Andrew Kesterson
9e43acc0b0
`HITTEST`, `XBRICK` and `YBRICK` are gone -- about forty lines that divided pixels by cell sizes to recover a grid index, tested the ball's leading edge rather than its box, and could miss a brick clipped at the corner by seven pixels' worth of ball. In their place: sixty `SOLID` rectangles registered as the wall is built, `COLLISION 2, BRICKHIT`, and a fifteen-line handler. The handler reads better than what it replaces because it asks rather than derives. `RCOLLISION(1, 1)` is which brick -- the id is the array index plus one, so nothing is looked up. Fields 2, 3 and 4 are the way out and how far, so the ball is pushed exactly clear instead of being restored to a remembered `OX#`/`OY#`. Field 7 is which axis to reverse, which `TESTCELL` in the other game computes by hand from an overlap rectangle. `MOVEBAL` loses its two brick calls and its position backup. `KILLBR` retires the rectangle in the same breath as clearing the array element, so the next frame cannot hit a brick that is no longer drawn. **A latent defect in the target prescan had to be fixed first, and `RCOLLISION` is the first name in the language to reach it.** `src/renumber.c` walks a line character by character looking for `GOTO`, `GOSUB`, `COLLISION` and the rest, and checked only the character *after* a match -- so `RCOLLISION(1, 1)` found `COLLISION` at its second character, read the `(1,` that followed as a handler line number, and refused the whole program with "branch to line 1, which the program did not number", naming a line that contains no branch at all. It now requires a word boundary on both sides. The comment there was already right that the trailing check protects `GOTOX#`; nothing protected `XGOTO#`. `tests/unnumbered.c` covers all three shapes and TODO.md section 6 item 42 records it. The game runs ninety seconds headless with no error line and the attract mode scores 1320, so bricks are being found and broken through the new path. Chapter 17 is not updated yet -- that is the other half of section 6 item 39, and it is a bigger edit than this one. Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01EwxGB6TdoVvZ11KQQME9cL
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 the first RGR refuses
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 in
fifteen steps you can type in one at a time, starting from an empty file: measuring the
screen, declaring every name before anything uses it, making the two sprites out of DATA,
building a text row whole, the main loop, the ball, the bounce, and the attract mode. 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 used to be a constant.
CW#andCH#were 16, measured by hand against the bundled C64_Pro_Mono at 16 points, because BASIC had no way to ask — and it was the one thing here that would break on a different font.RGR(3),RGR(4)andRWINDOWwere added to the interpreter because of this listing, and it uses them now, so the game fits whatever window and font the host gives it. - 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 and §9, each with a
reduction that fits on a screen. Most are now fixed — the value pool that killed the first
version after twenty-five seconds, the unreachable WINDOW, the character written past a
short row — and the entries are struck rather than deleted, because the reduction is worth
keeping.
The listing takes the geometry fix and leaves the rest of its shape alone. Measuring
the cell instead of assuming it makes the game strictly better, so it does. Declaring
every name up front and looping with GOTO are no longer forced by anything, and are
still what the file does — its comments now say which rules stand and which are history.
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.