Andrew Kesterson
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You were right that this was still everywhere. The two `.bas` files carried their workarounds as present-tense statements about the interpreter -- "a name first created inside a GOSUB costs a value slot that is never handed back", "writing PAST the terminator of a short row draws nothing at all", "SSHAPE and GSHAPE ignore the subscript on a string array", "a FOR inside a BEGIN block does not survive the RETURN" -- and every one of those is now false. A comment that lies is worse than no comment, and these were the first thing anybody opening the files would read. **The characters game takes the geometry fix.** `CW# = 16` becomes `CW# = RGR(3)`, and the grid comes from `RWINDOW`, so the game fits whatever window and font the host gives it. That was the one thing in the listing that would break on a different font, and `RGR(3)` and `RWINDOW` were added to the interpreter because of it -- leaving the constant in place while Chapter 17 teaches the function was the inconsistency worth closing. `RGR(1)` still comes first so a build with no graphics device refuses by naming the device that is missing. Everything else in both listings keeps its shape and says why. Declaring every name up front, guarding loops with `GOTO`, six scalars for six brick stamps: none is forced any more and none costs anything, so they stay, with the comments marking which rules stand and which are history. The sprites header's five traps are marked FIXED where they are fixed. The chapters follow: Chapter 17 Step 2 no longer says "the listing still has `CW# = 16`", and Chapter 18's trap section is "five things that did not do what they looked like" with the two that still stand named up front rather than left to be counted. Verified: Chapter 17 Step 2's block is once again verbatim from the listing, so every quoted fragment in both chapters matches its source with no exceptions; both games run 40 seconds on the SDL frontend with no error line; both suites green in both configurations; `docs_examples` and `docs_screenshots --check` pass. Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
100 lines
5.1 KiB
Markdown
100 lines
5.1 KiB
Markdown
# Breakout, with artwork
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Breakout, written entirely in BASIC for the AKGL BASIC interpreter, using downloaded CC0
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sprite artwork for the paddles, the balls and the powerup gems. The bricks, the HUD and
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the lettering are drawn, captured with `SSHAPE` and installed as sprites — because a
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sprite is the one thing this interpreter puts on the screen for nothing. The text layer
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owns every row of the window unless a program takes some back with `WINDOW`, and even
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then a drawing has to be re-issued every frame; a sprite is drawn from state the
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interpreter keeps.
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```sh
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../../../build-akgl/basic breakout.bas
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```
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It needs the SDL build. Without a graphics device the first `SPRSAV` refuses by name and
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the program stops there, which is the right thing for it to do.
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| Key | Does |
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|---|---|
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| left / right | move the paddle |
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| space | start a game, launch the ball, release a stuck ball |
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| P | pause |
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| S | sound on and off |
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| Q or escape | quit |
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Three lives, six rows of bricks worth 60 down to 10 points a row, and a field that cycles
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six rows, then five, then four while the ball gets faster every level up to a ceiling. A
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gem is worth 50 on top of whatever it does.
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## The powerups
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A broken brick drops a gem about one time in seven, and only ever one at a time. Catch it
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with the paddle. The colour of the gem is what tells you which it is; the banner that
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flashes over the field names it as well.
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| Gem | Name | Does | For |
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|---|---|---|---|
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| red | EXPAND | doubles the paddle's width | 20 seconds |
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| yellow | MULTI | throws two more balls off the one in play | until they are lost |
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| green | SLOW | drops the ball's speed to about two thirds | 16 seconds |
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| blue | STICKY | the ball sticks where it lands; space fires it | 18 seconds |
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| purple | CATCH | a second bar appears higher up the field | 24 seconds |
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The second bar **mirrors** the paddle rather than following it, so it covers the side you
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just left. A second bar directly above the first is worth nothing; a mirrored one turns a
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dive across the field into a save at both ends.
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## How it works, and how to write your own
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**[Chapter 18 of the guide](../../../docs/18-tutorial-breakout-artwork.md)** builds this
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program a step at a time: budgeting the eight sprite slots, capturing a drawing into one,
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finding the host's frame boundary with `TI#`, moving everything that is not drawing out of
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the deadline, the stroke font, and the five things in this dialect that do not do what
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they look like.
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[Chapter 17](../../../docs/17-tutorial-breakout.md) does the same for
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[`../characters`](../characters), which builds the same game out of the text grid and two
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`DATA` sprites — a completely different program, and the shorter one to read first.
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## Where the artwork came from
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Kenney's [Puzzle Pack 1](https://kenney.nl/assets/puzzle-pack-1), released under
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[CC0](http://creativecommons.org/publicdomain/zero/1.0/). The files in `art/` are the
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pack's own `PNG/Default/` versions, unmodified, with the pack's licence file beside them.
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`art/PROVENANCE.md` says which file is used for what and why the double-size set is not.
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Crediting Kenney is not required by CC0. It is here because it should be.
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## What is not in it
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Named honestly rather than left to be discovered:
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- **No music under the game**, only event sounds and two four-note stings. There is room in
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the third voice for it; there was not much room anywhere else when it was written. 121 of
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the interpreter's 128 variables are spoken for and the label table is at 61 of 64 —
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several of them spent working around defects that have since been fixed.
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- **One gem at a time.** There is one sprite slot for it. A brick broken while a gem is
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falling drops nothing.
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- **Sticky and multiball share one offset.** Two balls stuck to the paddle at once sit on
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top of each other. It is rare enough that fixing it would cost a variable I do not have.
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- **The score lags a frame behind the bricks.** Only one capture happens per frame and the
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field goes first, so a brick disappears one frame before the score that counts it. At
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thirty frames a second nobody can see it, and it is a deliberate trade rather than an
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oversight.
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- **No high score on disk.** There is no disk.
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The eight interpreter defects this game turned up are filed in `TODO.md` §9, each with a
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reduction that fits on a screen and the file and line of the cause. **Six are now fixed**
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— the leaking `DEF` call, the skipped block that broke its caller's `RETURN`, the ignored
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subscript on `SSHAPE`, `GRAPHIC CLR`, a negative `DATA` item, and half of the invisible
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drawing. The two that stand are the left-operand arithmetic rule, which turned out to be a
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decision rather than a defect and is now documented as one, and the 256-line batch tear,
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which belongs to the host.
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**The listing's code is unchanged**, and deliberately: it is what a program written
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against those constraints looks like, and none of the workarounds costs anything now that
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they are not needed. Six separate scalars for six brick stamps, and loops guarded by
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`GOTO` rather than wrapped in a block, are both still what the file does. Its comments say
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which of the five traps stand and which are marked FIXED.
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