Andrew Kesterson
91fadf032b
Eleven of the thirteen defects these two games found are fixed, and the chapters that taught around them said things that are no longer true. Chapter 17: the drawing verbs are no longer invisible, they are covered by a text layer that `WINDOW` can now shrink; the cell size is `RGR(3)` and the grid is `RWINDOW`, not a hand-measured constant; a character written past a short row's end lands. Chapter 18: traps 3 and 4 -- the skipped block that broke its caller's `RETURN`, and `SSHAPE` ignoring a subscript -- become history rather than warnings, and Step 3 no longer claims a sprite is the *only* way to put a picture up, only the one that costs nothing. **Neither `.bas` listing changes, and both READMEs now say why.** The character game still writes `CW# = 16` and the artwork game still keeps six brick stamps in six scalars. What those listings are worth is being what a program written against those constraints looks like, with comments explaining what each one was avoiding -- rewriting them to pretend the problems never existed would throw that away. So Chapter 17 Step 2 shows the `RGR(3)`/`RWINDOW` form and says plainly that the listing beside it does not use it. That is the one place in either chapter where a quoted fragment is not verbatim from the game. Also: the closing pointers now say which entries are struck and which stand, and the budgets table in Chapter 18 notes that several of those budgets were tighter when the game was written. TODO.md section 9 item 3 is updated rather than struck: the `WINDOW` half is fixed, the default text area owning the whole window is not, and whether that default is right is a question rather than a defect. Verified against the fixed interpreter: both games run 45 seconds on the SDL frontend with no error line and the score climbing; both suites are green in both configurations; `docs_examples` passes and `docs_screenshots --check` re-renders all thirteen figures byte-identically; coverage is 95.0% of lines against the 90 gate, with src/variable.c at 100%; and every other quoted fragment still appears verbatim in the listing it came from. Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
4.8 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 was not much room anywhere else when it was written. 121 of the interpreter's 128 variables are spoken for and the label table is at 61 of 64 — several of them spent working around defects that have since been fixed.
- 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 and the file and line of the cause. Six are now fixed
— the leaking DEF call, the skipped block that broke its caller's RETURN, the ignored
subscript on SSHAPE, GRAPHIC CLR, a negative DATA item, and half of the invisible
drawing. The two that stand are the left-operand arithmetic rule, which turned out to be a
decision rather than a defect and is now documented as one, and the 256-line batch tear,
which belongs to the host.
The listing is unchanged, and deliberately: it is what a program written against those constraints looks like, and its comments explain what it was working around. Six separate scalars for six brick stamps is no longer necessary, and it is still what the file does.