Andrew Kesterson
f005b88980
`SPRHIT n, kind [,x1, y1, x2, y2]` gives a sprite a collision shape: a box, a circle inscribed in it, or a capsule. `RSPHIT(n, f)` reads it back in SPRHIT's own argument order, the way RSPRITE and RSPPOS already do, and needs no device because it answers from interpreter state. The rectangle is two corners measured from the sprite's top-left, in device pixels -- the same `x1, y1, x2, y2` that `BOX` and `SSHAPE` take. A dialect with two spellings for a rectangle is one nobody can write from memory. Omit it and the shape fits whatever the picture turned out to be, which is what a sprite loaded from a file needs: `SPRSAV "ship.png", 1` takes the image's own size and the program never learns what that was. **A sprite nobody has shaped collides with its whole frame, expansion bits included, exactly as before.** That is a promise rather than a convenience, and it has its own test: the same two sprites in the same two places, once with no SPRHIT and once with a four-pixel box, reporting a collision and then not. Named SPRHIT rather than SPRSHAPE because "shape" already means "a region SSHAPE saved" in this dialect, in this very chapter -- `SPRSAV A$, 1` takes one -- and a reader who typed `SPRSHAPE A$, 1` would have had every reason to. Both names, and RSPHIT, were grepped against every label in docs/, examples/ and both corpora first: a bare word is a label here, so a verb and a label share one namespace and taking a name a checked-in listing already uses would break it silently. `SPRHIT n, 0` takes a sprite out of collision while leaving it on the screen -- the ghost, the flashing invulnerable player, the pickup already taken. Hiding it with `SPRITE n, 0` stops it colliding too, and is what you want when it should not be seen either. The circle answers the complaint chapter 8 already ships a figure of. That figure shows two discs whose *boxes* touch at a corner while the artwork is nowhere near, and `BUMP(1)` reporting a collision; two `SPRHIT n, 2` and it stops. The test asserts both halves so the figure's caption stays true. `tests/verbs_table.c` caught RSPHIT filed after RSPPOS rather than before it, which is the sorted-table test doing exactly the job it exists for. Docs: a new section in chapter 8, rows in the verb and function references in alphabetical order, and chapter 13's "collision is by bounding box" becomes "collision is by shape" with the addition named. 111 with akgl, 110 without, and the artwork breakout still runs clean. Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01EwxGB6TdoVvZ11KQQME9cL
The akbasic guide
akbasic is a BASIC interpreter in the style of Commodore BASIC 7.0 — the dialect the C128 shipped with — and Dartmouth BASIC. It runs programs from a file or from an interactive prompt, and it is also a C library you can link into a game so that players can script it.
These chapters follow the shape of the C128 Programmer's Reference Guide: the language first, then each hardware area, then the reference sections. If you know BASIC 7.0 you can skip to Chapter 13, which is the list of everything that behaves differently here and why. Chapter 14 is the odd one out: it is about the interpreter rather than the language, for anyone embedding it, debugging it or changing it.
Chapters 17 and 18 are tutorials rather than reference: they build one complete game twice, two different ways, in numbered steps you can type in one at a time. Start with 17 — it needs nothing but the earlier chapters, and 18 assumes it.
Chapters
| 1. Introduction | What akbasic is, what it is not, and how to build it |
| 2. Getting started | The prompt, your first program, saving and loading |
| 3. The language | Variables, types, arrays, operators, expressions |
| 4. Control flow | IF, FOR, DO, GOSUB, labels, ON, error trapping |
| 5. Strings and formatting | String functions, PRINT USING, PUDEF |
| 6. Graphics | GRAPHIC, DRAW, BOX, CIRCLE, PAINT, shapes |
| 7. Sound | SOUND, PLAY, ENVELOPE, VOL, TEMPO |
| 8. Sprites | SPRITE, SPRSAV, MOVSPR, collision |
| 9. Files and disk | Channels, DOPEN, program storage |
| 10. Embedding | Driving the interpreter from C |
| 11. Verb reference | Every statement, alphabetically |
| 12. Function reference | Every function, alphabetically |
| 13. Differences from BASIC 7.0 | What a C128 programmer needs to know |
| 14. Architecture | How the interpreter is put together, how to debug it, how to change it |
| 15. Error codes | Appendix: every value ER# can hold and every error line the interpreter prints |
| 16. Structures | TYPE, records, strict pointers, and sharing a C struct with an embedding host |
| 17. Tutorial: Breakout | Build a whole game out of the text grid and two DATA sprites, in sixteen steps |
| 18. Tutorial: Breakout with artwork | Build it again out of loaded artwork, powerups and a drawn colour HUD, in thirteen |
The shortest possible start
$ cmake -S . -B build && cmake --build build
$ ./build/basic
10 FOR I# = 1 TO 5
20 PRINT "HELLO " + I#
30 NEXT I#
RUN
HELLO 1
HELLO 2
HELLO 3
HELLO 4
HELLO 5
READY
Two things in that program are not Commodore BASIC and will catch you out
immediately: variables carry a type suffix (I# is an integer) and +
concatenates a string with a number. Chapter 3 explains both.
Every example in these chapters is executed by the test suite and its output
compared byte for byte — see MAINTENANCE.md if you are editing them.