Andrew Kesterson
a9600c3fcc
The narrowphase has been producing a contact since it went in, and the interpreter was throwing it away. `RCOLLISION(n, f)` reports it: what was hit (a sprite or a `SOLID` rectangle), which one, the contact normal, the penetration depth, the contact point, and which axis to reverse. **The normal points out of the other thing and toward this one**, so a program moves along it by the depth and is exactly clear. That sign is the one assertion in the new test that could not be caught any other way -- both parties of a sprite-against-sprite hit get their own record, each pointing the way *that* sprite has to move, and sharing one would tell both to go the same direction, which is how two things end up stuck inside each other. **Field 7 is the one that deletes the most BASIC.** It is the minimum translation axis, computed from the normal in C, and it is there because doing it in BASIC means comparing two floats -- which is exactly where this dialect's left-operand rule catches people. `BALLBRICKS`/`TESTCELL` in the artwork breakout spend six lines computing an overlap rectangle and comparing its width to its height to get this number. The record is **sticky and deepest-wins**: replaced whenever that sprite is in a contact and otherwise left alone, so `BUMP` stays the event and this stays the detail of it. Making it clear itself when nothing touches would break the pairing, because `BUMP` accumulates across steps and a once-a-frame poll would find the detail already gone. Reading `BUMP` clears both, so they cannot disagree. Deliberately narrower than `akgl_Contact`: no actor pointers, because BASIC has no actor; no tile fields, because there is no tilemap; no z, because every test is planar; and **no `dt` and no `sensor`**, which libakgl documents as filled in by the resolver. This interpreter never resolves anything, so those two come back zero and mean nothing, and an always-zero field in a reference table is a lie. Documented with the two caveats that matter: fields 2, 3 and 4 are floats and want a `%` variable, and the contact *point* is exact only for two boxes -- libakgl's solver returns a point on the portal it converged to, while the normal and depth are exact for every pair. Chapter 8's collision section stops claiming only type 1 exists, which has been false since the previous commit. Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01EwxGB6TdoVvZ11KQQME9cL
62 lines
3.7 KiB
Markdown
62 lines
3.7 KiB
Markdown
# 12. Function reference
|
|
|
|
Every function, alphabetically, generated from the interpreter's own dispatch table.
|
|
|
|
A function is called with parentheses and yields a value; it cannot stand alone as a
|
|
statement. The arity column is how many arguments it takes — the interpreter checks it,
|
|
so a call with the wrong number is a syntax error rather than a surprise.
|
|
|
|
| Function | Args | Form | What it gives |
|
|
|---|---|---|---|
|
|
| `ABS` | 1 | `ABS(n)` | The absolute value of an integer or float. |
|
|
| `ATN` | 1 | `ATN(n)` | Arctangent, in radians. |
|
|
| `BUMP` | 1 | `BUMP(1)` | Which sprites have collided, as a bitmask. **Reading clears it.** |
|
|
| `CHR` | 1 | `CHR(n)` | The character for a Unicode code point, as a string. |
|
|
| `COS` | 1 | `COS(n)` | Cosine, in radians. |
|
|
| `ERR` | 1 | `ERR(n)` | The message text for an error code. `ERR(ER#)` names the last one. |
|
|
| `HEX` | 1 | `HEX(n)` | An integer as hexadecimal text. |
|
|
| `INSTR` | 2 | `INSTR(A$, B$)` | Where `B$` appears in `A$`, counting from zero, or -1. |
|
|
| `LEFT` | 2 | `LEFT(A$, n)` | The leftmost `n` characters. Clamped to the string's length. |
|
|
| `LEN` | 1 | `LEN(x)` | The length of a string, or the element count of an array. |
|
|
| `LOG` | 1 | `LOG(n)` | Natural logarithm. |
|
|
| `MID` | 3 | `MID(A$, start, len)` | A substring, counting from zero. |
|
|
| `MOD` | 2 | `MOD(a, b)` | The remainder of `a / b`. Integers only. |
|
|
| `PEEK` | 1 | `PEEK(addr)` | The byte at a real address. |
|
|
| `POINTER` | 1 | `POINTER(V)` | The address of a variable's value. |
|
|
| `POINTERVAR` | 1 | `POINTERVAR(V)` | The address of the variable structure itself, metadata included. |
|
|
| `RAD` | 1 | `RAD(n)` | Degrees converted to radians. |
|
|
| `RCOLLISION` | 2 | `RCOLLISION(n, f)` | What sprite `n` last collided with and how: what, which, the normal, the depth, the point, and which axis to reverse. See Chapter 8. |
|
|
| `RGR` | 1 | `RGR(f)` | The `GRAPHIC` mode (0), the drawing surface's width (1) or height (2) in pixels, or a character cell's width (3) or height (4). |
|
|
| `RIGHT` | 2 | `RIGHT(A$, n)` | The rightmost `n` characters. Clamped. |
|
|
| `RWINDOW` | 1 | `RWINDOW(f)` | The current text window's rows (0) or columns (1). Field 2 is a C128 screen mode and is refused. |
|
|
| `RSPCOLOR` | 1 | `RSPCOLOR(n)` | One of `SPRCOLOR`'s two shared registers, 1 or 2. |
|
|
| `RSPHIT` | 2 | `RSPHIT(n, f)` | One of `SPRHIT`'s settings for sprite `n`, in `SPRHIT`'s own argument order: 0 the kind, 1 to 4 the two corners. |
|
|
| `RSPPOS` | 2 | `RSPPOS(n, f)` | A sprite's x (0), y (1) or speed (2). |
|
|
| `RSPRITE` | 2 | `RSPRITE(n, f)` | One of a sprite's `SPRITE` settings, in `SPRITE`'s argument order. |
|
|
| `SGN` | 1 | `SGN(n)` | -1, 0 or 1 according to the sign. |
|
|
| `SHL` | 2 | `SHL(n, bits)` | Shift left. |
|
|
| `SHR` | 2 | `SHR(n, bits)` | Shift right. |
|
|
| `SIN` | 1 | `SIN(n)` | Sine, in radians. |
|
|
| `SPC` | 1 | `SPC(n)` | A string of `n` spaces. |
|
|
| `STR` | 1 | `STR(n)` | A number as a string. |
|
|
| `TAN` | 1 | `TAN(n)` | Tangent, in radians. |
|
|
| `VAL` | 1 | `VAL(A$)` | A string as a number. Refuses text that is not one. |
|
|
| `XOR` | 2 | `XOR(a, b)` | Bitwise exclusive or. |
|
|
|
|
## Reserved variables
|
|
|
|
Two things a C128 exposes as bare names are ordinary global variables here, because
|
|
this dialect has no variable name without a type suffix:
|
|
|
|
| Here | On a C128 | Holds |
|
|
|---|---|---|
|
|
| `ER#` | `ER` | the code of the last trapped error |
|
|
| `EL#` | `EL` | the line it happened on |
|
|
| `TI#` | `TI` | jiffies — sixtieths of a second — since the host's clock started |
|
|
| `TI$` | `TI$` | the same time as `HHMMSS` |
|
|
|
|
`ER#` carries this interpreter's error code, not a Commodore error number. There is no
|
|
correspondence to reproduce — the errors raised here are not the errors a 1985 ROM
|
|
raised — so print `ERR(ER#)` rather than the number. **[Chapter 15](15-error-codes.md)
|
|
lists every value it can hold.**
|