flan/examples/digits.fln

;;;; Drawing a number, now that the language can make one into a string.
;;;;
;;;; This file used to be the workaround for a gap: five of the ten ported
;;;; examples call raylib's `TextFormat` to put a number on the screen, and
;;;; nothing in Flan could reach `draw-text` with one — `i64->bytes` answered a
;;;; `[u8]`, `draw-text` wanted a `string`, and there was no bridge and no
;;;; allocator to build one in. So a number was drawn one glyph at a time out
;;;; of a `[10 string]` table.
;;;;
;;;; `string(b)` closed that. It is the mirror of `bytes-view(s)` and costs no
;;;; instructions — a `string` and a `[u8]` are the same 16-byte %slice — so
;;;; `string(i64->bytes(n))` draws in one call and the table, the per-glyph
;;;; pen and the digit arithmetic behind them are gone.
;;;;
;;;; What is left is the part `string(...)` does not answer, which is
;;;; *formatting*: `i64->bytes` has no field width, so "%03i" still has to be
;;;; assembled, and `f64->bytes` is `%g` and not "%.02f", so a fixed number of
;;;; decimal places still has to be split and drawn in two pieces. Those two
;;;; are why the file survives at all, and the three signatures are unchanged
;;;; so the five callers did not have to move.
;;;;
;;;; `TextFormat` itself is still not bindable, and not because of the FFI
;;;; rules: it is variadic, so its signature is not a signature, and it returns
;;;; a `char *` into a rotating static buffer, which `declare-c` refuses by
;;;; name anyway.
;;;;
;;;; `i64->bytes` and `f64->bytes` put their text in the temp allocator, where
;;;; it lasts until the next `free-temp()`. A program drawing these every frame
;;;; calls `free-temp()` once per frame, after drawing, and clones any text it
;;;; keeps longer.
;;;;
;;;; Everything here needs a window: `measure-text` answers 0 for every string
;;;; until init-window has loaded the default font, and a zero advance would
;;;; stack every piece on top of the first.

import rl "vendor:raylib"

;; Padding is drawn from a literal, one zero at a time. This is the last of the
;; old glyph table and it is here only because there is no field width.
const zero-glyph = "0"

;; One piece of text, and how far the pen moved. raylib's default font is not
;; monospaced — "1" is narrower than "8" — so the advance is measured rather
;; than assumed.
;;
;; Nothing may be formatted between the draw and the measure: `s` may be a view
;; of the shared buffer, and both calls have to see the same bytes.
fn draw-piece(s: str, x: i32, y: i32, size: i32, color: rl/Color) -> i32
  rl/draw-text(s, x, y, size, color)
  rl/measure-text(s, size)

;; How many decimal digits `n` has, for n >= 0. 0 has one. Only the padded
;; forms need it now — it is how many zeroes go in front.
fn digit-count(n: i32) -> i32
  let d = 1
      r = n / 10
  while r > 0
    d += 1
    r /= 10
  d

fn pow10(e: i32) -> i32
  let p = 1
  for i in range(e)
    p *= 10
  p

;; The whole number, in one draw-text. Answers the width drawn, so a caller can
;; put something after it — which is how the `TextFormat("%s: %i", ...)` shapes
;; in the C are reassembled here: draw the literal part with draw-text, then
;; this at x plus its width.
;;
;; The sign comes free now: i64->bytes renders "-7" itself, which also retires
;; the old note about i32's most negative value — it is widened to i64 before
;; formatting, so there is no negation to wrap.
fn draw-int(n: i32, x: i32, y: i32, size: i32, color: rl/Color) -> i32
  draw-piece(str(i64->bytes(i64(n))), x, y, size, color)

;; The same with a fixed minimum number of digits — the C's "%03i". A number
;; wider than `width` is drawn in full rather than truncated, which is what
;; printf does too.
;;
;; The zeroes are drawn first and the number after, so the one formatted value
;; is still live when it is drawn. A sign goes in front of the padding, as
;; printf's "%03i" does for -7 → "-07"; hence the magnitude is what gets
;; counted and the minus is drawn separately.
fn draw-int-padded(n: i32, width: i32, x: i32, y: i32, size: i32, color: rl/Color) -> i32
  let cx = x
      v = n
  if v < 0
    cx += draw-piece("-", cx, y, size, color)
    v = 0 - v
  let pad = width - digit-count(v)
  for i in range(pad)
    cx += draw-piece(zero-glyph, cx, y, size, color)
  cx += draw-int(v, cx, y, size, color)
  cx - x

;; "%.02f" and friends. `places` digits after the point, rounded by adding a
;; half at that scale before the split — so 0.999 at two places is "1.00" and
;; not "0.99", which is what the C's printf would have done and what a reader
;; comparing the two screens would expect.
;;
;; f32 and not f64 deliberately: every number this draws comes out of raylib,
;; and raylib's are floats. Widening them here would suggest a precision the
;; value does not have.
;;
;; `f64->bytes` is not used at all — it is "%g", which would print 0.5 for a
;; value asked for at three places and 1e+06 for a large one. The split into
;; two integers is what buys the fixed width, and it also keeps every formatted
;; value drawn before the next one is made.
fn draw-f32(v: f32, places: i32, x: i32, y: i32, size: i32, color: rl/Color) -> i32
  let cx = x
      av = v
  if av < 0.0
    cx += draw-piece("-", cx, y, size, color)
    av = 0.0 - av
  let scale = pow10(places)
      ;; The rounding and the split happen in one integer so the two halves
      ;; cannot disagree: rounding them separately is how "0.999" becomes
      ;; "0.100" — the fraction carries and the whole part does not hear
      ;; about it.
      total = i32(av * f32(scale) + 0.5)
      whole = total / scale
      frac = total % scale
  cx += draw-int(whole, cx, y, size, color)
  if places > 0
    cx += draw-piece(".", cx, y, size, color)
    cx += draw-int-padded(frac, places, cx, y, size, color)
  cx - x