# 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 — `WINDOW` moves the text layer to two rows at the bottom, and
everything the program draws then stays on the screen without being redrawn or captured.

The bricks are also **collidable without being sprites**: `SOLID` registers a rectangle
the interpreter collides against, so sixty of them cost none of the eight slots.

```sh
../../../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](../../../docs/18-tutorial-breakout-artwork.md)** builds this
program step by step: loading artwork, budgeting the eight sprite slots, taking the text
layer out of the way so a drawing can be seen, stamping the brick field, registering the
bricks as collision geometry, the stroke font, the bounce without a square root, and the
gems.

[Chapter 17](../../../docs/17-tutorial-breakout.md) does the same for
[`../characters`](../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](https://kenney.nl/assets/puzzle-pack-1), released under
[CC0](http://creativecommons.org/publicdomain/zero/1.0/). 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. The
  conversion gave some of that room back — the variable table is under the 128 ceiling with
  a handful to spare and the label table is at 57 of 64, where it was at 61.
- **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.
- **No high score on disk.** There is no disk.
- **No attract mode**, unlike `../characters`. It sits on the title screen until somebody
  presses space, which also means it cannot test itself unattended the way that one can.

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 has since been converted**, and its header records what went. It used to
spend two of its eight sprites on the screen itself — an `SSHAPE` of the HUD strip and one
of the whole play field, because a drawing lasted a single frame and a sprite was the only
thing redrawn for nothing. A drawing persists now, so both slots are free, the `PACE`
routine that hunted for a frame boundary is gone with the captures it protected, and the
flattened live list that made a full-field redraw cheap is gone with the redraw itself: a
broken brick is erased in place.

What has *not* changed is the shape of the workarounds that no longer cost anything — six
separate scalars for six brick stamps, loops guarded by `GOTO` rather than wrapped in a
block. Its comments say which of the five traps still stand and which are marked FIXED.
