;;;; raylib [text] example - text writing anim
;;;;
;;;; examples/text/text_writing_anim.c. Sixty lines of C whose whole substance
;;;; is one call this package cannot bind:
;;;;
;;;;     DrawText(TextSubtext(message, 0, framesCounter/10), ...)
;;;;
;;;; TextSubtext is in raylib.h and is not in the bindings, on the rule
;;;; raylib.flan states for the whole Text* family: it answers a `char *` into
;;;; a rotating static buffer, and declare-c refuses a returned pointer to
;;;; memory the caller does not own. There is no missing line to add — the
;;;; binding would be wrong at any signature.
;;;;
;;;; And it does not matter, because Flan has the operation as a primitive.
;;;; `(slice a lo hi)` takes a view of an array, `(string b)` reinterprets the
;;;; bytes as a string at no cost, and `(string (slice message 0 n))` is
;;;; TextSubtext with the static buffer removed — no copy, no shared state, no
;;;; rotation to run out of. Porting the example is therefore how the gap gets
;;;; *closed* rather than reported: the C's workaround for not having slices
;;;; is the thing Flan did not need.
;;;;
;;;; The one place they differ, and it is why the clamp below is here rather
;;;; than in the C: TextSubtext clips its length to the string, so the C can
;;;; pass a counter that runs past the end for ever and see nothing happen.
;;;; `slice` does not clip — an out-of-range bound is an error, and a bound
;;;; computed at run time is checked at run time — so the length has to be
;;;; brought inside the string before the call. That is a better failure than
;;;; the C's, and it costs one `min`.
;;;;
;;;; The message is a `[u8]` and not a `string` because `slice` takes an array
;;;; or a slice; `(bytes "…")` is the bridge in the other direction from
;;;; `(string …)` and costs nothing either. The embedded newline is written as
;;;; an escape, and raylib's draw-text breaks the line on it.

(import rl "vendor:raylib")

(defconst screen-width  800)
(defconst screen-height 450)

(defconst message
  "This sample illustrates a text writing\nanimation effect! Check it out! ;)")

(defvar frames-counter i32)

(defn main [] ()
  (rl/init-window screen-width screen-height
                  "raylib [text] example - text writing anim")
  (defer (rl/close-window))

  (set frames-counter 0)

  (rl/set-target-fps 60)

  (until (rl/window-should-close?)
    ;; Update. Holding space runs the counter eight times faster; enter starts
    ;; it over.
    (if (rl/key-down? :space)
      (set frames-counter (+ frames-counter 8))
      (set frames-counter (+ frames-counter 1)))

    (when (rl/key-pressed? :enter) (set frames-counter 0))

    ;; Draw
    (rl/with-drawing
      (rl/clear-background rl/raywhite)

      ;; One character every ten frames. The clamp is the whole difference from
      ;; the C — see the header comment.
      (let [b (bytes message)
            n (min (i32 (len b)) (/ frames-counter 10))]
        (rl/draw-text (string (slice b 0 n)) 210 160 20 rl/maroon))

      (rl/draw-text "PRESS [ENTER] to RESTART!" 240 260 20 rl/lightgray)
      (rl/draw-text "HOLD [SPACE] to SPEED UP!" 239 300 20 rl/lightgray))))