mirrored one turns a dive across the field into a save at both ends.
How it works, and how to write your own
Chapter 18 of the guide builds this
program a step at a time: budgeting the eight sprite slots, capturing a drawing into one,
finding the host's frame boundary with TI#, moving everything that is not drawing out of
the deadline, the stroke font, and the five things in this dialect that do not do what
they look like.
Chapter 17 does the same for
../characters, which builds the same game out of the text grid and two
DATA sprites — a completely different program, and the shorter one to read first.
Where the artwork came from
Kenney's Puzzle Pack 1, released under
CC0. The files in art/ are the
pack's own PNG/Default/ versions, unmodified, with the pack's licence file beside them.
art/PROVENANCE.md says which file is used for what and why the double-size set is not.
Crediting Kenney is not required by CC0. It is here because it should be.
What is not in it
Named honestly rather than left to be discovered:
- No music under the game, only event sounds and two four-note stings. There is room in the third voice for it; there is not much room anywhere else. 121 of the interpreter's 128 variables are spoken for, four more are the ones it makes itself, and the label table is at 61 of 64.
- One gem at a time. There is one sprite slot for it. A brick broken while a gem is falling drops nothing.
- Sticky and multiball share one offset. Two balls stuck to the paddle at once sit on top of each other. It is rare enough that fixing it would cost a variable I do not have.
- The score lags a frame behind the bricks. Only one capture happens per frame and the field goes first, so a brick disappears one frame before the score that counts it. At thirty frames a second nobody can see it, and it is a deliberate trade rather than an oversight.
- No high score on disk. There is no disk.
The eight interpreter defects this game turned up are filed in TODO.md §9, each with a
reduction that fits on a screen, the file and line of the cause, and what a fix would
touch.